Rainwater and Urban Design Conference 2007
Sydney, 21 - 23 August, 2007
Water Quality and Maintenance Costs of Constructed Waterbodies in
Urban Areas of South East Queensland.
M.L. Bayley1, D. Newton 2
Wet Feet Aquatics, [email protected]
2
South East Queensland Healthy Waterways Partnership
1
Abstract
Artificial waterbodies are a popular feature of urban development in South East Queensland (SEQ) and across
Australia. However, anecdotal reports from local government officers within SEQ indicate that many of these
waterbodies regularly fail to meet their design water quality objectives. This often results in poor ecological
function and the degradation of the waterbody. The costs to prevent such problems and/or restore degraded
systems are thought to be substantial, but are not well documented in the SEQ region. In late 2006, the South
East Queensland Healthy Waterways Partnership initiated a survey of local governments in SEQ to collect
available data on water quality and maintenance costs of existing artificial waterbodies in urban areas.
Responses from 6 of the 18 local governments in the region provided data on 83 urban waterbodies with a
combined total surface area exceeding 490 ha. Nutrient concentrations in existing waterbodies were found to
exceed relevant water quality objectives, particularly for phosphorus. This resulted in elevated algal biomass
and prolific macrophyte growth in many of the waterbodies. In the 2005/06 financial year, three of the surveyed
councils spent an estimated total of nearly $4.8 million on maintenance activities for 20 constructed urban
waterbodies. About two-thirds of this amount was spent on routine maintenance and the remainder on corrective
maintenance required to restore deteriorated or malfunctioning components of a waterbody. Management of
aquatic vegetation was identified as the most significant routine maintenance cost.
Introduction
Constructed urban waterbodies (commonly referred to as ‘lakes’) are a popular feature of
urban development in many countries, including Australia. Such waterbodies may be created
for a variety of social, economic and environmental reasons. From the perspective of land
developers, urban waterbodies can provide scenic amenity as well as recreational
opportunities and wildlife habitat, which commonly lead to higher land values in surrounding
areas.
Whilst constructed urban waterbodies may confer many benefits upon their local
communities, maintenance of acceptable water quality over the long term has proven to be a
significant challenge. Published limnological information on urban waterbodies is relatively
limited. However, a number of authors (Duncan 1998; Statwell and Cordery 1998; Butler and
Davies 2000; Morris et al. 2003; Walsh 2004) have identified the following potential water
quality and management issues in urban waterbodies:
• excessive algal growth,
• cyanobacteria blooms,
• excessive macrophyte (water plant) growth, and
• high turbidity levels.
Of the above issues, excessive algal and macrophyte growth appear to be the most
problematic and prolific issues within urban waterbodies. In the USA, 80% of all urban
waterbodies are classed as either eutrophic or hypereutrophic since they receive higher
phosphorus (and nitrogen) loads than waterbodies within non-urban catchments (Mitsch and
Gooselink 2000). For this reason, algal populations within urban waterbodies can be highly
productive, rapidly reaching bloom-like proportions. In many urban lakes, cyanobacteria
blooms are common, creating both public and environmental health issues (Reynolds 1995;
Sommarunga and Robarts 1997; Ferber et al. 2004).
The subtropical climate of South East Queensland (SEQ) has some specific characteristics
that increase the risk of water quality problems within storages that collect urban stormwater
runoff. These characteristics include:
•
Relatively high temperatures that increase the productivity of algae, macrophytes and
cyanobacteria. Over an annual cycle, restricted productivity due to low temperature is
almost non-existent.
•
High inflow variability due to the seasonality of rainfall and the occurrence of highintensity storms with substantial inter-event periods. Under these conditions, impounded
water is not regularly flushed, potentially resulting in the depletion of dissolved oxygen
through algal and bacterial processes.
After the initial construction and establishment period of artificial urban waterbodies (of the
order of 3 to 10 years), ownership typically passes to a local government authority, which
then becomes responsible for all maintenance activities associated with the waterbody.
Anecdotal evidence from local government officers in SEQ indicates that water quality within
urban waterbodies is typically poor, resulting in a substantial maintenance burden. However,
very limited information is presently available to characterise the observed water quality in
the region’s urban waterbodies, or to provide an estimate of the most likely maintenance
requirements and costs. This paper summarises data on water quality and maintenance costs
for urban waterbodies, collected from local governments in SEQ.
Data collection
In October 2006, a project steering committee of local government representatives, hosted by
the South East Queensland Healthy Waterways Partnership, initiated a survey of local
governments in SEQ to obtain information on:
•
The number and physical characteristics of urban waterbodies within their jurisdiction,
•
Observed water quality within these waterbodies,
•
Actual or estimated expenditure on maintenance activities for these waterbodies.
To focus the study on major urban water features, data was requested only for waterbodies
with a surface area of greater than 0.5 ha (5,000 m2) and substantially urbanised catchments.
This eliminated water supply dams and most stormwater treatment devices (such as
sedimentation basins and constructed wetlands) as well as a very large number of small
impoundments, such as golf course ponds and in-stream pools, from the investigation. Tidal
systems were not included in the study. Using these criteria, data was obtained on 83
waterbodies across 7 of the 18 local government areas in SEQ. It is noted that this is unlikely
to represent all of the waterbodies in the region, since some waterbodies are in private
ownership, whilst some local governments had minimal data on relevant waterbodies, or
inadequate resources to respond to the data request.
Data analysis
Physical characteristics of urban waterbodies
Table 1 displays the physical characteristics of SEQ waterbodies captured within the survey:
•
The median surface area of artificial urban waterbodies in SEQ is 2.2 ha. The mean
size of waterbodies within Caloundra City Council and Gold Coast City Council is
substantially greater than the other council areas – exceeding the 90th percentile of the
entire data set.
•
Local government in SEQ is currently responsible for the management of urban
waterbodies with a total surface area of more than 490 ha.
•
•
•
•
•
The median volume of the 14 urban waterbodies with relevant data is 53.2 ML. Most
of these urban waterbodies hold a maximum of 25 to 175 ML.
The mean depth of artificial urban waterbodies across SEQ is 3.0m.
The waterbody perimeter length was highly variable, ranging from 290m to 20,000m.
Approximately 75% of the waterbodies captured within the survey have a perimeter
length of between 500 and 1,000m.
The calculated mean catchment area (523 ha) feeding artificial waterbodies within
SEQ was substantially higher than the calculated median (162 ha).
The reported mean proportion of developed urban land within waterbody catchment
areas was 71%.
Table 1: Physical characteristics of artificial urban water bodies within SEQ (Blanks cells indicate no
data available).
Surface area (ha)
Local
Govt.
Logan
City
Pine
Rivers
Shire
Maroochy
Shire
Gold
Coast City
Caloundra
City
Brisbane
City
Redland
Shire
SEQ total
Total
N
Mean
Median
Total
N
Mean
Median
Total
N
Mean
Median
Total
N
Mean
Median
Total
N
Mean
Median
Total
N
Mean
Median
Total
N
Mean
Median
Total
N
Mean
Median
Sum
10
3.7
2.3
37
17
2
1.4
34
20
1.6
1.5
32.2
11
21.4
7
235
7
15.4
4
108
6
6.97
7.95
41.8
2.00
1.15
2.30
73
6.7
2.2
490
Water
depth
<50cm
Water
depth
>3m
Full
volume
(ML)
Depth (m)
Max
4
2
2
7
5
32.9
15.0
164.5
1
33
33
33
9
64
31
579
2
6021
6021
12042
3
4
4
12
3
1.6
1.5
4.9
2
346
346
692
1
5
5
5
1
3.9
3.9
3.9
9
5.6
5.5
50.5
4
7.3
8.0
29.0
7
2.6
2.0
18.5
4
2.9
3.0
11.7
7
3
2
19
8
21.2
5.7
169.4
14
953
53.2
13346
26
4.6
3.9
118
Mean
1
1.0
1.0
1.0
10
3.5
3.3
35.2
7
3.4
3.0
23.5
4
1.6
1.5
6.2
22
3.0
2.8
65.9
Perim.
length
(m)
Total
catch.
area (ha)
% catch.
urban
10
1262
895
12620
17
659
576
11205
20
703
715
14077
11
3635
1100
39990
8
837
42.5
6702
17
100.2
75.63
1704.5
9
184.6
184
1662
10
1486
330
14860
10
90.8
100
-
4
1582
1614
6328
2
1669
5
138.8
113
694
3
100
100
-
49
523
162
25623
38
70.8
80
2692
3339
64
1368
783
87559
8
62.5
70
17
57.8
60
-
Water Quality and Treatment Measures
Information requested as part of the survey included data on water quality, as well as water
quality treatment measures implemented for the waterbodies. Water quality treatment
measures were identified as either pre-treatment of inflows (using, for example, constructed
wetlands, gross pollutant traps or bioretention systems), or in-situ treatment (such as
mechanical destratification, aeration or recirculation). The survey results indicated that only
14 of the 83 waterbodies included pre-treatment measures. In-situ treatment devices were
provided for waterbodies within Gold Coast City (occurring in 6 of the 11 waterbodies) and in
Maroochy Shire (occurring in 3 out of 20 waterbodies).
From the available data, there was no evidence that waterbodies with any type of treatment
measures in place had better water quality than others. However, due to the small amount of
data available and the wide range of potential issues affecting the installation and maintenance
of these treatment measures, it should not be concluded that pre-treatment or in-situ treatment
does not measurably improve water quality.
Water quality data was obtained for 29 of the identified SEQ urban waterbodies. The
collected data is summarised in Table 2. Pine Rivers Shire Council provided water quality
data for 15 waterbodies, Gold Coast City Council provided data for 7 waterbodies, and
Maroochy Shire Council provided data for 5 waterbodies. Brisbane City, Logan City and
Caloundra City Councils each provided water quality data on one waterbody.
The information provided on water quality did not include the timing of sampling relative to
rainfall events. Whilst rainfall events would have some impact on water quality, the large
number of samples represented in the data would provide a reasonable long-term average of
expected water quality. No quality assurance of sampling methods or analysis techniques,
beyond that undertaken by local governments in the collection of their data, was undertaken
for this study.
Based on the regional guidelines for physico-chemical parameters in lakes and reservoirs in
South East Queensland (see Table 2.5.1.1, EPA 2006), the region’s waterbodies met turbidity
guidelines just under 90% of the time. For total nitrogen (TN), the reported mean of 0.83 mg
L-1 exceeded the guideline value of 0.35 mgL-1 (EPA 2006). The mean total phosphorus (TP)
concentration across the entire data set (0.11 mgL-1) was an order of magnitude higher than
the guideline value of 0.01 mgL-1. Only two waterbodies within Gold Coast City (Pizzey
Park Lake and Lake Hugh Muntz) ever met TP guideline values. All other identified
waterbodies within SEQ exceeded TP guidelines.
Phytoplankton biomass (as measured
using Chlorophyll a) across all waterbodies at all sampling times was above the 5 µg L-1 SEQ
water quality guideline (EPA 2006). Chlorophyll a data was based on only seven water
bodies, six of which lie within Gold Coast City.
The mean dissolved oxygen (DO) saturation for all these waterbodies was 86.9%, 3.1% below
the lower limit of the SEQ water quality guidelines. Note however that spot DO saturation
readings are limited in their usefulness for defining the water quality of a waterbody, since
DO varies naturally over any 24hr period. This is due to the natural diurnal variability in the
productivity of algal and bacterial communities within a waterbody consuming and/or
producing oxygen.
Further anecdotal comments received from some of the participating local government
officers included:
• The presence of large bird populations were perceived to have a negative impact on
water quality;
• Cyanobacteria blooms were noted to occur in some waterbodies;
• Odour issues were identified in many of these waterbodies.
Table 2: Summary of water quality data of identified waterbodies.
Turbidity (NTU)
TN (mg L-1)
TP (mg L-1)
Chlorophyll a (µg L-1)
DO (%)
No.
waterbodies
with data
9
13
28
7
29
Total no.
of samples
Min.
Max.
Mean
Std
Dev
Guideline
Value
1011
354
1263
909
778
0.87
0.34
0.01
6
36.60
27.3
3.25
0.34
50
125.0
6.2
0.83
0.11
18.4
86.94
8.5
0.79
0.08
17.9
22.31
1 - 20
0.35
0.01
5
90 - 110
Maintenance activities and costs
Maintenance cost data was provided for 20 of the 83 waterbodies identified in the survey.
Data on maintenance activities and costs was supplied by Brisbane City, Maroochy Shire and
Gold Coast City Councils. One of the difficulties encountered by local government officers
in collating relevant data was that maintenance costs are often tracked against activities or
regions, rather than against a specific waterbody.
Maintenance activities can be divided into routine maintenance and corrective
maintenance. Routine maintenance consists of regular tasks or expenses necessary to
operate and maintain an acceptable level of functionality of the system. For example,
vegetation harvesting, cleaning of pre-treatment devices or running costs for an artificial
recirculation system. These are costs that can be anticipated on a regular cycle. Corrective
maintenance includes works required to restore deteriorated or malfunctioning components of
the system. For example, repair of revetment walls or installation of an in-situ treatment
system. These costs are more difficult to estimate and can often involve substantial
expenditure.
Table 3 outlines the type of maintenance procedures undertaken on the 20 identified
waterbodies across SEQ in the 05/06 financial year, as well as actual or estimated
maintenance costs. As shown in Table 3, the total maintenance cost (including both routine
and corrective maintenance costs) is highly variable, ranging from only $1200 for Oxford
Park Lake to $1,585,500 for Rosser Park Lake.
Major corrective maintenance activities were undertaken by all councils submitting cost data.
These activities included major works at the Mapleton Lilyponds in Maroochy Shire, Rosser
Park in Gold Coast City, and Einbumpin Lagoon in Brisbane City. Based on the analysis of
the maintenance data, the management of vegetation within waterbodies and corrective
maintenance procedures were the two most significant maintenance activities undertaken by
councils.
The total sum of routine and corrective maintenance costs for the 2005/06 financial year for
the 20 identified waterbodies was $4,755,000. As shown in Table 4, routine maintenance of
the relevant urban waterbodies in 2005/06 totalled just over $3 million dollars. Corrective
maintenance procedures over the same period totalled about $1.7 million. Based on the
surface area of maintained urban waterbodies (268 ha), the total cost of routine maintenance
procedures per unit area is about $11,300 per ha for 2005/06. Corrective maintenance costs
over this period totalled $6,500 per ha for the 05/06 annual period (Table 4). Note that unit
area costings should be considered with caution, since maintenance expenditure is dependent
upon a wide range of factors and thus highly non-linear.
The costs presented in Table 3 do not account for the adequacy of the maintenance program.
Based on feedback from local government officers during the data collection process, it is
likely that many of these waterbodies are “under-maintained”, with maintenance costs
deferred until water quality or some other element of the system deteriorates to a level which
generates community complaints. Restoration of such degraded (typically eutrophic) systems
was consistently identified as being costly, with significant uncertainty around the likely
success of any proposed corrective maintenance program.
Table 3: Cost of maintenance activities for 20 urban waterbodies in SEQ during 2005/06.
1
2
Lake-Dalton Dr
4
Lakeshore Ave Park
7
Mapleton Lillyponds
20
Nelson Park
12
Allora Gardens
4
Kolora Park
6
3
Cost ($k) for Maintenance Activity *
5
6
7
8
9
10a
4
750
250
1020
12
4
50
9
16
Robina West
20
6
15
Total
($k)
24
10
100
12
10
Robina South
Rosser Park
11
4
7
Bli Bli Wetland
Clear Island Waters
10b
15
150
350
200
900
.
1
7
.
56
2
27
5
38
5
170
8
9
48
6
520
23
9
16
20
40
10
1586
15
6
241
218
621
Lake Lomandra
15
0.5
5
Pizzey Park
10
7
10
27
Lake Hugh Muntz
5
6
5
16
Waterhen Lake
10
10
Oxenford Park Lake
Lake Santa Cruz
1
4
Einbumpin Lagoon
1
2
6
300
Lakewood
48
Forest Lake
52
N
18
Minimum
230
530
36
8
5
12
8
3
3
1
3
4
11
1
8
4
7
8
5
12
10
0.5
7
Maximum
100
300
750
250
350
900
48
84
20
105
20
230
6
5
2
1
20
5
15
2
9
20
1
7
20
520
23
105
20
1586
238
Mean
20
152
319
128
137
308
10
7
8
169
12
41
20
Median
10
150
200
250
50
7.5
6
7
6
105
8
9
20
32
Total
351
457
958
255
412
925
111
7
56
1011
69
123
20
4755
* Column title key:
1 – Vegetation management 2 – Desilting 3 – Corrective Maintenance 4 – Decommissioning / Disposal 5 – Management
Plans 6 – Edge treatments 7 – Water quality monitoring 8 – Bathymetry 9 – Management of animal pests 10a – In situ
treatment capital costs 10b – In situ Treatment ongoing costs 11 – Research 12 – GPT’s
Table 4: Summary of total routine and corrective maintenance costs for 20 urban waterbodies within
SEQ during 2005/06.
Maintenance Type
Total Cost ($)
Cost per ha
Surface Area ($)
Routine maintenance
$3,025,000
$11,300
Corrective maintenance
$1,730,000
$6,500
Total (Routine & corrective maintenance)
$4,755,000
$17,800
Note: Total surface area of costed waterbodies = 268 ha.
Conclusions
Data provided by SEQ councils indicates that local government in this region is responsible
for the maintenance of at least 83 constructed urban waterbodies that have a surface area of
more than 0.5 ha. The median surface area of these waterbodies is 2.2 ha, with a combined
total surface area exceeding 490 ha.
Mean TN and TP concentrations in urban waterbodies across the region are 0.83 mgL-1 and
0.11 mgL-1 respectively, both of which substantially exceed guideline concentrations for
acceptable water quality. Whilst stormwater inflows are the dominant source of nutrient
compounds in urban waterbodies, the behaviour and ultimate fate of nutrients within the water
column will ultimately depend on the trophic links within the system. An oversupply of
nutrients, relative to the assimilative capacity of the system, will most likely result in the
degradation of water quality, either through algal blooms, cyanobacteria blooms or excessive
macrophyte growth. This appears to be the case in many of the artificial urban waterbodies in
SEQ. Since most Australian freshwater aquatic environments tend to be phosphorus limited
(Davis and Koop 2006), reducing the supply of phosphorus to a waterbody may have a greater
water quality benefit than reducing the nitrogen supply.
In the 2005/06 financial year, Brisbane City, Maroochy Shire and Gold Coast City spent an
estimated total of nearly $4.8 million on maintenance activities for constructed urban
waterbodies. Almost two-thirds of this amount was spent on routine maintenance (such as
vegetation harvesting and cleaning of pre-treatment devices) and the remainder on corrective
maintenance required to restore deteriorated or malfunctioning components of the system.
Management of aquatic vegetation was identified as the most significant routine maintenance
cost.
The available data (though limited) provides an indicative routine maintenance cost of the
order of $11,000 per ha per year for constructed waterbodies. Applying this indicative unit
rate across all waterbodies in the region, the total annual cost of routine maintenance is of the
order of $5.4 million. Corrective maintenance activities are a significant additional cost.
Since most waterbodies do not meet relevant water quality objectives, it is likely that this
underestimates the full cost that would be required to maintain waterbodies at an acceptable
water quality standard in the long term.
The data collected during this study, though limited, provides some insight into the magnitude
of maintenance issues associated with constructed urban waterbodies, as well as key areas of
research and management action to improve system performance and reduce maintenance
costs in the long term. Key research and management issues that can be inferred from the
results of the study include the need for:
•
Ongoing research to improve the understanding of nutrient cycling processes and
limnological behaviour of typical urban waterbodies under local conditions. The USEPA
are currently undertaking such a research program in the USA (the “National Lakes
Inventory”, USEPA 2007).
•
Development of reliable remediation strategies for eutrophic systems. Waterbody
remediation guidelines would provide an increased level of confidence that a proposed
remediation strategy would achieve a defined level of improvement in water quality at
minimum cost.
•
Development of locally-relevant design and maintenance guidelines for urban
waterbodies. These guidelines would ensure that any new systems are designed,
constructed and maintained to prevent eutrophication.
•
Implementation of a regionally consistent protocol for collection of data on maintenance
activities and costs for constructed urban waterbodies. The data generated through this
•
process would improve the ability of local government to plan the allocation of
maintenance resources.
Local government to consider options to ensure that a financially sustainable management
regime is implemented for any proposed new urban waterbodies.
Acknowledgements
The authors gratefully acknowledge Maroochy Shire Council for providing funding to
undertake this study, as well as the project steering committee and numerous council officers
who researched and collated the various types of data requested.
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