U.S. Army Corps Of Engineers Releases Civil Works Strategic Plan
Washington /PRNewswire-USNewswire/ – The U.S. Army Corps of Engineers (USACE) today released its “Sustainable Solutions to America’s Water Resources Needs: Civil Works Strategic Plan 2014-2018” that articulates five goals that will guide USACE into the future.
“This strategic plan presents USACE’s commitment to responsibly develop the Nation’s water resources, while protecting, restoring and sustaining environmental quality. USACE is dedicated to learning from the past and adapting the organization to ensure the U.S. enjoys a prosperous and sustainable future,” said Steven L. Stockton, USACE director of Civil Works.
USACE has been a leader in developing and managing water resources in the United States for more than 230 years and is committed to continuing the advancement of its Civil Works Program through the five strategic goals presented in the Strategic Plan. Those goals are to:
Transform the Civil Works Program to deliver sustainable water resources solutions through Integrated Water Resources Management;
Improve the safety and resilience of communities and water resources infrastructure;
Facilitate the transportation of commerce goods on the Nation’s coastal channels and inland waterways;
Restore, protect, and manage aquatic ecosystems to benefit the Nation; and
Manage the life-cycle of water resources infrastructure systems in order to consistently deliver sustainable services.
The Strategic Plan will guide USACE mission accomplishment and translate the organization’s vision into reality. The plan lays out an overarching Integrated Water Resources Management (IWRM) strategy that embraces a holistic focus on water resources challenges and opportunities that reflects development and management of water, land and related resources. The IWRM approach is supported by six cross-cutting, overarching strategies:
Systems Approach – Water resources planning and management should be watershed-based using systems analysis methods and tools to understand, assess and model the interconnected nature of hydrologic watersheds/systems, the economic and ecologic systems they support, and identify and evaluate management alternatives and holistic inputs and outputs.
Collaboration and Partnering – Build and sustain collaboration and partnerships with other agencies and organizations at all levels to leverage authorities, resources, talent, data, and research.
Risk-Informed Decision Making and Communication – Develop and employ risk- and reliability-based approaches that incorporate consequence analysis, especially risk to humans; identify, evaluate, and forestall possible failure mechanisms; and quantify and communicate residual risk.
Innovative Financing – Seek innovative arrangements such as public-private partnerships, revised funding prioritizations, and other appropriate funding mechanisms to develop and sustain water resources infrastructure.
Adaptive Management – Use adaptive management, a life-cycle decision process that promotes flexible decision making that can be adjusted in the face of risks and uncertainties, as outcomes from management actions and other events become better understood through monitoring and improved knowledge.
State-of-the-Art Technology – Embrace new and emerging technology and research that improve infrastructure resiliency, assist in updating design criteria, improve approaches toward planning and design, and support smart decisions.
“Sustainable Solutions to America’s Water Resources Needs: Civil Works Strategic Plan 2014-2018” is available on the web at
Report for Potential Use of Stormwater in the Perth Region
The Department of Water (DoW) is investigating the potential for stormwater harvesting of the drainage network within the Perth metropolitan and Peel regions as a source of potable or non-potable water. The purpose of this study was to estimate the quantity of available stormwater, to identify harvesting options and to present a preliminary indication of geographical locations within the metropolitan region that may be suitable for surface or groundwater storage of stormwater. Discharge estimates were based on a combination of data and catchment modelling.
The median annual discharge of stormwater from the Perth and Peel Metropolitan regions was estimated as 120 GL with approximately 67% from the Swan-Canning catchment (exclusive of Avon and Helena rivers; and Ellen, Jane and Susanah brooks), 16% from the coastal Main Drains (Carine, Herdsman and Subiaco) and 17% from the Peel’s Main Drains. This stormwater volume is equivalent to approximately 2 Mundaring Weirs at full storage capacity (63.6 GL) or 2.5 desalination plants (45 GL). This is also greater than the potential volume from rainwater harvesting of the region’s residential roofs.
Strategies for harvesting and storage of this potential drainage resource are dependent on the hydrology of the study area. In two Main Drains (Bayswater and Yule Brook) approximately 40-50% of the winter discharge is generally comprised of baseflow, and the remaining 50-60% is stormwater runoff.
Harvesting of stormwater events requires an opportunistic approach such as filling basins (i.e. underground voids, storage basins). In contrast, stormwater harvesting and storage of winter and spring baseflows can be achieved through relatively constant pumping of these waters into the aquifer.
Alternative strategies such as stormwater aspects of Water Sensitive Urban Design (WSUD) and modification of the Main Drain invert (or bottom) levels aim to increase the fraction of the stormwater runoff volume transferred and maintained in the groundwater. For example, greater infiltration and a decrease in the direct loss of stormwater via the drainage network occur via the implementation WSUD principle of ‘infiltrating at source’. Further, the WSUD principle of detaining flood volumes near the source also extends the duration from which stormwater can be extracted from the drainage network. Another approach is to increase invert levels at appropriate locations in the drainage network to decrease groundwater exfiltration into the Main Drains. A concomitant increase in the channel width along these reaches is required to maintain hydraulic capacity for conveyance of floods. Both of these strategies aim to maintain water in the superficial aquifer rather than losses via the drainage network. Potential
locations for drainage water storage options (lined and unlined basins, below ground basins, groundwater) are summarised on the basis of spatial constraints (i.e. depth to groundwater, distance from Main Drain, soil type, acid sulphate soils, wetlands and Public Drinking Water Source Areas).
An integrated approach is suggested to realise the potential for stormwater harvesting of the drainage waters that includes:
*Continue implementation of the WSUD principle of ‘infiltrate at source’;
*Identification of suitable reaches along the Main (and Local) Drain network to raise invert levels and widen the channel;
*Extraction of winter and spring baseflows with injection (or infiltration) into the superficial aquifer; and
*Storage of stormwater events in detention basins with possible injection or infiltration into the superficial aquifer.
Urbanisation of catchments can generate substantial stormwater runoff. In the Perth metropolitan region an extensive drainage network collects and conveys stormwater runoff that is subsequently discharged to the Swan-Canning Estuary or ocean outlets. Similarly, the drainage network of the Peel region within the Metropolitan Region Scheme collects and conveys stormwater runoff that is then discharged into the Serpentine River and ultimately to the Peel-Harvey Estuary.
The Department of Water (DoW) is investigating the potential for stormwater harvesting from the drainage network within the Perth metropolitan and Peel regions as a source of potable or non-potable water. Understanding the potential use of this resource is important because of the uncertainty in future water sources and supply. Additionally, there is growing environmental awareness within the community and a changing view of stormwater from a waste product to a valuable resource (Department of Environment 2004).
The objective of this study is to estimate stormwater quantity in the Perth and Peel regions, to identify harvesting strategies and to provide a preliminary indication of geographical locations that may be suitable for surface or groundwater storage of this potential resource.
The study area is shown in Figure 1. There are approximately 830 km of Main Drains in the Perth Metropolitan region with more than 3000 km of Local Drains. The study area primarily focuses on regions serviced by Water Corporation Main Drains for several reasons, namely:
t Data availability: Long-term discharge data is available from the Main Drains but not the Local Drains;
t Numerical modelling: Discharge from the Main Drains into the Swan-Canning Estuary have been simulated over the period of 1965-2000 with a catchment hydrology model; and
t Greater Water Harvesting Potential: Greater discharge in the Main Drains results from the aggregation of stormwater runoff from the Local Drains.
Several areas in the study region not included in this analysis including:
t Northern coastal suburbs: Rainfall does not generate substantial stormwater runoff, rather much of the water infiltrates rapidly into the superficial aquifer;
t Rockingham Main Drains: Data was not available to estimate stormwater discharge of the Rockingham Main Drains; and
t Upper Swan River: The upper Swan River (Avon, Ellen Brook, Helena, Susanah Brook, Jane Brook) catchments were not assessed. However, the stormwater harvesting principles developed here are valid for these waterways as well.
The objectives of the Perth Urban Water Balance Study (Water Corporation 1987) were to:
t Identify areas where unconfined groundwater resources may be at risk;
t Investigate the areas greatest at risk; and
t Identify groundwater management options for risk areas.
A representative water balance model for the Perth urban area was developed. The water balance was developed by equating changes in groundwater storage from inputs and outputs. Inputs included rainfall, groundwater inflow and artificially imported water. Outputs included evapotranspiration, groundwater outflow, wastewater disposal and surface drainage.
This study identified that the drainage network can be either an input into groundwater via infiltration basins or an output via drainage networks. Stormwater runoff was estimated as rainfall over the percentage of impermeable areas that drain to the receiving environments. The potential for additional stormwater runoff to recharge groundwater through infiltration basins was suggested.
The Environmental Protection Authority (EPA) published Bulletin 1131 (EPA 2004) in response to a request for advice on statutory mechanisms to control the quality and quantity of drainage into the Swan and Canning rivers. Bulletin 1131 reviewed the outcomes and recommendations from a number of previous drainage management studies and the Drainage Management Forum of late 2003 to early 2004. Key recommendations from Bulletin 1131 include:
t Effective management of urban drainage was identified as a high priority to reduce nutrients to the Swan and Canning Rivers;
t Total water cycle management was outlined as a requirement in urban drainage management in order to improve water use efficiency through increasing the capture, storage and reuse of water close to the source;
t The review identified drainage management responsibilities within the metropolitan region. There are 29 local governments managing approximately 80% of the drainage network (the local drains), while the Water Corporation manages the remaining 20% (the Main Drains); and
t Stormwater drainage estimates in the Bulletin are over 200 GL of stormwater is conveyed to the rivers and ocean. However, the source or method of this volume estimate is not outlined.
To reiterate the objective of this investigation is to estimate the quantity of stormwater runoff and to identify suitable storage options of harvested stormwater for re-use. The approach was as follows:
t Estimation of the discharge volume through the drainage network and the seasonal pattern of the flows1;
t Review and development of suitable stormwater ‘harvesting’ options; and
t Identification of geographical areas to implement stormwater harvesting techniques.
Multiple sources of information were used to estimate stormwater runoff in the Perth and Peel regions. These included:
t Discharge data from gauging stations at several key locations were used to:
o Characterise seasonal baseflow patterns in the Main Drains;
o Validate numerical simulations of the Main Drain catchments that discharge into the Swan-Canning Estuary; and
o Develop linear regression relations between several Main Drains in the Peel region to synthesise a long term record for one of the drains;
t Prior simulations with LASCAM (LArge SCale CAtchment Model) served to estimate the stormwater volume of the Main Drains into the Swan-Canning Estuary; and
t Approximate annual estimates of three coastal Main Drains from the Water Corporation.
Options for stormwater storage were then developed. This included the identification of opportunities and constraints in the siting of these storage techniques. Spatial mapping was then used to identify suitable locations and their areal extent to implement storage options for stormwater harvesting.
Specifically, the study’s methodology included:
• Review of available discharge data from drainage monitoring stations;
• Comparison of selected Swan-Canning Main Drain data with LASCAM simulations;
• Estimation of total annual runoff of the Swan-Canning region Main Drains with LASCAM simulations;
• Estimation of total annual runoff of several of the Peel region Main Drains with available discharge data and statistical correlations;
• Forecast the impact of inter-annual climate variability on stormwater quantity;
• Examination of seasonal patterns of baseflow in the Main Drains;
• Review of stormwater harvesting options and implementation considerations;
• Spatial opportunities analysis of stormwater harvesting options; and
• Examination of potential locations and areal extents for each harvesting option.
1 This latter point is important in the selection of appropriate harvesting and storage options.
4. Data Analysis
In this investigation annual discharge was estimated for the Main Drains of the Swan-Canning Estuary and several within the Peel region. It was assumed that stormwater harvesting from Main Drains generally provides a more consistent source to design stormwater harvesting and storage infrastructure than the Local Drains.
This study did not consider flood discharge from the upper Swan River inclusive of the Avon River, Ellen Brook, Jane Brook and Susanah Brook. Annual discharge estimates are provided for these waterways, but the focus here was on the Main Drains of the Swan-Canning catchment and the Peel region.
Additionally, estimates of stormwater quantity for the northern urban corridor were not included in the analysis. Firstly, there is a lack of drainage discharge data for this region. Secondly, much of this region has natural high rates of infiltration negating the need for Main Drains to convey stormwater runoff or to manage water levels of the superficial aquifer.
Though stormwater quantity was estimated for several ‘focus’ regions, namely the Swan-Canning and Peel Main Drains, the subsequent spatial analyses to identify suitable stormwater storage options considered the entire area of the Metropolitan Region Scheme.
4.1 Gauging Station Data
Several of the waterways in the study area had discharge data of sufficient duration from either the Water Corporation or DoW to allow estimation of discharge (Table 1 and Figure 2). These gauged Main Drains were representative of different regions within the study area.
5. Options for Stormwater Harvesting
This section considers major options for storage of runoff from the Swan-Canning and Peel Main Drains. The stormwater harvesting options are also applicable to Local Drains. The Stormwater Management Manual for Western Australia (Department of Environment 2004) states that the aging drainage systems within established urban areas provide an opportunity for retrofitting to increase stormwater infiltration and reuse.
Here a number of retrofitting options are considered to increase reuse of stormwater within urban areas inclusive of:
t Water Sensitive Urban Design (WSUD);
t Managed Aquifer Recharge (MAR), which in this report is narrowly defined as extraction of water from the Main Drains (via pumping) and recharging the superficial aquifer a sufficient distance from any Main or Local Drains;
t Underground Storage Systems to store Main Drain runoff either from winter/spring baseflow or from episodic stormwater events;
t Above Ground Storage Systems to be used in a similar manner as the Underground Storage Systems; and
t Drainage Channel Modification whereby the invert levels (i.e. base levels) of the Main Drains are elevated to drain less of the local groundwater stores and widened to maintain hydraulic capacity.
Next, further brief descriptions are given for each of the harvesting options along with identification of opportunities and constraints in their application.
5.1 Stormwater Aspects of Water Sensitive Urban Design (WSUD)
Among other objectives water sensitive urban design (WSUD) aims when possible to infiltrate locally generated stormwater ‘at source’. Examples of WSUD methods include infiltration basins and swales, as well as lot scale infiltration via soakwells, are all now widely encouraged and used within urban areas.
These methods follow the WSUD principles outlined in the Stormwater Management Manual for Western Australia (Department of Environment 2004).
Another objective of WSUD is to attenuate stormwater peaks in the drainage network. In Perth new urban developments must be able to store the 1 annual recurrence interval (ARI) discharge on site. In effect this attenuates stormwater peaks over a longer period of time.
5.1.1 Opportunities and Constraints
Clearly both of these WSUD objectives (stormwater infiltration at source and flood attenuation) provide opportunities for greater stormwater reuse. The first objective of stormwater infiltration at source is a direct manner to decrease the loss of this resource via the drainage network and to the estuary or ocean. The second objective of attenuating the flood peak in the drainage network provides two opportunities:
t Decreases the magnitude of floods thereby decreasing the size of infrastructure to harvest the resource; and
t Through storage of the 1 year ARI flood on site with release over approximately a 36-72 hours, the time to harvest the ‘peak episodic events’ of this resource is extended relative to the current case. re is greater duration to period.
Implementation of WSUD principles clearly is limited by geology and underlying soils. In sandy environments high infiltration rates provide a favourable setting for rapid dispersion of stormwater runoff into the groundwater stores. On the other hand, clay soils do not. Rather in these environment the second aim of WSUD considered for the purposes of this investigation (flood attenuation via storage of 1 year ARI flood on site) allows more stormwater to be harvested on site or downstream through extending the detention period.
5.2 Groundwater Storage
The groundwater storage option is a reuse strategy whereby stormwater is extracted and injected (via wells or infiltration basins) into suitable aquifers (likely the superficial) for later use in times of peak demand. In this approach the aquifer is treated as a storage facility similar to surface water storages such as basins. Stormwater recovery would include single or multiple recharge well to the superficial aquifer within the metropolitan area. In this investigation the groundwater storage option is limited to a
non-potable water supply because recharge to the confined aquifers (i.e. Leederville) as treatment would likely be required beforehand.
5.2.1 Opportunities and Constraints
The stormwater quality is a primary constraint. Although biogeochemical processes within the soil or groundwater may improve water quality, contaminants may not be removed (or immobilised) sufficiently thereby yielding unacceptable risks to aquifer contamination (Department of Environment 2004). First autumn flush events have been identified as a major stormwater pollutant source. However, elevated nutrient and metal concentrations also occur during subsequent stormwater events after the first flush and therefore pre-treatment of runoff may be required throughout the year (Department of Water 2007). Pre-treatment of stormwater may also be required prior to injection or infiltration into the groundwater stores to prevent clogging of the substrate.
Spatially the stormwater must be conveyed sufficient distance from Main (and deep Local) Drains so that the injected stormwater is not rapidly discharged via the groundwater pathway back to the drainage network. Technically this spatial constraint will require pipes to transport water from the Main Drains to the injection location.
Further, input into groundwater stores via large infiltration basins requires substantial land to be effective. In cases where these facilities need to be retrofitted within established urban areas, land reclamation may be required. While surface storage facilities typically comprise only a small part (2-3%) of the contribution catchment (Department of Environment 2004), land is typically scarce or prohibitively expensive in many parts of the metropolitan region. Where land constraints disallow large scale infiltration basins, groundwater storage may be achieved through storage and pre-treatment of water within surface or below ground storage facilities, which is then followed by injection into the superficial aquifer.
Suitable attributes of the superficial aquifer to implement this groundwater storage option within the metropolitan region include soil type and permeability, and sufficient depth to groundwater table.
Typically infiltration or injection of water into the superficial aquifer will require a soil with moderate to
high permeability. In addition soils that feature an aquitard or bedrock at shallow depth will be unsuitable. Acid sulphate soils (ASS) are also a consideration as this groundwater storage option may lead to large variation in groundwater level and the generation of acidity.
5.3 Underground Storage Systems
Underground Storage Systems capture and store runoff in large pipes and/or other subsurface structures. This stored water may be released to the environment through an outlet pipe or allowed to infiltrate to recharge groundwater. Subsurface storage systems may be constructed from concrete, rigid plastic (HDPE), steel or aluminium. Benefits associated with underground stormwater retention/detention have been identified as including:
t Attenuation of peak stormwater flows;
t Potential for extended storage and slow controlled release of collected stormwater runoff;
t Prefabricated modular systems that can be rapidly installed and require limited land, therefore suitable for high density or expensive urban areas;
t Materials are durable and have extended life spans (50+ years); and
t Underground storage improves public safety and may be more aesthetically pleasing than some surface storage options.
5.3.1 Opportunities and Constraints
Similar to MAR the major constraints to underground storage is stormwater quality as inadequate pre- treatment may lead to contamination of superficial groundwater. If harvested stormwater is to be infiltrated into groundwater then pre-treatment of runoff should incorporate Best Management Practices in-line with the storage system (i.e. a treatment train approach). Alternatively, the harvested stormwater could be simply stored for later non-potable reuse.
Underground storage systems are typically not constrained by available land though extensive excavation during the installation phase may be required. Though soil types do not constrain the location of underground storage facilities, during construction prevention of exposure or mobilisation of ASS needs to be implemented to avoid further water quality issues.
The largest constraint to underground storage systems is cost. A ‘rule of thumb’ cost for underground storage in large diameter pipes is $1,000 per cubic metre.
5.4 Above Ground Storage
In this investigation Above Ground Storage of stormwater is storage within an above ground facility that enables abstraction at a later date. A number of storage options are included within this category such as stormwater re-use ponds, detention basins and constructed wetlands. Wetlands as mapped under the Geomorphic Data Atlas are not incorporated within this category as abstraction of water from these wetlands is prohibited. Further, permanently inundated basins of open water formed by simple dam walls or by excavation below ground level must comply with DoW’s July 2007 ‘Interim Position Statement: Constructed Lakes’.
5.4.1 Opportunities and Constraints
Each of these Above Ground Storage systems can store urban drainage runoff and generally improve water quality. Stormwater reuse ponds and detention basins generally are deeper than constructed wetlands, and if are lined then do not have any soil constraints in their siting. Constructed wetlands are generally unlined with connections to the groundwater table that also provide habitat for flora and fauna.
Above ground storage can be problematic because of high evaporative and seepage losses for unlined basins during summer months. Land requirements for off-stream (or off-drain) above ground storages may also be prohibitively expensive and spatially unavailable. In-stream (or in-drain) above ground storages need to be carefully designed to maintain hydraulic capacity for flood events.
5.5 Modification of Main Drain Channel Morphology
Historically, the Main Drains (and Local Drains) were designed for two primarily two purposes:
t Stormwater drainage systems to alleviate flooding; and
t Lowering superficial aquifer levels through interception, collection and conveyance for a number of historical reasons (i.e. improve agriculture, lower levels for septic tanks).
These historical drivers either no longer exist (i.e. centralised wastewater treatment) or are being managed with new approaches (management of stormwater via WSUD).
Hence, one manner to increase stormwater reuse3 is to modify the morphology of the Main (and Local) Drains to reduce winter groundwater losses and yet maintain the flood hydraulic capacity. This can be achieved by elevating the inverts of the Main Drains so that less of the upper superficial groundwater level is intersected thereby decreasing losses from the subsurface stores. Concomitantly the channel width would be increased to accommodate the required (or design) flood discharge conveyance. In short, through modification of the Main (and Local) Drain channel morphology from a deep incised channel to a wide shallow channel, much less groundwater will be lost across the Swan-Canning and Peel regions (particularly in the sandy geological regions).
5.5.1 Opportunities and Constraints
Most of the opportunities and constraints with this approach revolve around spatial considerations. Implementation of this approach would only be able to occur in regions where there is sufficiently wide reserve to widen the Drain sufficiently to meet stormwater hydraulic capacity needs as required given the amount the invert level is raised. There also needs to be sufficient room to allow access for maintenance activities of the Main Drain. In light of these spatial considerations, it is likely that there are some reaches where channel modification to the morphology could be implemented in the short term.
3 Better stated as a manner to reduce losses of groundwater derived from stormwater infiltration.
6. Spatial Analysis
As outlined in Section 5 the stormwater harvesting options evaluated within this report have a number of environmental attributes that determine the viability of each option. Spatial data sets that represent these environmental attributes were collated for the study area and are briefly described below. For the groundwater storage options it has been assumed that later abstraction of injected, infiltrated or stored groundwater from over allocated Ground Water Source Areas (GWSAs) will not be an issue.
6.1 Overview of Spatial Attributes
The Environmental and Urban Geology Map Series 1:50,000 for the Perth Metropolitan Region (Geological Survey of Western Australia) was used to represent the soil types for the study area (Figure 10). Using the broader geological units, the soil types were simplified and ranked according to their suitability for the different stormwater storage methods that were evaluated.
6.1.2 Depth to Groundwater and Water Corporation Drainage
While there is extensive data for groundwater table depth in m AHD for the Perth Metropolitan Region, there is no existing spatial dataset of depth to groundwater relative to the surface. Davidson (1995) included broad scale mapping of the depth to groundwater below ground level for the Swan Coastal Plain. The map by Davidson (1995) was generated from groundwater depths from September and October 1992. Some spatial inaccuracies are likely in Davidson’s (1995) depth to groundwater image because of scale and density of bores from which the image was derived. Nonetheless, the map is useful as it represents a conservative estimate of groundwater levels for the study area during a wetter period with greater superficial groundwater stores than currently. The map was digitised to enable consideration in the spatial analysis of this investigation (Figure 11). The depth to groundwater is an important spatial consideration for nearly all of the stormwater reuse options considered here.
Further, on the same image the Water Corporation Main Drains are illustrated (Figure 11). This spatial data set is particularly important in determining appropriate regions in which to infiltrate or inject stormwater via MAR. This was implemented by creating spatial buffers around the Main Drains based on the distance from Main Drains in which harvested stormwater that is stored in the groundwater would not return to the drainage network for a reasonable duration (i.e. at least 1 year).
6.1.3 Acid Sulphate Soil Risk
The Western Australian Planning Commission (WAPC) Planning Bulletin No 64 outlines Acid Sulphate Soil (ASS) risk areas within the study area (Figure 12). The dataset was collated at the 1:50,000 scale for broad scale assessment of ASS risk associated with the stormwater reuse options.
6.1.4 Geomorphic Wetlands and Public Drinking Water Source Area
The DoW’s Geomorphic Wetlands dataset (Department of Water) comprises wetlands of the Swan Coastal Plain that have been classified as either Conservation, Resource Enhancement or Multiple Use
6.2 Definition of Spatial Opportunities for Stormwater Storage
Table 2 below presents the ideal input parameters, or opportunities, for three of the stormwater harvesting options, namely MAR, Above Ground Storage and Below Ground Storage. WSUD can be implemented throughout the catchment and modifications to the morphology of drainage channels are obviously spatially constrained to the locations of Main and Local Drains.
Shaded input parameters in Table 2 are mandatory constraints. Where input parameters are not shaded, the ideal input parameter is shown, but other parameter values or types may be viable.
During the formulation and definition of the appropriate criteria to delineate regions across the study area for the various stormwater harvesting options, it became evident that MAR substantially differed from both Above and Below Ground Storage options. In particular, MAR requires a underlying geology type that rapidly infiltrates to the superficial (sands and limestone) and regions that are a substantial distance from Main Drains (>500 m).
It became apparent that the spatial criteria for ‘lined’ and ‘unlined’ Above Ground Storage options were the same except for underlying geology. ‘Unlined’ Above Ground Storage could only occur in regions with clays, otherwise the water would be returned immediately again to the drain as these options would be placed close (<250 m) or within the drain. Further, the ‘lined’ Above Ground Storage option was the same as the Underground Storage Option (i.e. void) whereby these structure could be placed in any underlying geology within close proximity to the Main Drain (<250 m).
Table 2 Spatial opportunities matrix for stormwater storage options
Above Ground Storage Unlined
Below Ground Storage and Above Ground Storage Lined
Sands and limestone
Depth to Groundwater
Distance from existing drainage line
Acid Sulphate Soil
Low (and Moderate)
Low (and Moderate)
Low (and Moderate)
Geomorphic Wetlands >50 m from CC4
>30 m from RE5
>50 m from CC
>30 m from RE
>50 m from CC
>30 m from RE
4 Conservation category
5 Resource enhancement
6.3 Locations of Stormwater Storage Options
Next a series of locations over the study area that spatially represent suitable locations for three of the stormwater storage options (groundwater storage, Above Ground Storage, Below Ground Storage) are presented. The basis for the siting of the three stormwater options was based on the spatial opportunities defined in Table 2. Initially, only low ASS potential was evaluated as suitable sites for any of these options because of either enhanced groundwater level fluctuations and acid mobilisation via MAR, or alternatively construction impacts via the above or below ground storage options. However, because management and operational strategies are available to mitigate for these related issues in moderate risk soils for ASS, spatial representations are also illustrated in these regions.
6.3.1 Groundwater Storage Option
The most suitable sites for the implementation of groundwater as a stormwater storage option are mainly along the corridor of sandy soils within 5-10 km of the coast (Figure 14). The primary constraints along
this area are regions of extensive wetlands. The total area available for the implementation of MAR is approximately 864 km2 (Table 3).
6.3.2 Underground Voids and Lined Surface Basins
Because of the requirement that Below Ground Storage and Above Ground Storage options are in close proximity to the Main Drains, the areal extent was considerably less than the MAR option. An areal extent of approximately 275 km2 would be suitable to place either underground voids or lined surface basins for the storage of stormwater (Table 3). These areas are concentrated in regions where the Main
Drain network occurs around the perimeter of the Swan-Canning Estuary and the eastern Peel region (Figure 15). Clearly, some portion of the Local Drains would also be suitable for these types of storage options, but the focus of this initial investigation into the potential for stormwater reuse was on the Main Drains.
6.3.3 Unlined Surface Basins
For ‘unlined’ surface basins again the requirement that Above Ground Storage option is in close proximity to the Main Drains and in appropriate underlying geology (i.e. clay soils), the areal extent was
considerably less than the underground void and line surface basin options. An areal extent of approximately 70 km2 would be suitable to place unlined surface basins for the storage of stormwater (Table 3). These areas are concentrated in the proximity of the Main Drain network of the eastern Peel region (Figure 16). Clearly, some portion of the Local Drains would also be suitable for these types of
storage options, particularly in the eastern Peel region, but the focus of this initial investigation was the potential for stormwater reuse of the Main Drains.
category wetlands (Figure 13). The wetland category, based on a series of geomorphic characteristics, provides guidance on the level of wetland protection that wetlands are afforded.
Public Drinking Water Source Area’s (PDWSA’s) are defined areas in which restrictions are placed on activities that may pollute surface or groundwater sources. The DoW’s PDWSA dataset shows that within the study area boundary three gazetted PDWSA occur (Figure 13). These correspond with the Gnangara and Jandakot water mounds, and the Dirk Brook Water Reserve corresponding with the proposed Karnup-Dandalup PDWSA.
This evaluation indicates a significant volume of stormwater is generated in the Perth Metropolitan and Peel regions that can be harvested as a non-potable water supply. Patterns of baseflow two typical Main Drains (Bayswater and Yule Brook) illustrate that winter baseflow provides a constant source of stormwater runoff. This baseflow can be pumped directly from the Main Drain and infiltrated or injected into the superficial aquifer as a storage option. Stormwater harvesting into basins and voids is recommended to capture and to store runoff from episodic storm events. Temporary storage of episodic stormwater volumes in these above or below ground storage basins can also serve as a supply source for subsequent injection or infiltration into the aquifer.
Current recommended practices of ‘stormwater infiltration at source’ decreases stormwater ‘losses’ down the drainage network and storage in the aquifer. Further, if the surface geology is not appropriate for infiltration, then detention and ‘slow release’ of stormwater into the drainage network provides additional ‘time’ for the stormwater to be appropriately extracted from the Main Drain.
Lastly, opportunities throughout the network of Main and Local Drains to modify the cross-sectional morphology to decrease groundwater losses (increase invert level), but yet maintain flood conveyance capacity (widen the channel) need to be identified and assessed.
This analysis represents an initial broad scale assessment of the potential for stormwater harvesting via pumping into aquifers, and storage in basins and voids. Clearly, further work is required at the local scale to assess the viability of these three stormwater harvesting options at any particular site. Local studies should assess aquifer characteristics in order to determine storage requirements. At the more detailed site assessment stage further considerations include the impact of contaminated sites on siting of both above and below ground storage methods.
Nonetheless some general approaches have emerged as integrated strategies to harvest stormwater that include:
t In suitable areas with laterally wide drainage reserve modify the Main (and Local) Drain morphology to drain less groundwater;
t Target winter and spring seasonal base flows in the Main Drains for removal via pumping and injection into aquifers. This does not require large basins to hold or retain the water. Pumps can be placed in small off-drain basins or within the drains to extract water, which can then be transported a sufficient distance to recharge the superficial aquifer; and
t Utilise Below or Above Ground Storage Basins to capture and retain stormwater events. Storage of this water is recommended throughout the winter and spring, but then can utilise the same groundwater pumps to inject into groundwater during the summer and autumn when the Main Drain baseflow is lower.
Lastly, this study only considered the quantity and not quality of stormwater discharge. It is recommended that an investigation to characterise the stormwater quality be undertaken. Further, consideration of this stormwater resource as a potable water supply will require investigations into treatment needed during and prior to distribution.
Davidson, W.A. (1995) Hydrogeology and groundwater resources of the Perth Region, Western Australia. Geological Survey of Western Australia, Bulletin 142.
Department of Environment (2004) Stormwater Management Manual for Western Australia. Department of Environment, Perth, Western Australia.
Department of Water (2007) Contaminants in Stormwater Discharge, and Associated Sediments, at Perth’s Marine Beaches; Beach Health Program 2004-2006. Department of Water, Perth, Western Australia.
Environmental Protection Authority (2004) Drainage Management, Swan-Canning Catchment, Bulletin 1131. Environmental Protection Authority, Perth, Western Australia.
Water Corporation (1987) Perth Urban Water Balance Study, Water Authority of Western Australia, Perth.
Zammit et al. (2002) An integrated ecological model of catchment hydrology and water quality for the Swan-Canning Estuary: Volume 2. Final report to the Western Australian Estuarine Research Foundation.
Report for Potential Use of Stormwater in the Perth Region
Quantity and Storage Assessment
Prepared for the Department of Water
Rainwater Harvesting Petition—Have You Signed?
I know many of you have already seen—and perhaps signed—the rainwater harvesting petition that’s been widely circulating, but for those who might not be aware of it, I want to call attention to it once more before next week’s deadline.
The American Rainwater Catchment Systems Association launched a petition last month to encourage rainwater harvesting. ARCSA is hoping to collect 100,000 signatures by December 16.
In times of drought it’s easier to convince the public that rainwater harvesting is a good idea. This article includes some interesting statistics about how recent storms in the Los Angeles area have replenished the aquifer, but the ARCSA’s goal is to stimulate an industry to more actively capture rainwater—and to create jobs in the process.
The full text of the petition appears below. You can find and sign the petition by clicking on this link: http://wh.gov/ia5tT.
We petition President Obama to stimulate the emerging rainwater-harvesting industry through legislation or executive order, creating new jobs in design, installation, education, R&D, sales, plumbing, landscaping, roofing, monitoring and maintenance, which could propel the U.S. to international leadership, with compounding fiscal benefits.
The many justifications include:
- Worldwide demand for clean water exceeds supply.
- Rainwater can help fill the gap and reduce stormwater pollution.
- One inch of rain is over 600 gallons per 1,000 sq. ft. of roof.
- Rainwater is a valuable resource that reduces demand on water infrastructure.
- A new national standard, ARCSA/ASPE/ANSI 63-2013 details safe design & installation.
- Treated rainwater can easily surpass EPA standards.
By: Kaspersen, Janice: Stormwater Editor
An update in response to the comment below: For anyone interested in the complete text of the new standard, it is available for purchase from ASPE’s website at
For those who have inquired, the ARCSA/ASPE/ANSI Standard 63 reference is included in the petition to inform anyone who might have doubts that rainwater could be harvested and treated to high standards. It was originally known as a “design and installation” standard and can still be thought of as such, having survived the rigorous technical and public scrutiny requirements to become an ANSI standard. It is copyrighted and sold by the author agencies.
The 46-page document would be difficult to condense for inclusion in this blog, but the Table of Contents includes:
2.0 Referenced Standards
4.0 Design and Installation Requirements, which includes Collection Parameters, Conveyance System, Pre-Filtration, Cisterns/Storage, Pump, Filtration, Piping, System Inspection and Maintenance, Potable Water Applications, Operation and Water Quality Maintenance and Labeling.
Appendix A Additional Relevant Standards
Appendix B Example of Piping Schematic
Appendix C Reference Definition
Appendix D Example Maintenance
Appendix E Calculation Procedure
Appendix F Average Rainfall Data