1. INTRODUCTION
1.1. River Guayas Basin
The Guayas River basin is the most important fluvial system in the country of
Ecuador and in the South American Pacific coast. It occupies a land surface
that extends between 0° 15’ and 2° 25’South latitude and 78° 40’ and 80° 20’
West longitude, on the coast of the country, on the west side of the Andes
mountains. Its extension covers about 35,000 km2 and comprehends, either
completely or partially, 11 of the 24 provinces of Ecuador (Figure A.1 in
Appendices), among them Guayas, Manabi, Los Ríos, Santa Elena, Santo
Domingo de los Tsáchilas, Chimborazo, Cañar, Bolivar and Cotopaxi, which
correspond approximately to 13% of the country territory and includes
4,800,000
inhabitants,
roughly
40%
of
Ecuador’s
total
population.
Approximately half of this 40% live in Guayaquil, Ecuador biggest city, and its
surroundings. Guayaquil is located on the west bank of the Guayas River, in the
vicinity of its point of origin, which is formed by the confluence of the Daule and
the Babahoyo Rivers (Figure A.2 in Appendices). As its main port, the city is the
center of Ecuador economic and industrial activities. It represents both a
gateway for import products and an exit door for the country exportations. The
presence of the Guayaquil within the River Guayas watershed adds more
importance to it, due to the economic activities that take place on its area of
influence. These activities include:
 Agriculture
 Industry
 Mining
 Commerce
1.1.1. Agriculture
The Guayas River catchment is a very important region for the Ecuadorian
economy by making a high contribution to Ecuador’s gross domestic income
1
(GDI), putting up around 40% of its current value. It is estimated that
approximately 300.000 hectares within the basin are of easy irrigation for
farming purposes. The main agricultural activities taking place on this region
are:

Export products:
o Coffee
o Cocoa plant
o Sea products
o Bananas

Internal consumption products
o Rice
o Soy
o Sugarcane
o Corn
o Oil Palm
o Fruits and vegetables

Industrial raw material
According to Ecuador’s Central Bank, the total amount of the country’s
agricultural exportations raises up to USD 1,672,590,000, 54% of which is
generated on the Guayas River basin.
1.1.2. Industry
The city of Guayaquil, capital of the Guayas province, is the main harbor of
Ecuador and also the most important commercial and industrial centre of the
Guayas River basin, followed by the cities of Babahoyo, Milagro and
Quevedo. It has been estimated that along the Guayas River watershed,
approximately 500 different manufacturing industries are located, some of
which are:

Food

Beverages
2

Dairy products

Textile

Pharmaceutical

Plastic
1.1.3. Mining
The mining industry on the Guayas River Basin area comprehends basically
the exploitation of two main mineral groups:

Metallic minerals, such as silver, zinc, lead, etc.

Non-metallic minerals that are primarily used as construction materials.
1.2. Guayas River Basin Management Issues.
In the year of 1965, the “Comisión de Estudios para el Desarrollo de la Cuenca
del Rio Guayas” (CEDEGE) was created. Its main purpose was to organize the
elaboration of the necessary studies that were required to achieve the design of
a development program for the river basin. The institution evolved through three
different stages (Herrera 2005):
 First stage: emphasized in the execution of the required studies needed to
make possible the development of the basin.
 Second Stage: due to the elaboration of a National Plan of Transformation
and Development, designed by the Central Government during the 70s
decade, CEDEGE published a Regional Plan for the Development of the
Guayas River Basin which included the definition of limits and guidelines for
the exploitation of natural resources, agricultural activities and land use
policies.
 Third Stage: the main hydraulic projects were finished and CEDEGE
encouraged its massive exploitation.
3
Unfortunately, Ecuador lacks appropriate policies regarding its water resources.
CEDEGE has undertaken important water related projects in the basin, such
as:
 The Daule Peripa Dam
 Various irrigation projects
 Flood control projects
However, there has been little interest in developing a integrated catchment
management plan and as consequence, CEDEGE’s operation has struggled
over the years with financial difficulties which have prevented it from effectively
managing the water resources within the Guayas basin and has threatened to
severely affect and deteriorate the hydraulic system of the region, situation
which, due to the Guayas River system importance would have a serious
impact on the fragile economy of several provinces of Ecuador. Until the year
1995, CEDEGE was in charge of operating the different river gauging stations
that are located within the Guayas River catchment, from that year on, the
Instituto Nacional de Meteorologia e Hidrologia (INAHMI) took over those
responsibilities. However it has also suffered from lack of funding that has
limited its ability to contribute for an efficient catchment management, therefore
available information about sediments, precipitation and discharge within the
Guayas River system is rather scarce and given that the sampling procedures
have not been standardized by the corresponding institution, the existing data is
not reliable. Also, water quality issues receive very limited attention, hence very
little is known about the river chemical and ecological status. INTERAGUA,
which is Guayaquil potable water company, carries out a water quality
monitoring program in the Guayas River estuary and at the local water
treatment plant, located on the margins of the Daule River. However these
actions are only focused on water supply requirements and are not part of any
bigger scale water quality monitoring plan.
4
The effects of storm water and sewage discharges on the river have also been
many times overseen when dealing with the river managing issues, especially
in the case of the drainage systems from Guayaquil, which has a great
percentage its drainage networks discharging into the Daule River. The city
possesses separate systems for storm water and sewage, the former being
directly discharged into the stream without treatment of any kind and the latter
being discharged into the river after a very basic treatment system, composed
by settlement tanks and small oxidation ponds. Some of this system even
discharges directly to the river without previous treatment. Therefore, the water
fed into the river carries a very high suspended sediment load that adds to the
effect of the natural load of suspended sediments that is being transported by
the stream.
1.3. The Guayas River
The Guayas River is formed by confluence of two tributaries, the Daule River
and the Babahoyo River . The former has a basin extension of approximately
13,280 km2 and is originated on the elevations of the province of Manabi; it
contributes with an estimate of 40% of the discharge to the Guayas River. The
latter has a drainage basin of around 18,220 km2 and is originated in the Andes
Mountains; it contributes with about 60% (up to 66% during the rainy season of
the year) of the discharge. After the confluence of these two streams the
Guayas River has an extension of 55 km with a very mild slope, in the order of
0.2%, until its discharge point into the Pacific Ocean. Along its path the Guayas
River forms several islands, before discharging to the ocean through a delta
system configuration; its width fluctuates between 1.5 and 3 km and its depth
vary between 5 and 12 meters; the deepest stretches of the river are found in
front of the city of Guayaquil. The main characteristic of the Guayas River
resides in the fact that it constitutes a tidally dominated estuarine system. The
tidal effect can be observed over distances of around 120 km upstream of
Guayaquil for the case of the Daule River and approximately 93 km upstream of
Guayaquil in the Babahoyo River (USACE, 2005). The discharge that is carried
5
by the tides, twice a day, into the rivers Daule and Babahoyo has been
estimated, according to previous research performed on the subject, between
7000 and 13000m3/s, values that are many times greater than those estimated
for the peak discharges coming from both rivers Daule and Babahoyo, therefore
the Guayas’ characteristics are governed by tidal flow rather than by the
freshwater flow (USACE 2006). However, the primary direction of sediment
transport has been determined to be downstream the two rivers.
1.3.1. Discharge and Currents Data
1.3.1.1
Discharge
CEDEGE keeps the records of discharge values taken at different gauging
stations within the Guayas River Basin. For the elaboration of this study
CEDEGE has provided of discharge values taken at La Capilla gauging
station on the Daule River (Table 1), and also from the discharges recorded
at Zapotal and San Pablo stations (Tables 2 and 3), on two Babahoyo River
tributaries, the Catarama River and the San Pablo River respectively. The
confluence of these two streams forms the Babahoyo River, therefore
adding together the recorded streamflow data from the Zapotal and San
Pablo stations is supposed to give an approximate value of the flowrate
corresponding to the Babahoyo River. However, it needs to be noted that in
the case of the gauging station of the Daule River, it is located several
kilometers downstream of the Daule Peripa Dam, at a point after which the
river does not receive any important water input coming from big tributaries,
thus generating representative spatial data of the river, even though there’s
no information on the discharges upstream of the dam to compare with. In
the other hand, this is not the case of the other two gauging stations, located
on the Babahoyo River basin. These stations, located on the headwaters of
the Babahoyo River, doesn’t provide a reliable estimate of its flowrate
because downstream of the gauging stations the Babahoyo River receives
the input of two very important affluents, the Vinces and the Chimbo Rivers,
which incorporate a large amount of water into the Babahoyo River.
6
Therefore, the addition of the recorded values of discharge on these two
gauging stations is expected to be much less than the actual discharge of
the river at its low basin, before it converges with the Daule River.
3
Mean monthly discharge (m /s) - Daule Gauging Station at La Capilla
Month
January
Year
1963
37.46
1964
285.33
1965
70.20
1966
576.01
1967
558.56
1968
44.35
1969
53.00
1970
63.40
59.52
1971
103.93
1972
987.51
1973
37.60
1974
410.96
1975
519.42
1976
194.96
1977
72.95
1978
47.43
1979
25.72
1980
16.65
1981
67.27
1982
1528.22
1983
76.84
1984
226.18
1985
700.79
1986
467.64
1987
152.42
1988
109.78
1989
92.36
1990
37.12
1991
79.81
1992
122.70
1993
144.39
1994
248.40
1995
84.99
1996
1997
1439.11
1998
97.40
1999
276.14
2000
581.12
2001
96.67
2002
390.18
2003
227.32
2004
205.65
2005
195.05
2006
302.60
2007
February
March
April
May
June
July
August
September
155.78
517.95
408.02
1108.39
880.90
189.84
56.67
221.03
532.05
614.48
999.37
408.46
1153.43
933.54
486.82
459.98
220.72
179.42
640.74
294.77
1276.50
898.29
305.16
512.67
1317.95
649.93
679.14
109.76
144.21
314.32
550.72
384.72
684.03
209.58
671.42
1113.66
1289.71
395.27
658.37
266.33
435.03
250.39
1373.95
1096.07
957.50
460.77
1341.08
113.00
990.48
470.32
331.06
144.18
907.33
132.33
1401.66
1206.08
532.61
402.35
1455.36
418.90
634.79
91.00
143.06
1781.03
1079.43
391.02
244.84
547.89
238.86
1321.55
1435.86
398.84
176.27
245.56
870.53
1307.19
609.24
836.46
1304.97
117.69
1088.51
1387.04
471.07
638.97
434.24
697.13
536.05
151.07
1536.87
770.62
183.29
742.16
1094.34
142.19
738.67
110.91
85.94
1521.37
1279.16
646.64
268.25
244.78
153.68
193.90
1040.44
228.88
145.30
51.58
661.37
677.67
126.67
245.91
734.52
193.60
269.28
802.67
162.07
318.74
96.25
294.37
93.10
109.47
1119.01
362.18
112.91
368.13
805.67
392.50
47.26
89.69
339.81
115.91
82.07
25.25
417.04
166.51
63.28
678.94
199.01
56.78
154.91
267.70
108.55
87.20
75.33
86.17
43.92
42.63
917.69
122.76
76.54
96.23
171.24
84.63
67.41
52.48
1281.85
644.67
621.32
146.48
128.75
53.97
37.63
444.81
21.01
60.55
142.63
50.19
39.85
15.60
108.77
79.77
31.13
348.38
108.11
31.12
86.61
119.14
56.94
44.85
44.38
40.79
30.66
24.70
783.77
81.02
51.50
61.33
85.89
59.84
420.08
48.92
37.45
213.45
148.75
13.14
42.20
69.57
45.80
25.92
10.79
34.50
46.20
21.12
93.81
62.25
21.09
53.93
65.74
32.21
25.67
26.97
26.06
20.92
15.20
413.15
56.70
36.58
44.67
72.55
51.72
104.14
46.62
34.72
100.11
128.88
80.79
9.61
30.06
44.36
21.40
17.06
8.17
20.75
29.45
14.81
52.78
44.04
14.82
37.75
38.51
21.55
18.33
26.21
16.68
18.25
12.31
356.43
46.75
26.03
33.70
41.19
47.22
56.90
43.71
31.03
75.96
121.73
68.23
68.82
88.20
152.63
144.41
1339.73
538.57
312.16
588.00
413.93
636.89
333.48
189.39
666.82
262.99
1769.99
855.05
393.72
675.27
853.52
510.71
334.43
259.83
635.98
542.25
1910.76
1126.94
1454.06
771.03
393.94
492.29
547.96
210.52
184.81
221.44
162.33
290.22
1123.26
347.92
200.56
194.90
216.82
172.89
170.62
163.50
145.06
227.41
480.35
252.95
178.37
119.40
242.41
159.30
151.84
152.70
224.45
354.87
160.94
170.67
100.93
204.04
152.39
145.15
145.87
224.64
267.17
130.18
161.53
100.04
182.32
145.29
141.02
145.79
219.13
1268.47
860.90
265.45
308.34
546.70
243.87
610.76
258.66
111.46
96.89
October November December
8.07
27.28
28.56
22.18
19.40
6.54
13.97
23.32
13.82
44.78
33.82
13.76
28.68
26.22
18.01
13.13
19.09
14.62
12.62
57.10
145.27
37.94
21.56
31.42
35.88
40.70
51.09
47.68
50.64
124.85
59.34
222.49
0.00
173.69
135.28
189.13
145.79
141.37
143.35
239.59
6.20
21.67
28.89
12.20
11.92
6.22
12.54
18.75
10.97
25.26
25.84
10.99
21.56
22.56
12.65
11.13
12.82
12.68
12.94
467.47
88.36
29.69
17.64
37.59
24.07
51.38
51.57
46.49
28.40
79.71
215.18
50.63
43.20
82.40
9.02
18.86
25.02
13.27
9.31
4.94
13.64
20.46
24.01
647.83
23.76
24.83
24.97
28.34
15.09
10.74
12.05
13.50
13.37
902.91
87.71
59.42
39.68
31.54
24.97
57.58
75.54
52.90
36.69
75.14
160.89
82.28
42.21
54.70
176.17
213.92
134.97
241.04
344.21
93.66
306.86
216.42
210.20
227.74
274.06
158.98
261.09
214.96
187.70
182.81
708.73
Table 1. Mean monthly discharge data, recorded at La Capilla gauging station on the
Daule River. (CEDEGE)
7
3
Mean monthly discharge (m /s) - Zapotal Gauging Station at Catarama
Month
Year
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
January February
122.87
378.95
74.88
351.07
245.14
129.72
137.98
70.54
38.51
27.15
112.56
709.73
126.86
141.1
369.73
229.17
136.4
218.99
53.16
47.52
227.77
117.22
168.36
294.7
70.52
95.84
453.67
601.27
341.01
616.33
611
314.21
332.62
282.27
304.79
359.3
317.78
597.41
457.93
205.41
434.61
44.78
238.91
95.02
38.16
44.04
105.88
342.13
372.8
190.92
142.75
601.5
280
384.12
604.38
315.6
428.61
522.86
641.83
503.1
369.13
368.23
364.36
March
April
May
603.07
509.76
449.46
659.55
623.49
484.77
376.21
498.88
202.55
436.13
239.05
493.27
587.76
413.18
293.44
493.21
298.87
615.86
210.38
389.43
604.92
612.08
416
261.45
512.83
562.38
471.2
625.25
221
480.14
609.66
391.01
423.84
337.14
476.75
305.99
262.65
572.74
356.15
164.24
439.33
463.63
219.91
447.52
244.86
261.27
556.59
509.83
461.3
361.78
313.47
488.75
233.47
329.87
215.55
214.71
326.5
171.21
243.26
149.01
225.13
120.31
153.5
516.33
641.97
380.84
316.56
203.92
515.43
461.12
578.37
360.32
484.63
360.15
395.13
242.89
339.76
211.8
245.54
136.99
174.99
128.51
201.06
366.81
218.41
250.58
142.05
153.97
443.49
223.51
223.55
135.06
119.9
357.96
June
282.73
146.62
83.08
131.11
151.45
82.83
92.49
79.6
104.33
55.32
73.25
410.78
87.16
77.35
78.87
117.15
82.75
93.88
70.03
74.55
220.37
109.09
94.35
75.87
59.16
86.32
108.42
94.64
117.25
49.57
59.34
July
August
September October November December
25.08
47.39
38.06
26.68
33.73
33.9
26.72
23.91
24.13
21.51
21.13
21.67
141.56
34.33
25.61
25.48
23.87
40.42
31.92
25.63
29.61
25.05
22.24
19.24
18.92
18.41
16.78
32.24
89.04
31.17
19.89
23.29
21.27
35.8
25.97
22.84
25.57
21.56
17.23
17.23
13.98
16.01
16.08
266.43
72.14
26.16
17.51
22.96
35.27
146.05
28.88
57.16
24.26
34.84
22.87
20.36
13.71
16
19.72
565.53
138.76
40.4
36.67
28.63
27.41
27.42
20.66
20.27
29.18
28.11
26.41
25.9
20.72
21.97
28.05
17.69
15.81
22.87
22.55
21.14
21.68
17.9
22.45
21.39
14.73
13.13
18.57
19.94
19.17
21.9
14.74
26.27
22.54
20.63
38.21
19.57
32.49
28.48
28.9
14.31
12.99
143.35
81.26
50.69
74.57
93.82
50.22
52.12
44.65
50.73
37.19
43.05
293.98
56.99
48.81
49.07
56.8
50.93
57.39
41.13
44.43
69.28
58.61
53.9
51.82
39.43
68.29
49.41
34.12
45.54
50.34
33.04
33.66
30.09
33.1
25.92
29.33
160.68
40.62
34.78
33.57
44.23
34.42
36.95
28.85
28.82
41.71
36.49
35.89
36.12
26.87
61.27
59.58
54.83
41.98
38.82
28.22
38.52
27.61
22.08
21.41
16.53
25.97
49.84
32.68
22.05
16.66
29.08
Table 2. Mean monthly discharge data, recorded at Zapotal gauging station on the
Catarama River. (CEDEGE)
8
3
Mean monthly discharge (m /s) - San Pablo Gauging Station at El Palmar
Month
Year
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
January February
March
April
May
June
July
August
54.49
31.72
68.45
159.84
34.01
71.67
74.73
68.39
25.06
27.03
10.69
8.45
34.68
78.52
114.32
150.87
201.56
119.39
197.26
207.54
186.70
139.69
68.87
142.88
137.75
96.49
74.33
177.62
219.99
181.08
139.59
210.83
210.85
245.38
136.45
167.54
75.29
217.43
74.49
103.41
152.21
174.51
167.87
42.35
173.48
199.68
134.71
146.45
100.32
196.20
135.50
69.20
97.50
45.71
85.54
97.52
56.36
71.54
120.49
95.22
60.61
37.97
78.01
31.14
22.24
139.37
29.86
246.06
186.33
126.74
89.36
12.49
13.60
54.94
45.67
179.55
66.86
132.51
44.05
243.77
233.46
241.31
316.40
132.14
190.72
224.80
261.71
203.00
231.54
119.28
171.32
141.47
219.62
133.36
294.56
116.31
218.96
288.93
284.66
290.61
82.62
91.54
59.82
192.86
266.32
99.86
162.73
112.75
53.88
153.16
25.47
42.59
69.47
25.22
2.17
29.53
32.47
298.80
149.69
163.99
139.49
88.46
10.85
267.08
124.36
230.68
269.47
293.40
169.58
108.76
73.15
254.07
19.30
September October November December
8.02
10.99
9.85
24.77
15.93
11.47
15.59
18.51
10.48
8.27
7.25
8.21
6.52
4.91
50.65
7.86
3.99
5.59
12.17
5.27
4.75
4.06
4.17
9.31
6.70
32.61
3.61
7.03
6.72
6.72
12.71
11.36
195.36
216.32
251.95
6.72
17.13
14.20
52.41
24.63
14.25
25.03
31.84
15.10
14.65
7.75
13.43
10.79
7.75
91.62
13.37
7.16
10.34
16.70
9.85
16.46
7.96
6.20
22.53
15.34
36.36
5.48
10.67
8.12
8.00
15.32
13.86
44.51
24.43
49.30
147.94
145.61
93.08
52.09
29.29
143.65
86.55
89.62
123.89
6.86
35.86
20.86
84.48
40.40
21.57
42.24
62.00
25.25
23.08
11.30
27.83
14.54
9.90
128.61
28.40
13.46
16.37
41.95
61.11
24.76
15.25
14.47
63.98
40.49
55.75
8.98
12.18
13.78
8.08
5.88
4.87
5.21
4.96
3.97
32.46
6.99
2.29
3.43
5.90
2.37
3.58
2.30
2.10
6.35
3.52
3.49
2.99
10.18
9.85
7.09
3.78
4.34
4.13
2.84
5.31
32.24
5.63
1.71
3.32
5.55
1.63
3.68
1.68
1.05
4.83
2.44
3.12
2.31
140.24
255.08
250.13
119.51
205.44
100.76
123.06
109.03
23.54
22.56
24.50
17.05
25.82
4.84
7.52
37.64
10.64
5.24
3.09
8.18
79.96
103.20
49.76
67.91
32.44
23.90
45.60
8.75
9.06
7.99
1.66
2.62
8.11
4.85
3.67
2.54
0.48
1.25
2.27
1.70
1.44
0.11
0.14
2.73
1.17
0.65
0.07
0.11
5.72
5.46
5.61
9.81
7.63
6.47
8.41
17.16
5.81
3.10
2.72
3.78
2.84
35.76
37.10
3.90
1.82
2.61
4.99
3.25
2.58
1.04
0.80
3.97
1.82
2.59
8.24
5.58
7.29
74.52
6.85
14.23
12.06
13.87
5.41
5.65
3.09
4.23
4.94
114.90
129.34
8.71
11.60
16.74
7.54
10.56
4.85
3.14
34.79
4.46
20.04
60.00
18.60
2.38
0.32
0.72
0.02
0.18
4.09
3.77
0.43
5.27
2.20
Table 3. Mean monthly discharge data, recorded at San Pablo gauging station on the San
Pablo River. (CEDEGE)
1.3.1.2.
Currents
Ecuador Instituto Nacional Oceanográfico de la Armada (INOCAR)
performed in 2001 a local study of the currents on the Daule and Babahoyo
Rivers near their confluence, at the point of the Unidad Nacional Bridge
crossing. It established two different flow directions, corresponding to the
9
tide flux and reflux, and two levels, surface and medium. Residual currents
values were determined by subtraction of the tidal currents (flux and reflux).
The currents were measure in 12 stations, six of them in the Daule River
and the other six in the Babahoyo River. In some stations, for the case of
the reflux condition, in some stations the velocity readings could not be
taken due to the shallow water level. From that study the results shown in
Tables 4, 5 and 6 were obtained.
Daule River
Tide condition
Station
1
2
3
4
5
6
Station
1
2
3
4
5
6
Flux
Mean
Velocity
(m/s)
0.36
0.62
0.43
0.69
0.79
0.61
Max.
Velocity
(m/s)
1.5
1.03
1.41
1.63
1.56
1.34
Mean
Velocity
(m/s)
0.6
0.65
0.28
0.55
0.6
0.64
Max.
Velocity
(m/s)
1.31
1.01
1.3
1.4
0.8
1.1
Level
Surface
Surface
Surface
Surface
Surface
Surface
Level
Medium
Medium
Medium
Medium
Medium
Medium
Table 4. Mean and maximum velocities in the Daule River (INOCAR)
10
Tide condition
Station
1
2
3
4
5
6
Reflux
Mean
Velocity
(m/s)
0.38
0.69
0.57
0.78
0.88
0.74
Max. Velocity
(m/s)
1.68
1.24
1.55
1.81
1.67
1.71
Level
Surface
Surface
Surface
Surface
Surface
Surface
Table 4 (cont). Mean and maximum velocities in the Daule River (INOCAR)
Babahoyo River
Tide condition
Station
7
8
9
10
11
12
Station
7
8
9
10
11
12
Flux
Mean
Velocity
(m/s)
0.83
0.69
0.33
0.31
0.44
0.78
Max.
Velocity
(m/s)
1.62
1.6
1.58
1.9
1.3
1.44
Mean
Velocity
(m/s)
0.72
0.62
0.27
0.26
0.3
0.67
Max.
Velocity
(m/s)
1.41
1.01
1.3
1.4
0.85
1.14
Level
Surface
Surface
Surface
Surface
Surface
Surface
Level
Medium
Medium
Medium
Medium
Medium
Medium
Table 5. Mean and maximum velocities in the Babahoyo River (INOCAR)
11
Tide condition
Reflux
Station
Mean
Velocity
(m/s)
Max. Velocity
(m/s)
Level
1
2
3
4
5
6
0.97
0.84
0.44
0.37
0.65
0.88
1.86
1.95
1.95
2.16
1.76
1.59
Surface
Surface
Surface
Surface
Surface
Surface
Mean
Velocity
(m/s)
0.71
0.77
Max. Velocity
(m/s)
1.16
1.31
Level
Station
1
2
Medium
Medium
Table 5 (cont). Mean and maximum velocities in the Babahoyo River (INOCAR)
Station
Mean Velocity
(m/s)
1
2
3
4
5
6
7
8
9
10
11
12
0.02
0.26
0.14
0.3
0.34
0.29
0.14
0.15
0.31
0.27
0.21
0.1
Table 6. Mean velocities of residual currents (INOCAR)
12
The direction of the superficial and sub-superficial currents show, in the
Babahoyo River, a tendency to flow in a northeastern direction during the
flux conditions and in a southwestern direction during the reflux condition. In
the Daule River, INOCAR points out that the tendency of the currents during
the flux condition is to follow northeastern and northwestern directions and
in the reflux conditions the currents follows a southern direction. The
location of the stations on the rivers and detail of the currents directions is
shown in the Figures A.4, A.5, A.6 and A.7 in the Appendices section.
1.4. Sediment Transport Conditions
As mentioned in section 1.3 the main direction of sediment transport
corresponds to the downstream flow. It has been observed in previous studies
that the predominant form of sediment transport in both Rivers Daule and
Babahoyo and also in the Guayas River consists in suspended soil particles. The
sediment transport processes within the Guayas River system are heavily
influenced by the estuarine environment of the river system, which directly
influences the deposition of those suspended sediments. According to the
monitoring records of CEDEGE from the period consisting between the years
1970 to 1980 the Guayas River receives a suspended sediment load form the
Daule River of about 8.3 million tons per year. This period corresponds to the
fluvial conditions prior to the construction of the Daule – Peripa dam. CEDEGE
also predicted that, after the dam, the Daule River would carry and approximate
of 6.1 million tons per year into the Guayas River, however due to the lack of
sediment monitoring after the year 1980, this prediction has not been verified
with real measured data. It is important to mention that INOCAR has measured
the suspended solid concentration to be between 50 and 500 ppm, during a
period, which for a sedimentation study is very short, comprehended between
the months of October 2002 and September 2003.
13
1.5. Consequences of sedimentation in the Guayas River system
The main concern regarding the sedimentation processes in the Guayas River is
the increased flooding hazards that are linked to the reduction of the river
section, especially in the vicinity of the city of Guayaquil. Floods are normally
present in the low regions of the both Babahoyo and Daule river basins even
during the regular periods of rain of the year, but the risks of severe flooding
events are greatly increased due to the climate change and the recurrent
presence of El Niño phenomenon, and can affect both rural and urban areas.
Special notation needs to be made for the consequences of flooding in
Guayaquil, which has a large part of its storm water drainage system discharging
on the Daule River, especially from the north zones of the city, which consists
mostly in middle and upper class urban development projects, with house
constructions ranging between US$ 60,000 and US$ 1,000,000. El Palmar
Island constitutes a fluvial geomorphic feature of the Guayas River system that,
due to its location, is considered to be directly related to the flooding of adjacent
zones, such as the aforementioned city of Guayaquil, given that at this point of
its development the island represents an obstruction to the flow coming from the
Daule River, provoking an increment on the water surface levels upstream of its
location (backwater effect). Also, it has been observed that its presence seems
to be causing an adjustment of the stream, in order to accommodate the island,
by scouring the right bank and putting in danger several nearby structures. This
scouring process can be observed by analyzing and comparing the bathymetric
information provided by INOCAR from several past years. This erosive process
has also been mentioned in the sedimentation study performed by the United
States Army Corp of Engineers (USACE) on the Guayas River in the year 2005,
on which a river cross section was plotted using the aforementioned bathymetric
data. The resulting graph is shown in Figure A.8 in the Appendices section. As it
can be observed there’s a marked tendency of the river to increase its depth on
its right bank.
14
1.6. El Palmar Island
The formation of islands seems to be a natural and recurrent process within the
Guayas River system; some of these islands have become established features,
for example the Isle of Santay, in front of the city of Guayaquil, some others only
appear temporarily and are washed away during flooding events. El Palmar
Island, at the confluence of Daule and Babahoyo rivers, in the proximity of the
city of Guayaquil and at a latitude of approximately 2° 9'56.00"S and a longitude
of 79°52'15.53"W (Figure A.9 in Appendices), is one of the islands that has
formed in the lowest regions of the Daule river and in the delta created by the
Guayas river before it discharges into the ocean. This isle is a dynamic fluvial
geomorphic structure formed by the deposition of river sediments, which has
been developing over the course of at least 50 years, at the mouth of the Daule
River. The island was first originated from a mid channel bar, the first graphical
evidence of which can be seen on a 1966 aerial photograph (USACE, 2005).
Currently, El Palmar Island possesses a sub-triangular geometric configuration.
It occupies the Daule River channel and has not extended into the Babahoyo
River, its southeast margin outlines the continuation of said river’s channel;
however given its location the island receives sediments from both rivers. The
island divides the Daule River into two channels, establishing as the main
channel, which possesses the strongest current, the one located between the
south end of the island and the Santa Ana Hill (Figures A.10a and A.10b in
Appendices). On the other side, the channel located on the east side of the
island shows evidence of severe sedimentation, as it can be easily observed
during the periods of low tide (Figure A.11 in Appendices). Due to the presence
of the island that main Daule channel has shown a tendency to scour its right
over bank and the riverbed, effect that has been determined by comparing the
bathymetric data, provided by the INOCAR, from various years, which shows a
marked increment of depth over time.
There are two different zones that are easily identified on the island. The first
one corresponds to the stabilized part of the isle. It possesses a very dense
15
herbaceous vegetation cover and occupies roughly the southern half of the
island. On this part of the island the soil appears to be stabilized due to the
presence of the vegetation. The other zone corresponds to the northern half,
which presents very little vegetation or newly established plants. This part of El
Palmar Island is of very difficult access due to the combination between the
loose nature of the soil and its high moisture content. The northern zone of the
island is completely covered by the water and can is not seen during the high
tide periods.
1.6.1. Temporal Growth of Island
The bathymetric surveys undertaken by INOCAR have proven to be useful for
determining the overall progressive evolution of the island shape since its
appearance, which has been variable through time but with a marked
tendency to increase its overall size (Figure 1), both as an expansion in width
and as an increase of its length (N-S axis). From the general shape of the
island on its current state allows suggests that it has developed from a point
bar at the mouth of the Daule River on its confluence with the Babahoyo River.
The north end of the island doesn’t show much variation since 1985, only
increasing its width, but the southern end of the island has sustainably
increased its extension on the same direction, helping to achieve the current,
near triangular, shape of the island. Also from a cross section plotted by the
USACE (Appendix A. Figure A.8) it can observed that, while there’s a
increment in the depth of the channel bottom on the right bank of the river,
there’s a general trend to reduce the cross sectional area, due to aggradation
processes that
have taken place within the river over time. The same
research pointed out that, through the analysis of the INOCAR bathymetric
data over the years 1975, 1991, 1999 and 2003, it was determined that the
growth rate of the island was accelerated by the presence of the El Niño
events from the years 1982 – 83 and 1997 – 98. The accelerated deposition of
material on the island can be observed in Figure 2, where the variations of the
geomorphology of the island over time are shown. In the cross section
16
corresponding to the year 2001 there is a marked increment of the island
surface elevation, perhaps originated in the deposition of the great amount of
suspended sediment that was brought in to the river system during the1997 –
98 El Niño event. However, this loose soil particles were partially removed by
the currents in the following years, as it can be seen in the cross section from
year 2003. In the plot corresponding to the year 2008 it is evident that the
island has varied his profile markedly but the overall tendency of the river is to
continue with a sedimentation pattern on the zone of the island and scouring
the right bank of the Daule River.
Figure 1. Temporal development of El Palmar Island since the year 1982
(USACE, 2005)
17
Figure 2: Morphologic variations of El Palmar Island over different years. (INOCAR)
1.6.2. Factors affecting island growth
Even though it is a general agreement that the island formation is a natural
process corresponding to any river system dynamics, previous studies have
identified several factors to be a direct influence in the rate of growth and
development of the island during the course of years. Some of these factors
have been recognized to be more relevant than others, as the main issue that
concerns the Rivers Daule, Babahoyo and Guayas is the acceleration of the
deposition rate of sediments on El Palmar Island, among the main possible
causes of the increased sedimentation of the island the following factors have
been pointed out:

Land use

El Niño Events

Deforestation

Tide regime

Daule – Peripa Dam
18
It is also important to mention that, even though it is not commonly included
among the factors that affect the development of the island, the Unidad
Nacional Bridge, located approximately 1 kilometer upstream of the island,
might be affecting the growth of the island due to the riverbed scouring
processes that take place at its crossing.
1.6.2.1.
Land Use
Human activities are responsible for the speeding up of erosive processes
within river catchments. These activities radically upset the delicate balance
that
nature has
developed between
rainfall and runoff.
Farming,
construction, logging, and mining are the major causes of accelerated
erosion, which can be minimized through careful land use planning and by
implementing appropriate control measures. The land use factor is highly
correlated to the deforestation of the land within a river basin. Within the
Guayas River basin agricultural activities have greatly increased over the
last two decades and therefore they are considered to be a extremely
important factor affecting the sediment production.
1.6.2.2.
El Niño Events
The El Niño phenomenon, which presents itself on the Pacific Ocean, is
related to an elevation of the ocean surface and with the thermal anomalies
affecting it. This event usually entails strong droughts or flooding
occurrences. Under normal conditions the atmospheric currents cause the
slight movement of a volume of water of the Pacific Ocean towards its East
coast. When influenced by El Niño conditions, and because of some still
unknown reasons, the atmospheric currents are altered, thus diminishing
their intensity in their usual direction (West - East) or even reversing it. This
diminution or even reversal causes a variation of the ocean level, which in
some El Niño events can reach up to 40 cm. At the same time, an increase
of the surface temperature of the ocean (up to 8° C, as recorded in the 1982
El Niño event) and a reduction of the thermocline (The thermocline is the
19
transition layer between the mixed layer at the surface and the deep water
layer. The definitions of these layers are based on temperature) occurs. At
the coast, natural currents originated by the impact of the aquatic mass on
the continent are responsible for mixing warm and cold waters. During an El
Niño period, the reduction of the thermocline prevents this mixing of the
waters, since the current doesn’t descend with the thermocline. The thermal
anomaly of the oceanic surface alters the usual climate of the affected
regions (which includes the coast of South America, especially Colombia,
Ecuador and Peru, and archipelagoes of the Pacific like the Galápagos
Islands). This alteration pronounces itself in form of strong floods and
droughts. During the periods of strong pluvial precipitation, a greater
percentage of the rainfall will become runoff.
The extreme climatic and hydrologic conditions that are brought in by the El
Niño phenomenon provokes unusually high discharges values by both
Daule and Babahoyo Rivers, which in turn are accompanied by very high
sediment loads being transported by the streams. It has been observed in
previous research on the Guayas River sedimentation that after two
extremely severe el Niño events (years 1982 – 83 and 1997 – 98) the
growth rate of the island increased significantly.
1.6.2.3.
Deforestation
Frequently, the result of the deforestation is the erosion of the soil. In the
absence of vegetation cover, trees in special, rain strikes the soil directly,
instead of dripping gradually from the branches and leaves and falling
smoothly on the ground. This means that when it rains, more water will hit
the soil strongly, therefore dragging it. Most forests’ soils are covered by a
superficial layer of organic material, formed by decomposing tree leaves and
wood, which absorbs water. Rainfall can be absorbed by this layer, instead
of becoming superficial run off. Also deforestation generates a weakening of
the soil and favors the erosion, by generating higher quantities of loose soil
to be available for the rainfall to wash them out through surface runoff.
20
Whenever the natural vegetation is removed or the contour of the ground is
altered, without providing some sort of surface protection, the rate of erosion
is greatly increased. The high sediments loads being washed into river
channels and natural streams create propitious conditions for downstream
aggradation processes.
Vegetation is probably the most important physical factor influencing soil
erosion. A good cover of vegetation shields the soil from the impact of
raindrops. It also binds the soil together, making it more resistant to runoff. A
vegetative cover provides organic matter, slows runoff, and filters sediment.
On a graded slope, the condition of vegetative cover will determine whether
erosion will be stopped or only slightly halted. A dense, robust cover of
vegetation is one of the best protections against soil erosion.
In the Guayas River Basin, the lack of an appropriate management of its
resources has allowed the deterioration of its natural conditions, originated
specially by an uncontrolled deforestation of the headwaters of the river, in
the upper regions of the watershed. This process results, as explained
before, in an accelerated erosion of the soil and riverbanks, which in turn
provokes and increment in the amount of sediments being fed to the stream,
a reduction of the cross sectional area of the river due to aggradation
processes, which leads to a diminution of the hydraulic capacity of the river.
According to previous studies, the situation of the Guayas River basin is
critical, given that the annual deforestation rate at the region is very high;
even though its exact values are unknown, it has been said that the
deforestation rate in the Guayas catchment area might reach roughly
250,000 hectares (PIGSA, 2004).
1.6.2.4.
Tide Regime
The Guayas estuary semidiurnal tide regime is fundamental for the
understanding of its sediment transport dynamics, given that once the sea
water enters the estuary and meets the fresh water, which is carrying
21
sediments coming from the rivers; this process causes the flocculation of the
sediment particles and increases the sediment concentration in the water
column, therefore tides are a significant driver of the processes within the
Guayas River system. During the moments of low current speed, the bigger,
newly formed sediment molecules are deposited on the river bed.
1.6.2.5.
Daule – Peripa Dam
The Multi Purpose Jaime Roldos Aguilera scheme comprehends three major
hydraulic projects: the Daule Peripa Dam located on the Daule river,
approximately 140 kilometers north of the city of Guayaquil (Figure A.4 in
Appendices), the Marcel Laniado de Wind Hydroelectric Power Central and
the Irrigation Systems of the Daule Valley. Between them, the dam, with its
6,000,000,000 m3 of water storage, is considered to be the core of the
hydraulic development of the Guayas basin and as such it fulfills a series of
different objectives, some of them are listed below (Espinel and Herrera,
2006):

Water storage for the irrigation of approximately 50000 ha. This
activity requires about 1,000 millions m3.

Water transfers from the Daule River to the Santa Elena province,
for human consumption, irrigation of 42,000 hectares and attend
the water demands for industrial and touristic development.
These activities demand 760 millions m3.

Water supply for the Esperanza and Poza Honda Dam in the
Manabi province.

Water retention corresponding to events of 25 years of return
period for flood control purposes. This activity demands 1,200
millions cubic meters.

Ensure water supply for the city of Guayaquil.

Water supply for hydroelectric generation.

Maintain an appropriate discharge on the river so that the
pollution levels on the Daule River are kept under critical values.
22

Improvement of agricultural productivity.
The Daule Peripa Dam impoundment structure was finished in the year
1998, after 8 years of construction. Apparently its presence has caused
a shift in the hydrologic and sedimentation regimes of the Daule River
due to the regulation of the discharge of the river. During the rainy period
of the year, when the runoff on the catchment area is high, Daule-Peripa
Dam controls the discharge of the river by reducing it, thus causing the
Daule River to transport significantly less water than the Babahoyo
River. But, during the dry months of the year this situation is reversed
and, given the volume of water that has been stored in the dam, the
discharge of the Daule River might be even higher than the one from the
Babahoyo River. It has been mentioned in preceding studies that the
dam has provoked a reduction of the river discharge and a narrowing of
the channel, situation that provides favorable hydraulic conditions for the
formation and evolution of the island, however as it has also been
pointed out in previous research, there’s a lack of information available,
which makes rather difficult to accurately assess the possible effects of
the dam operation on the Daule and Guayas rivers systems, specially on
their sedimentation features.
1.7. Previous Studies
Due to the importance of the Guayas River to the zone surrounding the city of
Guayaquil, some local studies attempts on the river system dynamics and the
island development have been made. The most relevant research on the
subject was presented by the United States Corps of Engineers (USACE) in the
year 2005 in the form of the Guayas River Sedimentation Study report. This
research was supposed to be elaborated in 3 phases (USACE, 2005). Phase I
corresponded to preliminary engineering evaluations, Phase II to the
computational modeling of the river system using the HEC-RAS software and
Phase III to the review of the findings of Phase II. However, due to local
financial difficulties only Phase I was performed and the research was left
23
incomplete and couldn’t provide a better indication of the sediment transport
behavior of the river system.
There’s sufficient bathymetric information on the confluence of the Babahoyo
and Daule Rivers available to allow a local assessment of the temporal
development of the Palmar Island, however no in-depth geomorphic study on a
bigger scale of the Daule, Babahoyo and Guayas river system has been
performed. INOCAR has also undertaken some research on the subject.
However, it has been a general agreement, in most of the previous research,
that there’s a need for further characterization of the island sediments in order
to fully understand the processes that are leading to its accelerated growth and
to try to assess the possible future behavior of both Babahoyo and Daule rivers
at their confluence and that the current available information on river
discharges, sediment loads and sediment production is insufficient to
comprehend the fluvial geomorphic processes that are taking place within the
Guayas River basin.
1.8. Aims of research
As it has been remarked by previous works undertaken on the Guayas river
system and its two tributaries, the rivers Daule and Babahoyo, further
investigation regarding the dynamics of this system is required, especially on
the field of sediment transport conditions and sediment deposition processes.
Because of its location, at the confluence of the rivers Daule and Babahoyo, el
Palmar Island represents a special geomorphologic feature which allows the
investigation of the dynamics of the fluvial system in order to obtain a better
understanding of the variable processes occurring within the river basin,
therefore it has been selected as a model for the development of the research.
The purpose of this study is to present a characterization of the constituting
sediments of the island, with the intention to link its development with the
possible factors affecting the sediment yield on the headwaters of the rivers,
understand the current situation of the river geomorphology and provide the
24
basis for further research on the subject. In order to fulfill those goals the
adequate sampling locations, procedures and strategies were selected.
25
2.
METHODS
2.1. Sampling locations
For the design of the sampling strategy, the total area and shape of the island
was considered, as well as the different zones of it, which can be clearly
identified by a quick visual exploration on the island as described in section 1.7.
For that matter, and in order to obtain representative samples of the soil, it was
determined that four different locations were appropriate. The exact location the
sampling sites was selected on the field, given that the dense vegetation and soil
conditions only permit to work on certain parts of the isle. The approximate
positions of the selected sampling sites are shown in Figure 3 and in Table 7.
Figure 3. Approximate locations of the soil sampling sites on El Palmar Island
Sampling site
1
2
3
4
Coordinates
Latitude
Longitude
2°10'0.10"S
79°52'15.30" W
2°9'55.06"S
79°52'20.27" W
2°9'37.35"S
79°52'19.98" W
2°9'55.94"S
79°52'10.72" W
Table 7. Coordinates for the location of the sediment sample locations on El
Palmar Island
26
Sites 1, 2 and 4 correspond to the older, more stabilized and densely vegetated
part of the island (Figures A.13, A.14 and A.15 respectively in Appendices),
while sampling site 3 is located in the newly form and non-vegetated part of it
(Figure A.16 in Appendices). Sampling one is located roughly to the south end of
the island, samples 2 and 4 correspond to the west and east margin
respectively, the latter is suspected to form part of a possible continuation of the
Babahoyo River channel. Sampling site 3 is on the north end of the island, which
is only accessible during the low tide period of the tidal cycle.
2.2. Sampling Procedures
During the high tide the island gets almost completed covered by water, thus
limiting the possibilities of working on its surface for several hours during the
day. Therefore the scheduling of the island sediment sampling called for the time
regime to be taken into account, so that enough time would be available to
perform the required tasks. Through the use of tide tables it was determined that
the best time to arrive at the island would be in the morning, near the moment of
lowest tide level, in order to allow approximately half a day to work on the island
without inconveniences. For the sampling of the sediments, standard procedures
for soil studies were implemented, using soil core samplers that permit the
extraction of intact soil cores (Figure A.17 in Appendices). Holes were dug,
down to approximately three meters of depth, and the samples that were
extracted, in lengths of 0.60 meters each, were put and kept in sealed sections
of PVC pipes (Figure A.18 in Appendices), prepared specially for that purpose.
Each PVC pipe was clearly labeled in order to allow an easy identification of the
samples in the laboratory. In total, approximately 24 cores were taken from the
island. The samples were identified as shown in Table 8.
27
Sample Label
M1
M2
M3
M4
M5
Sampling Site
2
3
Depth (m)
1
0.00 – 0.60
0.60 – 1.20
1.20 – 1.80
1.80 – 2.40
2.40 – 3.00
0.00 – 0.60
0.60 – 1.20
1.20 – 1.80
1.80 – 2.40
2.40 – 3.00
0.00 – 0.60
0.60 – 1.20
1.20 – 1.80
1.80 – 2.40
2.40 – 3.00
4
0.00 – 0.60
0.60 – 1.20
1.20 – 1.80
1.80 – 2.40
2.40 – 3.00
Table 8. Core identification corresponding to each of the four sampling sites.
The length of the samples, of 0.60 meters each, was selected considering that
the soil texture observed on the field would not produce accurate results in the
laboratory if the samples were of small sizes, since the laboratory procedures
require for the sediments to be dried prior to their analysis and therefore, in
shorter lengths, the soil would get mixed up easily and the results would come
out altered. It was also taken into account that smaller soil samples would not
shown considerable differences in their characteristics to permit an appropriate
interpretation and discussion of the laboratory test results.
2.3. Characterization of sediments
In order to fulfill the objectives of the research, some laboratory testing is
required. With the purpose of obtaining a proper characterization of the islands’
soil structure, through a good identification of the type of sediment being
deposited by the river and its parameters of organic matter content, the following
procedures were selected as the most relevant:

Grain size

Organic Matter and Nitrogen content

Soil PH

Cation exchange capacity (CEC)
28
2.3.1. Grain size (texture)
Soils can be divided into three different phases: a solid, a liquid, and a
gaseous. The solid phase of any superficial soil constitutes approximately 50%
of its volume and is formed of various organic and inorganic particles, all of
which have considerable different sizes and shapes. The proportional
distribution of those different sizes of mineral particles determines the texture
of a given soil, and is considered as one of its basic properties, since it directly
affects the physical properties of the soil such as permeability, strength,
expansivity, water infiltration rate, porosity, fertility etc. Bigger particle sizes
indicate that the soil has more spaces between them, resulting in a more
porous soil. In the other hand, smaller particles sizes will have less space
between them, resulting in a less porous soil, which difficult the passage of
both water and air. Therefore soil classifications have been elaborated based
on the soil’s grain size. The term texture is usually used to represent the
granulometric composition of the soil. Each textural term corresponds to a
certain quantitative composition of sand, the silt and clay. The texture terms
are done without the gravel content; they talk about the fraction of the ground
that is studied in the laboratory of soil analysis and that is commonly known as
fine particles.
The general texture of a soil depends on the proportional particle size
distribution of the different sizes that constitute the soil. The particles are
classified into groups like gravel, sand, silt and clay (as seen in Table 3), but
this classification is not totally arbitrary, as the different soil classes roughly
match changes in properties associated with the differing size fractions. The
gravel particles are bigger than 2 mm of diameter, sand particles have
diameters between 2 and 0.05 mm, are formed predominantly of quartz (SiO2)
with small amounts of silicate-based primary minerals and tend to have
angular rough surfaces; those of the silt have a diameter between 0.05 and
0.002 mm, are also constituted predominantly by quartz with slightly larger
amounts of primary minerals and iron and aluminum oxides and are spherical
29
and more polished. Both silt and sand particles are, from the chemical aspect,
relatively inert. Finally, clay particles are smaller of 0.002 mm, chemically
active and stick together in aggregates that resist erosion and increase soil
porosity. The clay fraction in most temperate region soils is dominated by layer
alumino - silicate minerals. In the humid tropics, where weathering is more
intense, iron and aluminum oxides and hydrous oxides are the dominant
minerals present. In general, the sand particles can identified easily on mere
observation and are rough to the tact. The silt particles are barely visible
without the use of a microscope and posses a flour like appearance when
touched. The clay particles are only visible with use of a microscope and when
they get in touch with water they form a viscous mass.
Soil
Particle diameter (in
particle
millimetres)
Gravel
> 2.0
Sand
0.05 - 2.0
Silt
0.002 - 0.05
Clay
<0.002
Table 9. Soil particle sizes (USDA, 1993).
Based on the proportions of sand, the silt and clay, the texture of grounds is
classified in several defined groups. Some of them are: sandy clay, the silty
clay, the clayey silt, the sandy clayey silt, the clayey mud, the mud, the sandy
silt and the silty sand. The texture of a soil affects some its characteristics to a
great extent, such as its susceptibility to erosion processes, water retention,
productivity, etc. Soils with an elevated percentage of sand usually are
incapable to store sufficient water as to allow the growth of plants and have
great losses of mineral nutrients, which are leached towards the subsoil. The
soils that contain a greater proportion of small particles, for example clays and
silt, are excellent water deposits and lock up minerals that can be used easily.
Nevertheless, the very clayey soils tend to contain an excess of water and have
a viscous texture that prevents, frequently, sufficient ventilation for the normal
growth of the plants.
30
The texture of the soil is linked to the relative quantities of the different particle
sizes. Those quantities are interrelated by a triangular diagram, called the
textural triangle (Figure 4). There are 12 textural classifications as described in
the textural triangle. Gravel (larger than 2.0 mm) is not included in the
definitions of soil texture.
Figure 4. Soil textural classification (Texas Commission on Environmental
Quality, 2005)
This size distribution is associated with many important parameters of the soil,
such as:

Total superficial area

Moisture retention, aeration and permeability

Soil management
The USDA Texture Classes consists on soil descriptions for agricultural, landbased wastewater disposal, and most environmental applications. They were
originally developed with agricultural cropping practices in mind, for example, to
determine the effect of the soil texture on farming. Other texture classification
31
systems have been developed for engineering or other purposes. For example,
 AASHTO:
American
Association
of
State
Highways
and
Transportation Projects, for road engineering purposes
 Unified Soil Classification System, for civil engineering purposes
 Wentworth, for geological and geotechnical studies
Each system has unique terminology to identify the different categories in which
a given soil might fall into.
In the lab, the texture of the soil can be determined using the hydrometer or
pipette methods, after dispersing the aggregates with a chemical dispersant
and agitation (stirring). The hydrometer is a floating measurement device that is
used to determine the density of solutions. A Bouyoucos hydrometer is
calibrated to measure grams of soil per liter of suspension. The rate the
particles fall out of suspension is directly proportional to their size, therefore
when a soil sample is suspended in water, the coarser particles (usually sand)
will settle out first, in approximately 40 seconds, leaving the fine portion of the
soil, like silt and clay, suspended in the water and still contributing to the density
of the suspension. Even though the pipette method is more accurate than the
Bouyoucos hydrometer, the latter is still considered to be one of the simplest
and fastest for analyzing the particle size of soils. A dispersed sample of soil is
thoroughly mixed with water in a tall glass cylinder and allowed to settle. Before
taking readings with the hydrometer, the soil aggregates must be broken down
both physically and chemically. Physical disaggregation is achieved by grinding
the soil sample followed by working it over with a blender. The clay particles
have the tendency to attract one another and must be chemically disaggregated
with sodium hexametaphosphate. This chemical binds to the clay particles,
giving them a negative charge. Negatively charged particles repel each other
and aid in keeping the clay particles in suspension for long periods of time.
After selected settling times, the density of the suspension is measured with the
hydrometer. The basis of the method considers an imaginary plane located
32
some distance below the surface of the soil-water mixture, which means that
when this method is applied, it is found that for a constant height, density
decreases with time. The time required for a given size of particle, say 0.05 mm
in diameter, to fall from the surface of the water to this plane can be calculated.
When this time has elapsed all particles 0.05 mm in diameter and larger
(because these will fall faster) will be below the plane. Immediately above the
plane the concentration of particles smaller than 0.05 mm will be the same as
the concentration of these particles in the entire suspension before
sedimentation began. Measuring the concentration in this plane makes it
possible to calculate the total mass of particles smaller than 0.05 mm,
assuming that the volume of water in the cylinder is known. By selecting
appropriate time periods, the weight of particles smaller than any desired size
limit can be determined.
2.3.2. Organic Matter and Total Nitrogen Content
Organic matter is the constituted by the vast array of carbon compounds in the
soil. Originally created by plants, microbes, and other organisms, these
compounds play a variety of roles in nutrients, water, and biological cycles.
The organic matter (OM) of the soil is formed by biological organic material of
any kind, which can be on or within the ground, alive, dead or in process of
decomposition. Organic matter is a very important component of soil systems;
for simplicity it can be divided into two major categories:
 Biotic OM, such as microorganisms, fungi, bacteria, etc
 Abiotic OM, which is composed by active soil OM (that constitutes
approximately 10 to 15% of the total organic matter) and a stable
fraction of the soil OM, which is composed by different organic acids
and other compounds. The active fraction is actively used and
transformed by living plants, animals, and microbes while the
stabilized organic matter is highly decomposed and stable.
33
Usually the organic matter content increases with the moisture of the soil and
with lower temperatures. Also, fine texture soils are known to have a higher
content of OM. The organic matter suffers a transformation process where
three different stages can be identified:
1. Initial chemical transformation: takes place before the vegetation remains
(e.g. leaf litter) falls to the ground. Consists in the loss of both organic
substances and mineral elements.
2. Accumulation and mechanical destruction: the OM is destroyed by the
action of different factors, thus reducing its size and getting mixed with
the mineral fraction of the soil.
3. Chemical alteration: organic remains in the soil quickly lose their cellular
structure and little by little these remains are disintegrated and they get
completely integrated to the mineral fraction of the soil.
Vegetal remains usually have a high content of carbon, roughly 60% and
nitrogen
represents
a
minor
element,
for
which
plant
roots
and
microorganisms compete. The relation between the carbon and nitrogen
content of a soil is a parameter that evaluates the quality of the organic
remains in the soil. Their biological, chemical and physical properties are
highly correlated with their carbon content. It has been recognized that the
organic matter is the primary source of nitrogen. Even though the original
source of superficial nitrogen comes from the atmosphere, the amount of
available nitrogen required for plant vegetation growth depends on the local
organic production. A site with high production of organic matter will
incorporate more nitrogen amounts to the soil, through the respective
processes of bacterial activity (i.e. decomposition).
The content of OM on the island soil will be determined as a percentage of the
total volume of the samples prior to determination of the soil texture procedure
given that the hydrometer method requires for the separation of the organic
matter fraction of the soil. Since the percentage of organic carbon (OC)
34
present in the soil is directly linked to the OM content, it can be determined
using the formula proposed by Kass (1996):
OC % 
OM %
1.724
The percentage of OC is then used to calculate the carbon/nitrogen (C/N)
dimensionless relation, which can be classified as:
C/N
Classification
< 10
10 - 12
>12
Description
Organic matter is providing a good supply of nutrients to
Low
the soil
Due to the decomposition of organic matter there's normal
Medium
supply of nutrients to the soil
High
Slow supply of nutrients to the soil
Table 10. Classification of a soil C/N relationship (Kass, 1998)
Nitrogen in soils can be found in two major forms: organic and inorganic. For
analytical purposes a third form of nitrogen must be introduced, total nitrogen.
It is defined as the sum of both inorganic and organic nitrogen. Over 90% of all
the nitrogen present in soils is organic and only a small portion is inorganic.
Nitrogen is present in the soil in various compounds, making the process of
determining the total nitrogen content rather complicated. Also the low
concentrations of nitrogen presents further difficulties to the process. Several
methods have been developed to determine the nitrogen concentrations of
soils, some of them are:
 Kjeldahl method
 Dumas method
 Near Infrared Reflectance Spectroscopy (NIRS)
 Direct Distillation method
Among these methods, the Kjeldahl method is the most common one for the
determination of the total N. Even though it was developed almost 180 years
ago, it presents some advantages in comparison with other procedures:

Ease to perform multiple analyses
35

Applicability to low nitrogen samples

It requires small amounts of reagents, making their disposal after use
more convenient.

It requires simple equipment
The total Kjeldahl nitrogen method is based on the wet oxidation of the organic
matter present in the soil using sulfuric acid and a digestion catalyst and the
conversion of organic nitrogen to ammonium, nitrogen. Ammonium is the
determined through spectrophotometric, diffusion – conductivity or distillation
techniques. The method is readily adapted to manual or automated
techniques, since manual methods are usually considered to be time
consuming.
Basically it is divided into 3 different phases:

The digestion phase in which the sample is decomposed by H2SO4
and Na2SO4 and a appropriate catalyst. During the process the
nitrogen and carbon content of the sample is converted into
(NH4)2SO4 and CO2 respectively.

The distillation phase, which consist in the conversion of the NH4+
into NH3 and distilled into H3BO3, or a HCL solution.

The determination of NH4, which is usually done by titration.
Given that some organic compounds, denominated as refractory to Kjeldahl
digestion, cannot be broken down completely during the digestion phase, the
overall accuracy of the whole procedure is highly dependent on the digestion
phase. Because of these difficulties, the method has revised many times over
the years, since its introduction.
The organic matter of grounds is a very important component of the soil
systems. The biological, chemical and physical properties of grounds highly
are correlated with the ground carbon content. Organic matter is the primary
nitrogen source. Although the original source of superficial nitrogen comes
36
from the atmosphere, the amount of nitrogen available for the vegetation
depends to a great extent on the organic production of the location.
2.3.3. Sediment pH
Soil PH quantifies the activity of hydrogen ions in a solution and represents a
measurement of the acidity or alkalinity of a soil. On the pH scale, 7.0 is
neutral, below seven is acid, and above seven is basic or alkaline. A pH range
of 6.8 to 7.2 corresponds to values that can be considered near neutral. It has
been acknowledged that areas of the world, with limited rainfall, typically
possess alkaline soils, while areas with higher rainfall typically have acid soils.
The determination of the soil PH is extremely useful for its characterization,
because it provides a good idea about the solubility and capacity of
assimilation of nutrients by the plants. The pH of soil or more precisely the pH
of the soil solution is very important because this solution carries in it nutrients
such as Nitrogen (N), Potassium (K), and Phosphorus (P) which are needed
by plants, in specific amounts, to grow, thrive, and fight off diseases. Soil pH
influences the solubility of nutrients. It also affects the activity of microorganisms responsible for breaking down organic matter and most chemical
transformations in the soil. Soil pH thus affects the availability of several plant
nutrients.
If the pH of the soil solution is increased above 5.5, Nitrogen (in the form of
nitrate) is made available to plants. Phosphorus, on the other hand, is
available to plants when soil pH is between 6.0 and 7.0. If the soil solution is
too acidic plants cannot utilize N, P, K and other nutrients they need. In acidic
soils, plants are more likely to take up toxic metals and some plants eventually
die of toxicity (poisoning).
The classification of soils, depending on their pH can be made as shown in
Table 11
37
Classification
pH
Extremely acid
3.5 - 4.4
Very strongly acid
4.5 - 5.0
Strongly acid
5.1 - 5.5
Moderately acid
5.6 - 6.0
Slightly acid
6.1 - 6.5
Neutral
6.6 - 7.3
Slightly alkaline
7.4 - 7.8
Moderately alkaline
7.9 - 8.4
Strongly alkaline
8.5 - 9.0
Table 11. Soil classification according to its pH measure.
A pH range of 6 to 7 is generally most favorable for plant growth because most
plant nutrients are readily available. However, some plants have soil pH
requirements above or below this range.
The acidity or alkalinity of the soil is affected by various factors. In natural
systems, the pH is affected by the mineralogy, climate, and weathering.
Management of soils often alters the natural pH due to the utilization of acidforming nitrogen fertilizers, or removal of bases (potassium, calcium, and
magnesium). Soils that possess sulfur-forming minerals are likely to produce
very acid soil conditions when they are exposed to air. These conditions often
occur in tidal flats or near recent mining activity where the soil is drained. The
pH of a soil should always be tested before making management decisions
that might depend on it.
38
The laboratory procedures utilized in the laboratory for the determination of the
soil sample pH included the dilution of the soil in water, with a soil: water
proportion of 1:2.5 and the application of two different extracting reagents to
the solution, the modified Olsen and monobasic calcium phosphate. In general
lines, to determine the pH of soil, it is mixed in a flocculating reagent. The
resulting solution is then treated with a standardized pH indicator that reacts
with the solution to create a different color for different pH values. The colored
solution is then placed in color comparator to assign the correct pH value of
the solution.
2.3.4. Cation Exchange Capacity
Cations are positively charged ions such as calcium (Ca2+), magnesium
(Mg2+), and potassium (K+), sodium (Na+) hydrogen (H+), aluminum (Al3+), iron
(Fe2+), manganese (Mn2+), zinc (Zn2+) and copper (Cu2+). The capacity of a
soil to hold on to these cations is called the cation exchange capacity or CEC.
These cations are held by the negatively charged clay and organic matter
particles in the soil through electrostatic forces (negative soil particles attract
the positive cations). The cations on the CEC of the soil particles are easily
exchangeable with other cations and as a result, they are plant available.
Thus, the CEC of a soil represents the total amount of exchangeable cations
that the soil can absorb. Soils have a CEC primarily because clay particles
and organic matter in the soil tends to be negatively charged. Since the soil as
a whole does not have electric charge, the negative charge of the clay
particles is balanced by the positive charge of the cations in the soil. Organic
matter can have a 4 to 50 times higher CEC per given weight than clay. The
source of negative charge in organic matter is different from that of clay
minerals; the dissociation (separation into smaller units) of organic acids
causes a net negative charge in soil organic matter, and again this negative
charge is balanced by cations in the soil. Because organic acid dissociation
depends on the soil pH, the CEC associated with soil organic matter is called
pH-dependent CEC. This means that the actual CEC of the soil will depend on
39
the pH of the soil. The CEC of a soil with pH-dependent charge will increase
with an increase in pH. The higher the CEC the more clay or organic matter
present in the soil. This usually means that high CEC (clay) soils have a higher
water holding capacity than low CEC (sandy) soils. The lower the CEC, the
faster the soil pH will decrease with time. The CEC of a soil is expressed in
cmolc/kg (centimol positive charge per kg of soil) or meq/100 g (milliequivalents per 100 grams of soil). Both expressions are numerically identical
(10 cmolc/kg = 10 meq/100 g).
The CEC of the soil is determined from an adsorbed amount of index cations,
when passing a solution containing those cations through a soil sample. To
determine the sample’s cation exchange capacity an extracting reagent is
required. For this case ammonium acetate was used and the index cations
were Na, K, Ca and Mg. The CEC of the sample is obtained by the sum of the
extracted index cations.
40
3. RESULTS
After the laboratory tests were performed the following results were obtained.
3.1. Soil Grain Size
The respective laboratory procedures used to determine the island soil texture
gave out the results shown in Table 12
Texture (%)
Classification
Sand
Silt
Clay
M1
6
48
46
Silty clay
M2
32
54
14
Silt loam
P1
M3
54
32
14
Sandy loam
M4
70
18
12
Sandy loam
M5
72
16
12
Sandy loam
M1
22
38
40
Clay loam
M2
22
46
32
Clay
P2
M3
38
40
22
Loam
M4
36
34
30
Clay loam
M5
36
38
26
Loam
M1
32
42
26
Loam
M2
28
42
30
Clay loam
P3
M3
44
30
26
Loam
M4
84
10
6
Sand
M5
86
8
6
Sand
M1
12
42
46
Silty clay
M2
14
48
38 Silty clay loam
P4
M3
26
48
26
Loam
M4
42
38
20
Loam
M5
50
32
14
Loam
Table 12. Soil texture results for the cores taken from El Palmar Island
Sample
Location
Sample
ID
41
3.2. Organic Matter
The laboratory procedures performed on the soil samples showed the following
contents of organic matter, carbon and nitrogen. (Table 13):
Sample
Location
P1
P2
P3
P4
Sample
ID
Organic Matter
content (%)
Nitrogen
content (%)
Carbon
content (%)
C/N
M1
M2
M3
M4
M5
M1
M2
M3
M4
M5
M1
M2
M3
M4
M5
M1
M2
M3
M4
M5
2.6
1.8
1
0.7
0.4
3.8
2.9
1.4
1.7
1.7
2.9
2.6
1.6
0.4
0.7
2.9
2.8
2.1
1.6
1.1
0.34
0.20
0.25
0.17
0.17
0.31
0.22
0.24
0.2
0.22
0.22
0.32
0.34
0.14
0.28
0.25
0.21
0.25
0.22
0.17
1.51
1.04
0.58
0.41
0.23
2.20
1.68
0.81
0.99
0.99
1.68
1.51
0.93
0.23
0.41
1.68
1.62
1.22
0.93
0.64
4.44
5.22
2.32
2.39
1.36
7.11
7.65
3.38
4.93
4.48
7.64
4.71
2.73
1.66
1.45
6.73
7.73
4.87
4.22
3.75
Table 13. Organic matter, nitrogen and carbon contents (in %) of the cores
taken from El Palmar Island
42
3.3. Sediment pH
For the pH laboratory testing, the following results were obtained (Table 14)
Sample
Location
P1
P2
P3
P4
Sample
ID
Ph
M1
M2
M3
M4
M5
M1
M2
M3
M4
M5
M1
M2
M3
M4
M5
M1
M2
M3
M4
M5
6.8
6.2
7
7.4
7.4
6.8
6.4
6.3
7
7
7.3
7.2
7.2
7.1
7.8
7.1
7
6.9
6.9
7.4
Table 14. pH results for the cores taken from El Palmar Island
43
3.4. Cation Exchange Capacity
The following results were obtained for the cation exchange characteristic of the
soil (Table 15)
Sample Location
Sample ID
CEC (meq/100)
P1
P2
M1
M1
41.3
39.6
Table 15. Cation exchange capacity results for the cores taken from El Palmar
Island
44
4. DISCUSSION OF RESULTS
As the obtained laboratory results show, the sediments of the island possess
uniform values of their pH, along space and depth. The pH has a strong influence
in the soil or substrate in several aspects, but the most relevant one for the
purpose of the research, given that it affects the process of island growth and
stabilization, resides on its effects on the availability of nutrients, which means that
the pH controls the amount of nutrients that there is in a soil so that they can be
taken up by the roots of the plants. Extreme pHs might cause the shortage of one
or more nutrients and the plants will show signs of the unfavorable condition. The
problem might be worsened if extreme values of pH are present, such as less than
5, an acid substrate, or higher than 8, very alkaline. In the current case of El
Palmar Island, most of the values, not to say all of them, fluctuate around a value
for the pH of 7, having only a few samples like P1 M1 (6.2), P2 M2 (6.4) and P2 M3
(6.3) inclined to be slightly acid and P3 M5, which has a pH of 7.8, thus making it
slightly alkaline. The neutral nature of the island sediments means that, in relation
to the availability of nutrients, there is a rather favorable condition, so that plant
growth is encouraged and the development and stabilization of the island, due to
the establishment of vegetation, is increased.
The favorable condition for plant growth on the island is also reinforced by the
carbon/nitrogen relation. In all the sampling sites, at all depths, this relation has
values that are classified as “low”. This situation indicates that there’s a very good
supply of nutrients for the existing plants to continue their development. The input
of organic matter to the soil can be explained on two different sources. One is the
islands own vegetation that decomposes on the ground and the nutrients are taken
into the soil. The other source might be organic matter that is provided by the river
flow, in form of suspended sediments. This effect of river input is very likely to be
accentuated by the amount of organic matter that is fed to the river through the
discharge from the drainage system of Guayaquil, especially from its sewage
system that, as it has been said before, has very little treatment before the waters
are poured into the rivers, most likely carrying a very high organic matter load. This
45
process of sedimentation of organic matter into the island further increases the
capacity of the soil to permit the growth of vegetation, thus indirectly favoring the
island growth.
The results of the cation exchange capacity (CEC) tests gave out values greater
than 25, which is the threshold value to indicate a high CEC of the soil. The test
was performed on two different sampling locations, P1 and P3, with opposite
conditions. While P1 is in a vegetated and stabilized part of the island, P3 is in a
“new” part of it, with almost no vegetation. Since the CEC represents the capacity
of a soil with a determined ph to interchange positive ions releasing them and/or
retaining them based on its composition, it is the chemical structure of the soil and
the inputs nutrients what causes that determined ions of certain chemical elements
they can be “transferred” from one element to another. Cations are positive ions
and clays are rich in negative anions, therefore, due to electrostatic attraction a
greater interchange occurs in clayey soils, even though these have serious
problems with their permeability and a tendency for acidity. As El Palmar Island
has shown to have high contents of clay on its soil texture, especially in their most
superficial layers, the high values of the cation exchange capacity could be
explained by the presence of those high percentages of clay in the soil.
Even though the results for the cation exchange capacity of the soil show that on
the superficial layers of the island the soil possesses a high CEC, the organic
matter content of the island sediments is rather low, which is perhaps explained by
the quality of the sediments being fed into the rivers. Both Daule and Babahoyo
rivers are transporting small amounts of organic matter and as a consequence the
deposition of organic matter on the island is minimal. Also, even though there’s a
presence of vegetation in some regions of the island that might represent an
organic matter source, it gets washed away by the action of the flow on the period
of high water level in the river.
The obtained results for the island soil texture show that, on the upper layers of the
substrate until a depth of approximately 1.20 meters, there’s a predominance of
very fine grains particles, such as clay and silt (Figure A.19 and A.20 in
46
Appendices), with the exception of the superficial strata (M1 to M3) from sampling
site P3 which shows a better distribution of the different grain sizes and is
classified as loam or clay loam. The former has the characteristics of being soils
with intermediate characteristics between those of sand and clay. These soils can
be molded, and, with the increment of clay content, the mold becomes firm and
resists deformation under moderate to strong hand pressure. Also, as the clay
content increases, the infiltration rate slows and the soil forms hard clods when dry.
Loamy soils present the best physical and chemical conditions to allow the
establishment and growth of vegetation.
The deeper layers of El Palmar soil are composed, in the case of sampling
locations P1 and P3 by sand, for P2 clay is predominant and in P4 a loamy soil is
present, however the detailed results of the soil texture test show that there’s a
high content of sand (in the order of 50%) in the lower layers of the substrate.
These results show little variation on the composition of the strata between
approximately 1.80 and 3.00 meters, which can be assumed as “older sediments”
of the island, given the depth where they are located. The high percentage of sand
that is present at those depths reinforces the idea that El Palmar Island was
originated from a mid channel sand bar, which started its growth roughly since the
1960s (USACE, 2005). This mid channel bar was used, a few decades ago, for
sand extraction to be used as construction material in the city of Guayaquil and
adjacent zones. These activities served as a sort of control for the growth of ths
isle. Before the construction of Daule - Peripa Dam the Daule River used to
transport
different fine
materials, both in
predominantly sand particles.
suspension and
as
bedload,
Those sediments were fed into the stream by
various tributaries along its path, through natural erosive processes of the river
banks and, during the rainy months of the year, through superficial runoff. The
presence of the deep layers of may also be explained in the effect that the
proximity of the Unidad Nacional Bridge has on the island development. It is
possible that some of the sand deposited on the island might correspond to eroded
bed material from local scour processes at the bridge piers. Also, from the upper
regions of their drainage basin the rivers carried considerable amount of
47
suspended silt and clay, coming from the Manabi province and the northern zone
of the Guayas province. In the other hand, the Babahoyo River transports sand
and finer materials coming from its upper catchment area. Most of those sediments
are deposited by the stream before its confluence, near the city of Guayaquil, with
the Chimbo River (Figure A.20 in Appendices), which in turn contributes with a
significant load of sediments into the Babahoyo River. This load includes very fine
sand silt and clay and is being carried by the river from its headwaters on the
Andes region. After the dam was put into operation, the hydrologic conditions of
the system were altered through the regulation of the discharges coming from the
Daule River. However, the available discharge information on the Daule River does
not permit the adequate analysis of effect of the dam on the river system. The
discharge readings taking at La Capilla gauging station are not sufficient to
elaborate accurate conclusion about this issue. It can be safely stated that, as in
any impoundment structure, most of the sediments that were transported by the
river are now trapped by the dam, provoking that the stream which comes from the
dam discharge, greatly increases its erosive capacity, therefore putting sediments
downstream of the dam more easily into motion. Those suspended sediments,
which are now found in the more superficial or “new” layers of El Palmar Island,
consist mainly in fine particles such as clay and silt and are deposited at the
confluence of the Daule with the Babahoyo River possibly due to the reduction of
flow velocity that is caused by the convergence of the two streams. Given that silt
constitutes a non cohesive material, is put into suspension by the turbulence
caused in the flow due to the presence of the island easier than clay, whose
cohesive forces between its grains create a higher resistance to the erosive action
of the river, thus increasing the content of clay of the island soil. Another source of
clayey sediment can be found in the interaction between the estuary salt wedge
and the operation of the Daule - Peripa Dam. The regulation of the Daule River is
also responsible for a shift in the salinity conditions of the estuary and in the
relation between fresh water and salty water. The salinity conditions directly affect
the sedimentation of suspended clay particles in the estuary. Flocculation takes
place due to the molecular attraction caused by the van der Waals interaction.
48
These forces are not particularly strong, but its intensity is inversely proportional to
the square of the distance between two clay particles, becoming important when
these particles are sufficiently close to each other. In fresh water flocculation does
not take place because the clay particles have negative electrostatic charges and
when they are close to each other, far from allowing the van der Waals forces to
act, particles are repelled for having the same electrostatic charge. In the presence
of salty sea water, when there are free cations, these interact with the negative
charges of clay particles thus neutralizing them, and as a consequence allowing
the van der Waals forces to act, provided that the particles are sufficiently close to
form flocs. The flocculation is an important process in estuaries where the between
fresh and salty water mixture takes place, such is the case of the zone where El
Palmar Island is located, that is under the influence of the effects of the salt wedge,
that in turn is affected by the regulated discharges from the Daule - Peripa Dam.
Even though in the Guayas Sedimentation Study elaborated by the USACE (2005)
it is expressed that the low content of clay in the soil samples taken from the island
could indicate that the flocculation is not a significant process within the estuary it
appears that flocculation does play an important role in the sedimentation
processes in the Guayas River system. The estimated content of clay in the cores
taken for this research can reach values as high as 46% and never lower than 6%,
indicating that there’s a constant deposition of clay particles. While the USACE
report mentioned that clay was only present in low quantities in localized zones of
the island, through the texture analysis for this study it was determined that an
important percentage of clay is present at different locations of the island and at
various depths, perhaps indicating that flocculation has been a constant process
over the years.
In the areas upstream the city of Guayaquil the Daule and Babahoyo Rivers flow
through rural zones which have are use for agricultural purposes, activity which
has seen a marked intensification over the past 20 years. For this reason many
dykes and other containment structures have been built along the path of both
rivers, thus causing that the suspended sediments that are being carried by the
flow cannot be deposited in the natural floodplains of the streams. Then these
49
sediments are transported further downstream and, especially in the case of the
Daule River, are likely to be deposited at the confluence of the streams, where the
flow velocity is severely reduced. However, as it has been pointed out by the
USACE study, where this process has also been mentioned, there’s not enough
available data on the sediment production of the Guayas River basin to allow an indepth analysis on the subject or to make predictions about the effect of the current
agricultural practices in the near future. The sediment transport monitoring within
the Guayas River basin has been very limited over the years and no long term
sampling strategy has ever been designed. It has been mentioned by the USACE
in their Guayas River Sedimentation Study that the only attempt to monitor the
suspended sediment transport of the Daule and Babahoyo rivers was made by
CEDEGE by periodically recording sediment transport data between the years
1971 and 1980. However this attempt failed to produce reliable results due to the
following reason. For the Daule River, the gauging stations were located
appropriately, therefore producing representative spatial data (USACE, 2005). In
the other hand, on the Babahoyo River the gauges only covered a small
percentage of the basin, thus introducing a high uncertainty factor in the recorded
sediment load data, which is greatly relevant because as the Babahoyo River
drains mountainous zones it is expected to carry many times more sediments than
the Daule River and the overall spatial data fails short of being representative of
the Guayas River basin.
Table 16. Sediment production in the Guayas River basin (USACE, 2005)
50
Figure 5. Location of sediment gauging stations in the Guayas River basin
(USACE, 2005)
After the year 1980 CEDEGE did not continue with its suspended sediment
monitoring activities. For that reason there’s not enough available data to evaluate
the sediment transport processes within the Guayas River system, especially when
it comes to the possible influence of the Daule - Peripa Dam on the natural
conditions of the Daule River. The dam was built and put into operation after the
51
year 1980, when the river sediment monitoring has already been suspended for
several years. Because the lack of sediment transport data for the years after the
dam construction it is not possible to make a comparison between the suspended
sediment load being carried by the Daule River before and after the dam.
As in the case of the suspended solids monitoring, the lack of spatial
representative discharge data within the Guayas River basin doesn’t allow a proper
analysis of the effect of the Daule Peripa Dam on the Daule River and on its
geomorphic processes. Missing data on the existent records of the river streamflow
makes it difficult t appropriately interpret the available information. As mentioned in
section 1.4.1.
52
5. CONCLUSIONS
The following conclusions can be taken out from the current research:
 The development and growth of islands in the Guayas River estuary is a
natural occurrence linked to the erosion and sedimentation processes within
the river system. However these processes are being accelerated by human
activities, such as deforestation, agricultural practices and possibly by flow
control structures located in the Daule River, one of its tributaries.
 Under the actual soil characteristics, as observed through the laboratory
results obtained, the pH, cation exchange capacity, nitrogen and organic
matter content of the sediments in the island allows the establishment and
growth of plants, which in turn propitiates the expansion of the isle through a
process of soil stabilization that takes place due to the presence of
vegetation.
The transport of plant propagules, probably from the Daule
River in particular, promotes the colonization of the island by vegetation and
given the characteristics of the substrate, vegetation is easily established,
thus promoting the further development of the island both in height and in
area (Francis, 2006). The development of vegetation on the island appears
to have been favored by the unusual high water levels originated by El Niño
phenomenon. Especially during the 1997 – 98 event, when the Daule River
completely covered the island for long periods of time, facilitating the
deposition of both organic and inorganic sediments of the island surface.
The noticeable accelerated growth of vegetation after this extreme
climatologic event seems to reinforce this theory.
 The soil profiles at different locations of the island, determined with the help
of the soil texture tests in the laboratory, demonstrates that on the deeper
layers of the substrate its texture is constituted primarily by sand, situation
that is explained on the origins of the isle as a mid-channel sand bar. The
superficial strata of the island soil are composed primarily by very fine
sediments, such as silt and clay, which might be originated at different
points along the Guayas River basin, where similar types of soils are found.
53
The accelerated erosion of the soil due to both human activities
(deforestation and agriculture) and extreme hydrologic conditions (El Niño
events) might be causing an increment of the amount of sediment input to
the Daule and Babahoyo Rivers. These two streams are known to transport
both clay and silt as suspended sediments, which are fed into them by their
tributaries. The suspended sediments are transported by the rivers to the
island where they are deposited. An evidence of this process might be found
on the higher island growth rate that has been observed after the El Niño
events from the years 1982 – 83 and 1997 – 98.
 Even though the characterization of the sediments of El Palmar Island has
proven to be useful in the need of understanding the composition of the
island and the local and remote processes that are affecting the dynamics of
the Guayas River system, further and extended research must be
performed, in order to fully comprehend the different interactions of natural
and anthropologic factors that are taking place along the Guayas River
basin.
 When compared to other stabilized islands that exist within the Daule and
Babahoyo rivers system, such as Santay and Mocoli Islands, El Palmar
constitutes a relatively “new” sedimentary structure, therefore providing an
excellent research opportunity to investigate the geomorphology of this
system, taking into consideration the implications of its estuarine
characteristics.
 The relevance of the growth of El Palmar Island relies basically on the
negative effect that this structure might have on the flooding events on the
city of Guayaquil. Therefore it is important to study the dynamics of the
Guayas River system and its tributaries in order to allow an accurate
prediction of the future behavior of this system, taking into account the effect
of the estuarine conditions of the river.
 Due to its location, the island is formed by different factors acting together,
both natural and anthropogenic. Even though the Babahoyo River plays a
fundamental role in the process of island development, it is apparent that
54
the Daule River might be the one contributing with most of the sediment of
the island.
 The lack of spatial representative discharge and suspended sediment data
within the Guayas River basin doesn’t allow a proper analysis of the effect of
the Daule Peripa Dam on the Daule River and on its geomorphic processes.
Missing data on the existent records of the river streamflow makes it difficult
to appropriately assess this issue. The implementation of an extended
network of gauging stations for both sediments and streamflow is required
for a better understanding of the dynamics of this fluvial system.
 The research has allowed a better understanding of the dynamics of the
Guayas River sedimentation processes, through the analysis of the
sediments forming El Palmar Island. However, in order to assess more
accurately the effects of the isle on the fluvial system and its surroundings
and to try to establish its future geomorphologic behavior given the current
conditions, a more in – depth study, including the negative effect that the
occupation of floodplains and the possible need to establish riparian zones
to reduce the input of sediments to the Daule and Babahoyo Rivers, is
required.
55