SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
SECTION 10
LANDFILL INFRASTRUCTURE SYSTEM
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
10.1 DRAINAGE SYSTEM
10.1.1 Introduction
Drainage basins, catchments and watersheds are three synonymous terms that refer to the
topographic area that collects and discharges surface stream flow through one outlet or
mouth. Drainage is the term applied to systems for dealing with excess water. The three
primary drainage tasks are urban storm drainage, land drainage and highway drainage. The
primary distinction between drainage and flood mitigation is in the techniques employed to
cope with excess water and in fact that drainage deals with water before it has reached
major stream channels. Investment in drainage is substantially more than the total
investment in flood mitigation or irrigation. For example for highway projects, about onefourth of the cost of highways is spent on drainage facilities.
In cities, storm water is usually collected in the streets and conveyed through inlets to buried
conduits that carry it to a point where it can be safely discharged into stream, lake, or ocean.
In some instances storm water is percolated into the ground using infiltration ponds. A single
outfall may be used to convey the storm water to the point of disposal or a number of
disposal points may be selected on the basis of the topography of the area.
The design of a drainage project requires a detailed map of the area with a scale between
1:1000 and 1:5000. The contour interval should be small enough to define the divides
between the various sub-drainages within the system. Final design requires even more
detailed maps of those areas where construction is proposed. All existing underground
facilities must be accurately located, together with other structures that might interfere with
the proposed route. If rock is expected near the surface, rock profiles as determined by
borings along the proposed conduit lines are necessary to that pipe layout can be selected
to minimize rock excavation.
10.1.2 Estimate of Flow
The first step in the design of storm drainage works is the determination of the quantities of
water that must be accommodated. In most cases, only an estimate of the peak flow is
required, but where storage or pumping of water is proposed the volume of flow must also
be known. Drainage works are usually designed to dispose of the flow from a storm having
specified return period. It is often difficult to evaluate the damage that results from urban
10-2 | M U A S S I M L A N D F I L L 2 0 1 1
SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
storm water, especially when the damage is merely a nuisance. Hence the selection of the
return period is often dependent on the designer’s judgement. In residential area, there may
be little harm in filling gutters and flooding intersections several times each year if the
flooding lasts only a short time. Return periods of 1 or 2 year in residential districts and 5 to
10 year in commercial districts are all that can be justified for the average city.
Drainage projects almost always deal with flows from ungaged areas, so that design flows
must be synthesized from rainfall data. For urban drainage the most widely used method
has been the rational formula using rainfall of the desired frequency.
The most satisfactory method for estimating urban runoff is by simulation using a computer
program or software. In this approach, flows are simulated throughout the system from
available rainfall data. For adequate definition of the 10 yr event, at least 30 yr of flow should
be simulated. Output is the simulated flow at all key points in the system. From this output
annual flow peaks can be selected and subjected to frequency analysis to define the design
flow at each point. Calibration of the simulation model should be made against the nearest
gaged stream having soil characteristics similar to those of the areas under study.
10.1.3 Hydrologic Losses and Rainfall Excess
Rainfall excess or effective rainfall is that rainfall that is neither retained on the land surface
nor infiltrated into the soil. After flowing across the watershed surface, rainfall excess
becomes direct runoff at the watershed outlet. The graph of rainfall excess versus time is
the rainfall excess hyetograph. The difference between the total observed rainfall
hyetograph and the rainfall excess hyetograph is called the abstractions or losses. Losses
are primarily water absorbed by infiltration with some allowance for inception and surface
storage.
The objective of many hydrologic design and analysis problems is to determine the surface
runoff from a watershed due to a particular storm. The process is commonly referred to as
rainfall-runoff analysis with the objective to develop the runoff hydrograph. Where the
system is a watershed or river catchment, the input is rainfall hyetograph, and the output is
the runoff or discharge hydrograph.
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
a)
SCS rainfall-runoff
The depth of excess precipitation or direct runoff Pe, is always less than or equal to depth of
precipitation P, likewise, after runoff begins, the additional depth of water retained in the
watershed Fa, is less than or equal to some potential maximum retention S. There is some
amount of rainfall Ia, (initial abstraction before ponding) for which no runoff will occur, so the
potential runoff is P-Ia. The SCS method assumes that the ratios of the two actual potential
quantities are equal, that is,
𝐹𝑎
𝑃𝑒
=
𝑆
𝑃 − 𝐼𝑎
(1)
From continuity,
𝑃 = 𝑃𝑒 + 𝐼𝑎 + 𝐹𝑎
(2)
so combining equations 1 and 2 and solving for Pe gives
𝑃𝑒 =
(𝑃 − 𝐼𝑎 )2
𝑃 − 𝐼𝑎 + 𝑆
(3)
Which is the basic equation for computing the depth of excess rainfall or direct runoff from a
storm by the SCS method.
From the study by many small experimental watersheds, an empirical relation was
developed for Ia:
𝐼𝑎 = 0.2𝑆
(4)
So that equation (2) is now expressed as
𝑃𝑒 =
(𝑃 − 0.2𝑆)2
𝑃 + 0.8𝑆
(5)
Empirical studies by the SCS indicate that the potential maximum retention can be
estimated as
𝑆=
100
− 10
𝐶𝑁
(6)
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Figure 10.1: Variables in the SCS method of rainfall abstractions: Ia = initial abstractions, Pe
= rainfall excess, Fa = continuing abstraction, and P = total rainfall.
Where CN is a runoff curve number that is a function of land use, antecedent soil moisture,
and other factors affecting runoff and retention in a watershed. The curve number is a
dimensionless number defined such that 0≤CN≤100. For impervious and water surfaces, CN
= 100; for natural surfaces CN<100. The SCS rainfall-runoff relation 5 can be expressed in
graphical using the curve numbers as illustrated in Figure10.2. Equation 5 or Figure 2 can
be used to estimate the volume of runoff when the precipitation volume P and the curve
number CN are known.
Antecedent Moisture Conditions
The curve numbers shown in Figure 10.2 apply for normal antecedent moisture conditions
(AMC II). Antecedent moisture conditions are grouped into three categories:
AMC I – Low moisture
AMC II – Average moisture condition, normally used for annual flood estimation
AMC III – High moisture, heavy rainfall over preceding few days
For dry conditions (AMC I) or wet conditions (AMC III), equivalent curve numbers can be
computed using
𝐶𝑁(𝐼) =
4.2 𝐶𝑁 (𝐼𝐼)
10 − 0.058 𝐶𝑁 (𝐼𝐼)
(7)
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
and
𝐶𝑁(𝐼𝐼𝐼) =
23𝐶𝑁 (𝐼𝐼)
10 + 0.13 𝐶𝑁 (𝐼𝐼)
(8)
Figure 10.2: Solution of the SCS runoff equations (Mays, 2001)
Soil Group Classification
Curve numbers have been tabulated by the Soil Conservation Service on the basis of soil
type and land use in Table 10.1. The four soil groups in Table 10.1 are described as:
Group A: Deep sand, deep loess, aggregated silts
Group B: Shallow loess, sandy loam
Group C: Clay loams shallow sandy loam, soils low in organic content, and soils usually high
in clay
Group D: Soils that swell significantly when wet, heavy plastic clays, and certain saline soils
10-6 | M U A S S I M L A N D F I L L 2 0 1 1
SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Table 10.1: Runoff Curve Numbers (Average Washed Condition, Ia=0.2S)
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Table 10.1: Runoff Curve Numbers (continued)
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
b)
Rational method
If rainfall intensity remains constant over the time interval required to completely drain a
watershed, then the runoff (intensity) would be equal to the rainfall intensity. From a mass
balance relating rainfall intensity to runoff both intensities can be equated and expressed in
the following formula with suitable conversion factors.
𝑄 = 𝐶𝑖𝐴
(9)
Where
Q = runoff (cm3/s)
i = rainfall intensity (m/s)
CA = net effective area (m2)
The assumptions for use of the formula requires a delineation of the contributing area and
intensity remains constant over the time period required to drain the area (time of
concentration). The contributing area can be related to the characteristics of the watershed
that contribute runoff. For impervious areas that are hydraulically connected (water flow
continuous), runoff and rainfall excess must come from this area. However, other areas may
contribute during heavy or additional rainfall conditions making the contributing area larger.
The impervious area that contributes runoff frequently called the directly connected area
(DCIA). For watersheds that have long travel times, it is almost impossible to have a
constant intensity over that time period. This limits the use of Equation 9 to short time of
travel watersheds. Equation 9 can be restated as the rational formula:
𝑄𝑝 = 𝐶𝑖𝐴
(10)
Where
Qp = peak discharge (cm3/s)
C = runoff coefficient (dimensionless)
i = rainfall intensity (m/s)
A= watershed area (m2)
The basic assumptions for using the rational formula are:
1. The rainfall intensity must be constant for a time interval at least equal to the time of
concentration.
2. The runoff is a maximum when the rainfall intensity lasts as long as the time of
concentration.
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
3.The runoff coefficient is constant during the storm.
4. The watershed area does not change during the storm.
Table 10.2: Runoff Coefficients C Recurrence Interval ≤10 years
c) Simplified Method used in Australia
According to Nelson (1985), estimating of yield could be made by assuming that it is a
percentage of the annual average rainfall. This is regarded as less reliable method but it has
the merits of simplicity and ready availability. It is suitable for small catchment. The
estimated annual runoff from the catchment is calculated from the formula:
Catchment runoff = 100 x A x R x Y litres
(11)
Where: A is the catchment area in hectares, R is the average annual rainfall in millimetres
and Y is the runoff as a percentage of average annual rainfall.
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Table 10.3: Runoff percentage
10.2
DESIGN APPROACH FOR MUASSIM LANDFILL
Due to unavailability of hourly rainfall data from the surrounding areas and the urgency of
the project, USM team has to discard the approach of rainfall analysis using unit
hydrograph. Three methods were initially considered namely SCS rainfall-runoff relation,
rational method and the Australian method. The Australian method was discarded as it is
applicable for localised situation. Thus two methods are used.
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
a) Method 1:SCS rainfall-runoff
No.
1
a)
b)
c)
d)
e)
f)
g)
Design criteria
Location: West of landfill site
Main landfill area
Landfill area toward access road
Balance area of the landfill
(Main part running to the proposed cut off dam)
Total catchment area (Detailed in Figure 10.3)
Hilly catchment area
Balance area of the landfill is divided by 2 (the middle portion of
landfill will recieve half of the estimated run off) (read A1)
The remaining area is divided into ¼ of balance area, (b) (read A2)
Hilly catchment area (5/6 of total hilly catchment area), read H1
Therefore, the total area consists of:
A1
A2+H1
e)
f)
Qpeak determination
Curve Number (CN)
Precipitation
Pe (Depth of precipitation)
Volume of catchment, (A1)
For 3 hours rainfall, Qpeak
h)
i)
Volume of catchment (A2H1)
Qpeak
2
a)
b)
c)
d)
d)
e)
f)
g)
Calculation
Unit
81,000
47,776
623,075
m2
m2
m2
1,250,000
2,126,925
311,538
m2
m2
m2
155769
886,219
m2
m2
311,538
1,041,988
m2
m2
90
0.125
0.120
38346
5.33
m
m
m3
m3/s
128,253
17.81
m3
m3/s
Location: East of landfill site
Landfill area
Catchment area beyond landfill
Hilly catchment area
The landfill area is divided into 2 parts (read A3) (the middle portion
of landfill will receive half of the estimated runoff)
The remaining area is divided into ¼ of the landfill area (c) (read A4)
Hilly catchment area is divided into 2 parts (read H2)
139,149
625,000
485,851
6,9574.5
m2
m2
m2
m2
34,787.25
242,925.5
m2
m2
Therefore, the total area consists of:
A3
A4+H2
69,574.5
277,712.75
m2
m2
0.125
0.120
8348.94
0.77
m
m
m3
m3/s
Qpeak determination
Curve Number (CN)
Precipitation
Pe (Depth of precipitation)
Catchment volume, V (A3)
For 3 hours rainfall, Qpeak
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
h)
i)
33,325.53
3.08
Catchment volume (A4H2)
For 3 hours rainfall, Qpeak
Summary of the design calculation
Location : West of landfill site
A1
A2H1
Qpeak (cm 3/s)
5.33
17.81
Location: East of landfill site
A3
A4H2
Qpeak (cm3/s)
0.77
3.08
m3
m3/s
Notes:
i. Precipitation, P of the landfill area was assumed 6 inch
iii. Rainfall period was assumed lasts for 3 hours.
U drain precast concrete design criteria
By using manning formula, Q = (A × R2/3 × S1/2)/n
Where
Q = flow rate (m 3/s)
A = flow area (m2)
R = wetted perimeter
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
S= channel slope
n = Manning’s roughness coefficient
In order to determine the appropriate size of the u-drain, trial and error method was utilized. Let the
width of the drain, w = 1.5 m, and the height, h = 1.2m
Qpeak
A1
A2H1
A3
A4H2
m3/s
5.33
17.81
0.77
3.08
Location
Middle drain -West of landfill site
Southern and Northern of landfill site (West landfill)
Middle drain – East of landfill site
Southern and Nortern of landfill site (East landfill)
1.
=
=
0.015
0.0066667
=
=
=
1.5
1.2
w*h
m
m
=
1.8
m2
=
=
w + 2h
3.9
m
=
=
A/P
0.4615385
m
Q capacity
=
5.85
m3/s
velocity, V
=
Q/A
(V should larger than 0.6 and less than 4 m/s)
=
3.25
m/s
Let
n
S
w
h
Area, A
Wetted perimeter, P
Hydraulic radius, R
Therefore, Qcapacity>Qpeak
OK
Suitable size will be 2.1 X1.2 m considering medium flow rate
For economical purpose, the drain size of 1.5 X 1.2 m shall be applied to the A1 and A4H2 portions.
2.
n
=
0.015
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
S
=
0.0066667
=
=
=
2.4
1.8
w*h
m
m
=
4.32
m2
=
=
w + 2h
6
m
=
=
A/P
0.72
m
Q capacity
=
18.89
m3/s
velocity, V
=
Q/A
(V should larger than 0.6 and less than 4 m/s)
=
4.37
m/s
Let
w
h
Area, A
Wetted perimeter, P
Hydraulic radius, R
Therefore, Qcapacity>Qpeak
OK
The appropriate size of the drain should be 2.4 X1.8 m considering high flow
rate for A2H1
n
S
=
=
0.015
0.0066667
=
=
=
0.75
0.60
w*h
m
m
=
0.45
m2
=
=
w + 2h
1.95
m
=
=
A/P
0.2307692
m
Q capacity
=
0.92
m3/s
velocity, V
=
Q/A
(V should larger than 0.6 and less than 4 m/s)
=
2.05
m/s
Let
w
h
Area, A
Wetted perimeter, P
Hydraulic radius, R
Therefore, Qcapacity>Qpeak
The suitable size of the drain should be 0.75 X 0.6 m considering low flow rate
for A3
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Summary of SCS rainfall- runoff method
Qpeak
A1
A2H1
A3
A4H2
b)
m3/s
5.33
17.81
0.77
3.08
Location
Middle drain -West of landfill site
Southern and Northern of landfill site (West landfill)
Middle drain – East of landfill site
Southern and Nortern of landfill site (East landfill)
Drain size (m × m)
1.5 X 1.2
2.4 X 1.8
0.75 X 0.60
1.5 X 1.2
Method 2: Rational method
No.
1.
a)
b)
c)
d)
e)
f)
g)
h)
Design criteria
Location: West of landfill site
Main landfill area
Landfill area toward access road
Balance area of the landfill
(Main part running to the proposed cut off dam)
Total catchment area (Detailed in Figure.10.3)
Hilly catchment area
Balance area of the landfill is divided by 2 (the middle portion of landfill
will recieve half of the estimated run off) (read A1)
The remaining area is divided into ¼ of balance area, (b) (read A2)
Hilly catchment area (5/6 of total hilly catchment area), read H1
Therefore, the total area consists of:
A1
A2+H1
Calculation
Unit
81,000
47,776
623,075
m2
m2
m2
1,250,000
2,126,925
311,538
m2
m2
m2
155769
886,219
m2
m2
311,538
1,041,988
m2
m2
311,538
2.02
m2
m3/s
1,041,988
13.02
m2
m3/s
From rational formula
Q = CiA
Q = Peak discharge (m3/s)
C = runoff coefficient
I = rainfall intensity (m)
A = Watershed area (m2)
For A1,
A=
Q for 3h rainfall =
For A2H1
A=
Q=
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
No.
2
a)
b)
c)
d)
Design criteria
Location: East of landfill site
Landfill area
Catchment area beyond landfill
Hilly catchment area
The landfill area is divided into 2 parts (read A3) (the middle portion
of landfill will receive half of the estimated runoff)
The remaining area is divided into ¼ of the landfill area (c) (read A4)
Hilly catchment area is divided into 2 parts (read H2)
Therefore, the total area consists of:
A3
A4+H2
Calculation
Unit
139,149
625,000
485,851
m2
m2
m2
6,9574.5
m2
34,787.25
242,925.5
m2
m2
69,574.5
277,712.75
m2
m2
69,574.5
0.87
m2
m3/s
277,712.75
1.80
m3/s
From rational formula
Q = CiA
Q = Peak discharge (m3/s)
C = runoff coefficient
I = rainfall intensity (m)
A = Watershed area (m2)
For A3,
A=
Q for 3h rainfall =
For A4H2,
A=
Q=
Summary of the design calculation using rational method
Location : West of landfill site
Qpeak (cm 3/s)
A1
2.02
A2H1
13.02
Location: East of landfill site
A3
A4H2
Qpeak (cm3/s)
0.87
1.80
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Summary for maximum dishcarge flow rate
Qpeak
A1
A2H1
A3
A4H2
m3/s
2.02
13.02
0.87
1.80
Location
Middle drain -West of landfill site
Southern and Northern of landfill site (West landfill)
Middle drain – East of landfill site
Southern and Northern of landfill site (East landfill)
U drain precast concrete design criteria
By using manning formula, Q = (A × R2/3 × S1/2)/n
Where
Q = flow rate (m 3/s)
A = flow area (m2)
R = wetted perimeter
S= channel slope
n = Manning’s roughness coefficient
In order to determine the appropriate size of the u-drain, trial and error method was utilized. Let the
width of the drain, w = 1.5 m, and the height, h = 1.2m
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
n
S
=
=
0.02
0.006667
=
=
=
2.1
1.8
w*h
m
m
=
3.78
m2
=
=
w + 2h
5.7
m
=
=
A/P
0.66
m
Q capacity
=
15.65
m3/s
velocity, V
=
Q/A
(V should larger than 0.6 and less than 4 m/s)
=
4.14
m/s
Let
w
h
Area, A
Wetted perimeter, P
Hydraulic radius, R
Therefore, Qcapacity>Qpeak
OK
Suitable size of the drain should be 2.1 X1.8 m considering high flow rate contributed from large
area for A2H1
n
S
Let
w
h
Area, A
Wetted perimeter, P
Hydraulic radius, R
Q capacity
velocity, V
=
Q/A
(V should larger than 0.6 and less than 4 m/s)
=
=
0.015
0.006667
=
=
=
1.5
0.75
w*h
m
m
=
1.125
m2
=
=
w + 2h
3
m
=
=
A/P
0.375
m
=
3.184
m3/s
=
2.83
m/s
Therefore, Qcapacity>Qpeak
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
The suitable size of drain should be 1.5 X 0.75 m considering medium flow
rate for A1 and A4H2.
n
S
=
=
0.015
0.006667
=
=
=
0.9
0.6
w*h
m
m
=
0.54
m2
=
=
w + 2h
2.1
m
=
=
A/P
0.257143
m
Q capacity
=
1.189
m3/s
velocity, V
=
Q/A
(V should larger than 0.6 and less than 4 m/s)
=
2.20
m/s
Let
w
h
Area, A
Wetted perimeter, P
Hydraulic radius, R
Therefore, Qcapacity>Qpeak
Suitable size will be 0.9 X 0.6 m considering low flow rate for A3
Summary of rational method
Qpeak
A1
A2H1
A3
A4H2
m3/s
2.02
13.02
0.87
1.80
Location
Middle drain -West of landfill site
Southern and Northern of landfill site (West landfill)
Middle drain – East of landfill site
Southern and Northern of landfill site (East landfill)
Drain size (m X m)
1.5 X 0.75
2.1 x 1.8
0.9 X 0.6
1.5 X 0.75
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Table 10.4: Comparisons between two methods for the perimeter drain size determination
Qpeak
A1
A2H1
A3
A4H2
Location
Middle drain -West of landfill site
Southern and Northern of landfill site (West landfill)
Middle drain – East of landfill site
Southern and Nortern of landfill site (East landfill)
Method
SCS
Rational
1.5 X 1.2
1.5 X 0.75
2.4 X 1.8
2.1 x 1.8
0.75 X 0.60
0.9 X 0.6
1.5 X 1.2
1.5 X 0.75
The detail cross section of box culvert is given in Appendix AO.
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Figure 10.3: Catchment area
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
10.3
ACCESS ROAD SYSTEM
In this proposed design, an access road will be constructed to serve the leachate pumping
well and maintenance of gas ventilation systems. It covers the whole sections, the main
landfill and the east side of the landfill. The design is based on conventional standard that
consists of premix (top layer), crusher run and sub base. Details of cross section and the
access road system layout in the landfill are shown in Figures 10.4 and 10.5, respectively.
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Figure 10.4: Proposed cross section of access road
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SUSTAINABLE CLOSURE DEVELOPMENT PLANNING AND DESIGN FOR THE MUASSIM LANDFILL
Figure 10.5: Proposed layout of access road
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