identification of water sensitive urban design measures ... · identification of wsud measures and...

Important Notice This report applies only to the subject of the project. University does not accept responsibility for the conformity or non-conformity of any other subject to the findings of this report. This report consists of one cover page and 22 pages of text. It may be reproduced only with permission of the copyright owner, and only in full.

Educating Professionals Applying Knowledge Serving the Community

Identification of Water Sensitive Urban Design Measures and Approaches for Sustainable Stormwater Management

Report – Part C Harvesting, Re-Use and Flood Mitigation (minor events)

Prepared for Catchment Management Subsidy Scheme, Transport SA, Adelaide & Mount Lofty Ranges Natural Resources Management Board, Local Government Association and Environment Protection Authority

Prepared by Urban Water Resources Centre University contact David Pezzaniti Group Leader Telephone +61 8 8302.3652 Facsimile +61 8 8302.3386 Date of issue December, 2006

ISO 9001 QEC6382

Educating Professionals • Creating and Applying Knowledge • Serving the Community

Division of IT, Engineering and the Environment

Identification of WSUD Measures and Approaches Report – Part C

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TABLE OF CONTENTS

1 HARVESTING AND REUSE................................................................................ 1

1.1 RAINWATER TANKS ........................................................................................... 1 1.1.1 Individual Rainwater Tanks ................................................................................................. 1 1.1.2 Catchment Wide Rainwater Tanks Combined Benefit ......................................................... 2

1.2 AQUIFER STORAGE AND RECOVERY .................................................................. 3 1.2.1 Allotment Level ASR ............................................................................................................ 3 1.2.2 Catchment Level ASR........................................................................................................... 4

1.3 ALLOTMENT VS CATCHMENT LEVEL HARVESTING............................................ 6 1.4 RE-USE COMBINED WITH FLOOD MITIGATION .................................................. 7

2 FLOOD MITIGATION (MINOR EVENTS)....................................................... 8

2.1 CATCHMENT MODEL ......................................................................................... 8 2.2 MODEL CALIBRATION........................................................................................ 9 2.3 INITIAL MODELLING ........................................................................................ 11 2.4 MODELLING METHODOLOGY........................................................................... 12 2.5 DISTRIBUTED INFILTRATION/FILTRATION DEVICES ......................................... 13 2.6 CATCHMENT SCALE INFILTRATION BASINS ..................................................... 15 2.7 CATCHMENT ASR SCHEMES (SIZED FOR LOCAL DEMAND)............................. 16

3 CONCLUSIONS AND RECOMMENDATIONS.............................................. 18

3.1 HARVESTING AND RE-USE ............................................................................... 18 3.2 FLOODING(MINOR EVENTS).............................................................................. 18

REFERENCES.............................................................................................................. 20

FIGURES

Figure 1-1 Annual Yield and Cost per kL for a 1 kL Tank Figure 1-2 Annual Yield and Cost per kL for a 2 kL Tank Figure 1-3 Rainwater Tanks Combined Yield and Costs Figure 1-4 Allotment Level ASR Combined Yield Figure 1-5 Location of potential ASR sites Figure 1-6 Unit Production Costs of Harvested Stormwater Figure 2-1 EPA SWMM Model for Meakin Tce Catchment Figure 2-2 Flow Monitoring


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Figure 2-3 Outflow from Catchment during July 1 Event (13:30 pm) Figure 2-4 Model Results - February 21, 1977 Figure 2-5 Typical Operating Ranges for Devices Compared with Modelled Limits Figure 2-6 Reduction in Flooding Volume vs Return Period - Crittenden Rd Figure 2-7 Reduction in Flooding Volume vs Return Period - Tapleys Hill Rd/Meakin

Tce Figure 2-8 Reduction in Flooding Volume vs Return Period

TABLES

Table 1-1 Plumbed In-House Rainwater Tank Costs Table 1-2 Summary of ASR Schemes Table 2-1 Modelled vs Measured Flow Data at Catchment Outlet – July 1, 2006 Table 2-2 Number of Infiltration Basins Required for Varying Areas of Catchment

Treated


Urban Water Resources Centre, University of South Australia Page 1 of 20

1 HARVESTING AND REUSE Harvesting and reuse strategies at the allotment to catchment level were investigated and then compared for yield and cost. Options assessed were allotment level rainwater tanks and catchment scale aquifer storage and recovery (ASR) schemes. Only ASR schemes at the catchment scale were considered practical as other harvesting/storage methods such as underground tanks, open storages etc were considered cost prohibitive. These are described in more detail in the following sections.

1.1 Rainwater Tanks

1.1.1 Individual Rainwater Tanks As of July 2006 all new residential dwellings must have a minimum of 50 m2 of roof area connected to a 1,000 litre rainwater tank for in-house use (minimum toilet and/or laundry). The current total number of dwellings in the catchment is estimated at 4,185 with a potential increase in the number of dwellings due to re-development of approximately 950 (Tonkin, 2003). Based on continuous modelling of daily rainfall for Adelaide, using a recently developed raintank analyzer (Argue et al, 2004) available at www.newdev.unisa.edu.au/water/UWRG/publication/raintankBETAv1.xls the annual yield for a 1 kL and 2 kL rainwater tanks for connected roof areas of 50 to 100 m2 are indicated in Figures 1.1 and 1.2. These curves also indicate the cost per kilolitre of water delivery using the loan repayment method, taking into account initial capital costs, pumping, maintenance and replacement costs. Costs have been obtained from the raintank centre (see Table 1.1).

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Figure 1-1 Annual Yield and Cost per kL for a 1 kL Tank



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Figure 1-2 Annual Yield and Cost per kL for a 2 kL Tank

Table 1-1 Plumbed In-House Rainwater Tank Costs

Tank Size

L

Supply (Delivered)

Pipework and Labour

Plumbing to House

Support Structure

Pump and mains water backup

controller

500 300 200 400 40 750

1,000 400 250 400 60 750

2,000 600 300 400 200 750

5,000 650 350 400 300 900

10,000 1,000 400 400 400 1,100

20,000 1,800 450 400 600 1,100

1.1.2 Catchment Wide Rainwater Tanks Combined Benefit Figure 1.3 presents a summary of the combined annual yield and annualised costs associated with progressively installing rainwater tanks in the catchment for new dwellings. These costs include initial capital costs and on-going costs such maintenance, pumping and replacement costs. Note that for an increase in the number of dwellings of 950, the total number of dwellings available for including raintanks as part of the re-development is considered to be approximately 1,500. This takes into account redevelopment where an existing allotment is subdivided and either one or two new dwellings are built.



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Combined annualised costs for 1 kL tanks

Combined annualised costs for 2 kL tanks

Combined annual yield for 1 kL tanks

Combined annual yield for 2 kL tanks

Assumptions:1. connected roof area of 100 m22. daily demand 100 litres3. Maximum number of new dwellings = 1,5004. Annualised cost based on loan repayment method

Figure 1-3 Rainwater Tanks Combined Yield and Costs

1.2 Aquifer Storage and Recovery

1.2.1 Allotment Level ASR It may be possible to consider injecting filtered roof water into a shallow bore for new dwellings for irrigation reuse (and possibly in-house toilet flushing). As new allotments typically have reduced lawn areas (typically 100 m2), it is possible to meet the annual irrigation requirements typically required for lawn areas (typically 500 mm/m2 per year) from water harvested from the roof. This could potentially reduce domestic water use by approximately 50 kL per year for each new dwelling. Alternatively, runoff water may be directed to landscaped storage areas (eg raingardens) where infiltration can occur. Re-use can be achieved with the use of a shallow bore, if required. Such schemes could eliminate the need for on-site rainwater tanks, and where surface storage is available can enable allotment outflows for critical minor storm events to be retained on-site. Figure 1.4 indicates the combined annual yield associated with progressively installing allotment level ASR in the catchment for new dwellings.



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Assumptions:1. yield based on irrigation requirements for 100 m2 lawn area2. Maximum number of new dwellings = 1,500

Figure 1-4 Allotment Level ASR Combined Yield

1.2.2 Catchment Level ASR Opportunistic catchment level re-use schemes are mainly located at the major reserves in the catchment where aquifer storage and recovery could potentially be incorporated. Injected water would most be suited to non-potable re-use such as irrigation of park reserves. Sites which appear to be suitable for such schemes within the catchment include:

1. Powerhouse reserve 2. Ledger oval 3. Matheson reserve/Findon High 4. Gleneagles reserve 5. Royal Adelaide golf course (RAGC)

Figure 1.5 indicates the location of each site.



Figure 1-5 Location of potential ASR sites

Injected water for ASR would require pre-treatment. For the purposes of sizing holding storages it was considered that a 3 day minimum retention time would be sufficient to achieve a suitable level of treatment prior to injection. An integrated wetland/storage arrangement was modeled at each site (refer to Report B – Water Quality for water quality improvements associated with ASR wetlands). Table 1.2 presents a summary of the details of each potential scheme.

Table 1-2 Summary of ASR Schemes

Site Existing open space area (ha)

Connected impervious area (ha)

Irrigation demand (ML/yr)

Min. holding storage

required (kL)

Harvested volume (ML/yr)

% of total runoff

harvested

Powerhouse 4.0 12.5 20 500 25 38.9

Ledger 1.9 23.3 9.5 195 12 10.0

Matheson 4.8 68.5 24 475 30 8.5

Gleneagles 4.0 21.7 20 445 25 22.3

RAGC 68.0 117 150 5,075 150 27.7 Notes:

1. maximum aquifer injection rate = 10 l/s (tertiary aquifer) 2. minimum retention time = 72 hours 3. maximum re-use = 80 % of injected water 4. irrigation rate = 500 mm/yr for open space areas (except Royal Adelaide golf course where estimated

irrigation rates are used) 5. each scheme is considered independently

Unit production costs for ASR schemes of varying sizes are indicated in Figure 1.4 (KBR, 2004). These costs have been derived from a range of ASR schemes that have been constructed mainly around Adelaide and include operational and maintenance costs as well as loan repayments. Land purchase costs have not been included as these will vary depending on the specifics of each scheme.

Powerhouse reserve

Ledger oval Matheson reserve

Gleneagles reserve

RAGC



Figure 1-6 Unit Production Costs of Harvested Stormwater

Based on the above the cost per kilolitre of water harvested using ASR techniques will range from approximately $1/kL (Royal Adelaide golf course scheme) to approximately $2/kL (Ledger oval scheme). Although the costs for the smaller scale schemes are higher than current SA Water charges for mains water use ($1.03/kL) these costs are substantially lower than the cost associated with rainwater harvesting at an allotment level, which for typical conditions is expected to be $9 to $9.50 per kilolitre (see Section 1.1).

1.3 Allotment vs Catchment Level Harvesting Catchment level harvesting using ASR schemes offer significant financial ($/kL) advantages compared to the combined effect of allotment level harvesting, particularly for schemes harvesting volumes in excess of 1ML/year. When reviewing the total long term combined potential harvested volume for 1 kL rainwater tanks on redeveloped allotments, the maximum amount of water that could be harvested throughout the catchment at the ultimate state of development is approximately 34 ML/yr. This represents a net reduction in mains water demand to the entire catchment in the ultimate state of development of approximately 3 %. The combined tank storage throughout the catchment is approximately 1,500 kL. The total combined annualised cost to the residents with 1 kL tanks is estimated at $325,000, although savings of approximately $34,000 are achieved through reduced mains water usage. This results in a combined net annualised cost of $367,000. An equivalent ASR scheme that harvests 34 ML/yr would cost the community approximately $59,500 per year (at $1.75/kL, refer to Figure 1.4). There may not necessarily be savings associated with mains water reductions for ASR schemes as water used for open space irrigation within the catchment may currently be derived from bore water. However,



an ASR scheme will enable sustainable long term use of groundwater and offers additional benefits to the community such as water quality improvements and potential social amenity values. ASR can also provide additional groundwater for other uses. This may also offer potential retail opportunities of harvested water. ASR schemes presented in this section have been sized to meet the local water requirements for open space irrigation. Each scheme is located at the area requiring irrigation. It may be possible to consider a single large scheme, such as the Royal Adelaide golf course ASR, rather than several smaller schemes. It may be possible for a large scheme to harvest enough water to meet the equivalent total catchment demand on groundwater. That is water injected at RAGC can offset borewater extracted at any of the reserves in the catchment. There may also be the opportunity to utilize additional groundwater credit to reduce mains water open space irrigation. This would particularly be applicable for reserves that are not adjacent to the main drainage network, where diversion of catchment runoff may be difficult. Examples of such schemes occur in the Salisbury City Council area. Issues such as cost sharing would need to be considered. Although medium to large scale harvesting schemes (when available) offer advantages over allotment level rainwater tanks, allotment level schemes should not necessarily be discouraged as this promotes the culture of re-use. Larger scale schemes will typically not provide direct reticulation re-use opportunities to individual households and as such allotment level rainwater tank harvesting is still valid for Water Proofing Adelaide. When comparing the combined effects of allotment vs catchment level harvesting schemes it is important to note the cost of allotment level schemes will be borne by individual residents, whereas larger scale schemes will be funded by the broader community.

1.4 Re-Use Combined with Flood Mitigation In some instances there may be the opportunity to combine harvesting/re-use schemes with immanent flood mitigation works. For example an ASR scheme can be incorporated into a flood mitigation basin that may be required within the catchment (eg Gleneagles basin). UWRC has recently concluded a trial on water quality improvements for a stormwater mitigation scheme at the Westwood development. This consisted of a 4 ha residential development that discharged to a flood mitigation basin. Water entering the basin was cleansed through the basin swale and subsurface gravel trench prior to discharging to the underlying aquifer. Water quality monitoring at the inlet and outlet of the basin and at the point of recharge and 10 m downstream of this point indicated that the scheme would meet EPA water quality requirements for irrigation re-use 3 days following a storm event. Section 2.7 reviews flood mitigation benefits associated with ASR wetland schemes considered in the catchment.



2 FLOOD MITIGATION (Minor events) In order to investigate the impact on flooding from implementation of WSUD, a catchment model using EPA SWMM (USEPA, 2005) has been developed. EPA SWMM is an integrated hydrologic, hydraulic and solute transport software package that can be used to model rainfall/runoff and drainage hydraulics, respectively. This model allows the performance of the underground pipe system to be modelled over a continuous time period. This can not be undertaken using the water quality model developed for the catchment using MUSIC. Continuous modelling was preferred to an event based model such as DRAINS, in order to allow antecedent conditions in storage devices to be modelled. WSUD measures previously selected for water quality and re-use assessment have been included in the model to determine the impact on minor system flooding. A further investigation into sizing devices to specifically address flooding issues has not been undertaken.

2.1 Catchment Model The development of the EPA SWMM model for the Meakin Tce catchment requires information related to sub-catchment characteristics such as areas, fraction impervious, depression losses, infiltration losses, pipe size and gradient and rainfall. A total of 51 sub-catchments were modelled, each discharging to a junction point connected to the main drainage line. The sub-catchments developed in the water quality modelling using MUSIC (refer to Report B – Water Quality) were replicated in the EPA SWMM model. Important modeling assumptions chosen include:

• Impervious depression storage = 1 mm • Pervious depression storage = 25 mm • Infiltration capacity = 36 mm/hr • Typical pipe slope = 0.2% • Catchment percent impervious as per values presented in Tonkin (2003) • Rainfall data based on 6 minute rainfall for Kent Town 1977-2002

To replicate localized flooding exhibited in the catchment, the model allowed for localized ponding at junction nodes during times of surcharge. This excess volume re-enters the network as capacity becomes available. Figure 2.1 presents the model developed for the catchment.



Figure 2-1 EPA SWMM Model for Meakin Tce Catchment

2.2 Model Calibration Historic flow monitoring is not available for the catchment. To review the performance of the model, UWRC recently recorded flow and depth of flow in the two drainage pipes (1050 mm diameter) just upstream of the catchment outlet during a storm event on July 1, 2006. These were compared with the catchment model results. Figures 2.2 and 2.3 shows the flow measurement during the event as well as the flow condition at the catchment outlet during the storm event Table 2.1 provides a summary of the monitored and modelled data associated with this event.



Figure 2-2 Flow Monitoring

Figure 2-3 Outflow from Catchment during July 1 Event (13:30 pm)

The above photograph clearly illustrates the low capacity of the system as well as the backwater effects the catch nets as causing. At the time of monitoring the total rainfall was only approximately 5 mm.



Table 2-1 Modelled vs Measured Flow Data at Catchment Outlet – July 1, 2006

Time Cumulative

rainfall

(mm)

Modelled

flow

(m3/s)

Modelled flow

depth

(m)

Measured

combined flow1

(m3/s)

Measured

flow depth2

(m)

11:30 0.8 0 0

12:00 2.0 0 0

12:30 3.4 0.01 0.04

13:00 4.8 0.13 0.18

13:30 5.4 0.55 0.34 0.66 0.52-0.63

14:00 6.6 0.77 0.4

14:30 7.4 0.69 0.37

15:00 7.6 0.7 0.38 Note: 1. measured combined flow represents a measured flow of 0.33 m3/s in each pipe 2. measured flow depth range represents the different flow depths in each pipe. Results from the model are reasonably within the range as measured for the storm event for flows. Measured flow depths are greater than those predicted by the model. This can be explained by the backwater effects created by the catch nets connected at the catchment outlet (see Figure 2.3). Based on the model results this influence is in the order of 200-300 mm for the storm event considered. Given the significant impact the nets have on the flow depth and the sensitivity of the drainage system to increased depths, further investigation may be warranted to determine the hydraulic impact for minor storm events.

2.3 Initial Modelling Initial modeling of the catchment without WSUD measures indicated flooding throughout the catchment even for frequent storm events (less than 1 year). This is mainly due to the flat slope of the catchment (typically 0.2 %). Two critical catchment flooding areas were identified along Crittenden Rd and at the intersection of Tapleys Hill Road and Meakin Tce. This also corresponds with findings from Tonkin (2003). Figure 2.4 presents an example of results obtained for a storm event on February 21, 1977.



Figure 2-4 Model Results - February 21, 1977

2.4 Modelling Methodology Due to the frequent nature of flooding in the catchment the modeling assessed the impact WSUD strategies have on the magnitude of flooding at the two critical points shown in Figure 2.4. For selected WSUD measures the following was undertaken:

1. Run model with and without WSUD measure implemented 2. For the two critical catchment points determine the peak flooding volume for each storm in the

25 year record 3. Rank each event from highest to lowest flooding volume 4. Undertake a frequency analysis to determine the flooding volume for varying return periods 5. Determine the percent reduction in flooding volume with the WSUD measure implemented for

varying return periods. The model assessed different WSUD systems for a range of storages with respect to the mean annual runoff volume (MARV). As a guide Figure 2.5 has been developed to illustrate the scales of each measure.

Critical flooding areas



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On-site raingarden

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Sedimentation basins

Modelled limits

On-site detentiontank

On-site rainwatertank

Allotment size

infiltration basins

Figure 2-5 Typical Operating Ranges for Devices Compared with Modelled Limits

The model developed considered the combined effect of devices evenly distributed across the catchment as well as catchment scale installations.

2.5 Distributed Infiltration/Filtration Devices Distributed infiltration (retention) and filtration (extended detention) devices include measures such as infiltration basins, bioretention devices, permeable pavements, gravel trenches, raingardens and tanks. These devices operate by either allowing stored water to infiltrate into the surrounding soil or be re-used (retention) or slow release (eg 12 to 24 hours) back to the drainage network (extended detention). The model simulated both retention and extended detention. Typically devices are distributed across the catchment at the allotment and/or streetscape level. To review the performance of each, model runs were performed for a range of catchment areas treated (5 to 40%) and a range of storages as a percentage of the mean annual runoff volume MARV (2.6 to 5.4 %, refer to Figure 2.4 previously). The MARV range would typically represent devices that treat 90% of the mean annual runoff (MARV=2.6%) and devices capable of retaining the 5 year 60 minute storm (MARV = 5.4%). This is based on an infiltration rate of 36 mm/hr and a device depth of 575 mm. Two examples of different sized devices at the allotment and streetscape level are provided below:

• A streetscape infiltration basin 40 m2 x 0.575 m deep with a connected impervious area = 2,350 m2 (refer to table 4.5 Report B – Water Quality, this device treats 90% of the mean annual runoff). Storage as a percentage of mean annual runoff = 2.6 % (based on Kent Town rainfall records).



• An allotment level raingarden with a total volume available = 3,450 litres and a connected impervious area of 162.5 m2 (this device retains the 5 year, 60 minute storm, taking into account an infiltration rate of 36 mm/hr). Storage as a percentage of mean annual runoff = 5.4 % (based on Kent Town rainfall records).

For the cases modelled the following curves were derived, indicating the reduction in flooding volume for various return periods and levels of catchment treated.

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5% catchment treated 2.6%MARV 10% catchment treated 2.6% MARV 20% catchment treated 2.6% MARV5% catchment treated 5.4% MARV 10% catchment treated 5.4% MARV 20% catchment treated 5.4% MARV40% catchment treated 5.4% MARV 40% catchment treated 2.6% MARV

Assumptions:1. Based on 6 minute rainfall data from Kent Town 1977-20022. Curves based on a 16 hour emptying time

Figure 2-6 Reduction in Flooding Volume vs Return Period - Crittenden Rd



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5% catchment treated 2.6% MARV 10% catchment treated 2.6% MARV 20% catchment treated 2.6% MARV5% catchment treated 5.4% MARV 10% catchment treated 5.4% MARV 20% catchment treated 5.4% MARV40% catchment treated 5.4% MARV 40% catchment treated 2.6% MARV

Assumptions:1. Based on 6 minute rainfall data from Kent Town 1977-20022. Curves based on a 16 hour emptying time

Figure 2-7 Reduction in Flooding Volume vs Return Period - Tapleys Hill Rd/Meakin Tce

The curves clearly indicate greater reductions in flooding volume for the lower return period storms. Devices with higher storages as a percent of the mean annual runoff (MARV) also provides greater flooding volume reductions (with the same discharge characteristics ie 16 hour emptying time in this case), particularly for treated catchment areas greater than 10%. It must be noted that allotment level devices would generally be installed on new or redeveloped allotments, thus limiting the overall amount of catchment that could be treated. In the current case the number of dwelling are expected to increase by 946 from the current 4,185 (Tonkin, 2003). The overall increase in connected impervious area throughout the catchment is expected to be in the order of 25 ha (based on 1,500 new dwellings), thus to maintain pre-redevelopment connected impervious area (ie regime-in-balance approach) the treated area as a percent of the total catchment would be approximately 20 %. If all impervious area from redeveloped sites was treated this value could be increased to approximately 25 % of the total catchment area.

2.6 Catchment Scale Infiltration Basins There may be opportunities to install infiltration basins throughout the catchment on land purchased, such as vacant allotments, specifically for this purpose. Runoff may then be directed to these sites from the main drainage network. Considering a typical vacant allotment size of 700 m2, with a maximum depth set at 1 m (total storage available = 700 kL), the following table can be used as a guide to the number of basins required to achieve varying levels of catchment treatment.



Table 2-2 Number of Infiltration Basins Required for Varying Areas of Catchment Treated

% of Catchment Treated Storage as a % of Mean Annual Runoff Volume (MARV)

2.6% 5.4%

5 0.85 1.85

10 1.7 3.7

20 3.4 7.4

40 6.8 14.8 Reductions in flooding volumes will not be as high as those for an equivalent distributed retention case. This has been observed in several studies undertaken by the UWRC, where increasing the number of retention storages to approximately 30 or more maximises the effectiveness of the retention storage (Pezzaniti et al 2004). This has been observed in the model.

2.7 Catchment ASR Schemes (Sized for Local Demand) The catchment level ASR schemes considered in Section 1.0 were also modelled to determine the reduction in flooding volume at Crittenden Rd and Tapleys Hill Rd/Meakin Tce. Only the holding storage necessary to enable each scheme to meet irrigation water requirements have been considered (refer to Table 1.2 previously). Figure 2.8 present results at Crittenden Rd and Tapleys Hill Rd/Meakin Tce considering implementation of the Powerhouse and Ledger oval ASR schemes and further implementation of the Matheson oval and Gleneagles reserve ASR scheme.

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Powerhouse + Ledger + Matheson + Gleneagles ASR - Tapleys Hill Rd/Meakin Tce

Powerhouse + Ledger ASR - Crittenden Rd

Powerhouse + Ledger - Tapleys Hill Rd/Meakin Tce

Assumptions:1. Based on 6 minute rainfall data from Kent Town 1977-20022. Minimum retention time = 72 hours3. Holding storages sized for local irrigation demand

Figure 2-8 Reduction in Flooding Volume vs Return Period



The above curves indicate the influence of upstream basins (eg Powerhouse and Ledger oval basins) is reduced at points further downstream in the catchment (ie at Tapleys Hill Rd/Meakin Tce). When compared with the distributed case similar reductions in flooding volume occur with 10 to 20% distributed retention/extended detention devices throughout the catchment.



3 CONCLUSIONS AND RECOMMENDATIONS

3.1 Harvesting and Re-use Catchment scale harvesting using ASR wetland schemes offer significant financial ($/kL) advantages compared to the combined effects of allotment level rainwater tanks. Catchment scale ASR wetland schemes will also enable sustainable long-term use of groundwater and offers additional benefits to the community such as water quality improvements, social amenity values and offer potential retail opportunities. When reviewing the total long term combined potential harvested volume for 1 kL rainwater tanks on redeveloped allotments, the maximum amount of water that could be harvested throughout the catchment at the ultimate state of development is approximately 34 ML/yr. This represents a net reduction in mains water demand to the entire catchment in the ultimate state of development of approximately 3 %. The combined tank storage throughout the catchment is approximately 1,500 kL. In the existing catchment there are potential opportunities for local ASR wetland schemes at the Powerhouse reserve, Ledger oval, Matheson reserve and Gleneagles reserve. It may be possible to consider a single large scheme, such as the Royal Adelaide golf course ASR, rather than several smaller schemes. The RAGC scheme could then be sized to harvest enough water to meet the equivalent total catchment demand on groundwater. That is water injected at RAGC can offset borewater extracted at any of the reserves in the catchment. There may also be the opportunity to utilize additional groundwater credit to reduce mains water open space irrigation. This would particularly be applicable for reserves that are not adjacent to the main drainage network, where diversion of catchment runoff may be difficult. Examples of such schemes occur in the Salisbury City Council area. Issues such as cost sharing would need to be considered. Although medium to large scale harvesting schemes (when available) offer advantages over allotment level rainwater tanks, allotment level schemes should not necessarily be discouraged as this promotes the culture of re-use. Larger scale schemes will typically not provide direct reticulation re-use opportunities to individual households and as such allotment level rainwater tank harvesting is still valid for Water Proofing Adelaide.

3.2 Flooding(minor events) Flooding difficulties in the catchment are frequent (less than 1 year ARI) and occur due to the low capacity of the drainage system as a result of the flat topography (typically 0.2%). Two critical flooding areas identified in the catchment occur at Crittenden Rd and Tapleys Hill Rd/Meakin Tce. Assessment of WSUD systems for flood benefit focused on potential reductions in flooding volumes at the two critical points. Most WSUD measures reviewed, which were sized for water quality only (eg treating 90% of mean annual runoff), provided low (<30%) to very low (<10%) reductions in flooding volume for the 5 year



ARI. Streetscape infiltration (retention) and filtration (extended detention) devices sized for a 5 year ARI distributed, across 20% or more of the catchment, enabled moderate (up to 50%) to high (50-75%) reductions in flooding volume. Allotment level raingardens installed on new or redeveloped allotments enabled moderate reductions. These reductions are improved for the more frequent events (eg 1 year ARI). With regards to WSUD, typically the most effective means of reducing flooding in the catchment using WSUD measures is associated with distributed infiltration (retention)/filtration (extended detention) devices, as opposed to storages at individual sites (for an equivalent storage volume). There may be opportunities to improve the effectiveness of such a strategy by zoning the catchment. This would require further study.



REFERENCES Argue, J., Allen, M., Geiger, W., Johnston, J., Pezzaniti, D., Scott, P., (2004). “Water Sensitive Urban Design: Basic Procedures for Source Control of Stormwater – A Handbook for Australian Practice”. First Edition. KBR (2004). “Metropolitan Adelaide Stormwater Management Study Part B –Stormwater Harvesting and Use Final Report”. Prepared by Kellogg Brown and Root Pty Ltd for the Metropolitan Adelaide Stormwater Management Steering Committee. Pezzaniti, D.; Argue, J.; Johnston, L. (2004). “Detention/Retention Storages for peak Flow Reduction in Urban Catchments: Effects of Spatial Deployment of Storages”. Australia Journal of Water Resources, 7(2), 131-138. Tonkin (2003). “Meakin Terrace Catchment – Initial Urban Stormwater Master Plan”. Prepared by Tonkin Consulting for the City of Charles Sturt. UWRC (2006). “Stormwater Detention Evaluation Project – Stormwater Modelling Final Report”. Prepared for the Campbelltown City Council, South Australia. UWRC (2006A). “Short Filed Monitoring and Evaluation Study of a Stormwater Mitigation Scheme for Water Re-Use Application”. Prepared for the Catchment Management Subsidy Scheme.

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