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| <div class="col-md-8"> | | <div class="col-md-8"> |
| {{TOClimit|2}} | | {{TOClimit|2} |
| | [[File:Cistern Size.png|thumb|Schematic diagram of the inputs and outputs to a rainwater harvesting cistern]] |
| | ===Simple=== |
| | Five percent of the average annual yield can be estimated: |
| | <br><strong>Y<sub>0.05</sub>= A × C<sub>vol, A</sub> × R<sub>a</sub> × e × 0.05</strong> |
| | <br>Y<sub>0.05</sub> = Five percent of the average annual yield (L) |
| | <br>A = The catchment area ( m<sup>2</sup>) |
| | <br>C<sub>vol, A</sub> = The annual runoff coefficient for the catchment |
| | <br>R<sub>a</sub> = The average annual rainfall depth (mm) |
| | <br>e = The efficiency of the pre-storage filter |
| | *Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information. |
| | *In a study of three sites in Ontario, STEP found the annual C<sub>vol, A</sub> of the rooftops to be around 0.8 [http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. This figure includes losses to evaporation, snow being blown off the roof, and number of overflow events. |
|
| |
|
| ====Rapid====
| | Five percent of the average annual demand (D<sub>0.05</sub>) can be estimated: |
| <p>Five percent of the average annual yield can be estimated:
| | <br><strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong> |
| <br><strong>Y<sub>0.05</sub>= A × C<sub>vol, A</sub> × R<sub>a</sub> × e × 0.05</strong>
| | <br>D<sub>0.05</sub> = Five percent of the average annual demand (L) |
| <br>Y<sub>0.05</sub> = Five percent of the average annual yield (L)
| | <br>P<sub>d</sub> = The daily demand per person (L) |
| <br>A = The catchment area ( m<sup>2</sup>)
| | <br>n = The number of occupants |
| <br>C<sub>vol, A</sub> = The annual runoff coefficient for the catchment
| |
| <br>R<sub>a</sub> = The average annual rainfall depth (mm)
| |
| <br>e = The efficiency of the pre-storage filter
| |
| <ul>
| |
| <li>Filter efficiency (e) can be reasonably estimated as 0.9 pending manufacturer’s information. </li>
| |
| <li>In a study of three sites in Ontario, STEP found the annual C<sub>vol, A</sub> of the rooftops to be around 0.8 [http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. This figure includes losses to evaporation, snow being blown off the roof, and number of overflow events.</li>
| |
| </ul>
| |
| </p>
| |
| <p>Five percent of the average annual demand (D<sub>0.05</sub>) can be estimated:
| |
| <br><strong>D<sub>0.05</sub> = P<sub>d</sub> × n × 18.25</strong>
| |
| <br>D<sub>0.05</sub> = Five percent of the average annual demand (L)
| |
| <br>P<sub>d</sub> = The daily demand per person (L)
| |
| <br>n = The number of occupants
| |
| </p>
| |
| ---- | | ---- |
| <p>Then the following calculations are based upon two criteria:
| | Then the following calculations are based upon two criteria: |
| <ol>
| | #A design rainfall depth is to be captured entirely by the RWH system. |
| <li>A design rainfall depth is to be captured entirely by the RWH system.</li>
| | #The average annual demand (D) is greater than the average annual yield (Y) from the catchment. |
| <li>The average annual demand (D) is greater than the average annual yield (Y) from the catchment. </li>
| | When Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.33, the storage volume required can be estimated: |
| </ol>
| | <br><strong>V<sub>S</sub> = A × C<sub>vol</sub> × R<sub>d</sub> × e</strong> |
| </p>
| | <br>V<sub>S</sub> = Storage volume required (L) |
| <p>When Y<sub>0.05</sub>/ D<sub>0.05</sub> < 0.33, the storage volume required can be estimated:
| | <br>A = The catchment area (m<sup>2</sup>) |
| <br><strong>V<sub>S</sub> = A × C<sub>vol</sub> × R<sub>d</sub> × e</strong>
| | <br>C<sub>vol, E</sub> = The design storm runoff coefficient for the catchment |
| <br>V<sub>S</sub> = Storage volume required (L)
| | <br>R<sub>d</sub> = The design storm rainfall depth (mm), and |
| <br>A = The catchment area (m<sup>2</sup>)
| | <br>e = The efficiency of the pre-storage filter. |
| <br>C<sub>vol, E</sub> = The design storm runoff coefficient for the catchment
| | /*Good catchment selection means that the runoff coefficient, for a rainstorm event (C<sub>vol, E</sub>) should be 0.9 or greater. |
| <br>R<sub>d</sub> = The design storm rainfall depth (mm), and
| | |
| <br>e = The efficiency of the pre-storage filter.
| | When 0.33 < Y<sub>0.05</sub>/ D<sub>0.05</sub>< 0.7, the total storage required can be estimated by adding Y<sub>0.05</sub>: |
| <ul>
| | <br> |
| <li>Good catchment selection means that the runoff coefficient, for a rainstorm event (C<sub>vol, E</sub>) should be 0.9 or greater.</li>
| | <strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong> |
| </ul> | |
| </p>
| |
| <p>When 0.33
| |
| < Y<sub>0.05</sub>/ D<sub>0.05</sub>
| |
| < 0.7, the total storage required can be estimated by adding Y<sub>0.05</sub>:
| |
| <br>
| |
| <strong>Total storage = V<sub>S</sub> + Y<sub>0.05</sub></strong>
| |
| </p>
| |
| ---- | | ---- |
| </div>
| | ===STEP Rainwater Harvesting Tool=== |
| <div class="col-md-4">
| | [[File:RWH_tank_capacity_table.jpg| Quick reference table generated using STEP RWH tool, (data for the City of Toronto (median annual rainfall 678 mm). Optimal cistern size is that providing at least a 2.5% improvement in water savings following an increase of 1,000 Litres in storage capacity.]] |
| <panelWarning>
| | The Sustainable Technologies Evaluation Program have produced a rainwater harvesting design and costing tool specific to Ontario. The tool is in a simple to use Excel format and is free to download. |
| <gallery mode="packed" widths=300px heights=300px>
| |
| Cistern Size.png| Schematic diagram of the inputs and outputs to a rainwater harvesting cistern
| |
| </gallery>
| |
| </panelWarning>
| |
| </div>
| |
| <div class="col-md-12">
| |
| | |
| ====STEP Rainwater Harvesting Tool====
| |
| </div>
| |
| <div class="col-md-8">
| |
| <p>The Sustainable Technologies Evaluation Program have produced a rainwater harvesting design and costing tool specific to Ontario. The tool is in a simple to use Excel format and is free to download.</p>
| |
| <strong>[http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/rainwater-harvesting-design-and-costing-tool/| Rainwater Harvesting Tool]</strong> | | <strong>[http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/rainwater-harvesting-design-and-costing-tool/| Rainwater Harvesting Tool]</strong> |
| </div>
| |
| <div class="col-md-4">
| |
| <panelWarning>
| |
| <gallery mode="packed" widths=300px heights=300px>
| |
| RWH_tank_capacity_table.jpg| Quick reference table generated using STEP RWH tool, (data for the City of Toronto (median annual rainfall 678 mm). Optimal cistern size is that providing at least a 2.5% improvement in water savings following an increase of 1,000 Litres in storage capacity.
| |
| </gallery>
| |
| </panelWarning>
| |
| </div>
| |
| <div class="col-md-12">
| |
| ---- | | ---- |
| | | ===STEP Treatment Train Tool=== |
| ====STEP Treatment Train Tool====
| | Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system could be integrated into a site plan using STEP's Treatment Train Tool. |
| <p> Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system could be integrated into a site plan using STEP's Treatment Train Tool.
| |
| In a typical configuration: | | In a typical configuration: |
| <ul>
| | *The catchment (roof) would be 100% impervious |
| <li>The catchment (roof) would be 100% impervious</li>
| | *The rainwater harvesting system would be a 'Storage' Element with the following properties: |
| <li>The rainwater harvesting system would be a 'Storage' Element with the following properties:</li>
| | **Storage type = No removal |
| <ul>
| | **Lined |
| <li>Storage type = No removal</li>
| | **Underlying soil = <em>doesn't matter, can ignore</em> |
| <li>Lined</li>
| | **Evaporation factor = 0 |
| <li>Underlying soil = <em>doesn't matter, can ignore</em></li>
| | **Suction head (mm) = 0 |
| <li>Evaporation factor = 0</li>
| | **Saturated conductivity (mm/hr) = 0 |
| <li>Suction head (mm) = 0</li>
| | **Initial soil moisture deficit (fraction) = 0 |
| <li>Saturated conductivity (mm/hr) = 0</li>
| | *The dimensions of the rainwater cistern can be placed into the fields: |
| <li>Initial soil moisture deficit (fraction) = 0</li>
| | #Bottom elevation (m) |
| </ul>
| | #Maximum depth (m) |
| The dimensions of the rainwater cistern can be placed into the fields: | | #Initial water depth (m) |
| <ol>
| | #The Curves table is designed to accommodate ponds of roughly conical dimensions. A rainwater cistern is usually cuboid or cylindrical in shape, so that the area (m<sup>2</sup>) will remain the same throughout the depth. |
| <li>Bottom elevation (m)</li>
| |
| <li>Maximum depth (m)</li>
| |
| <li>Initial water depth (m)</li>
| |
| <li>The Curves table is set up to accommodate ponds of roughly conical dimensions. A rainwater cistern is usually cuboid or cylindrical in shape, so that the area (m<sup>2</sup>) will remain the same throughout the depth. </li>
| |
| </ol>
| |
| </ul>
| |
| </p>
| |
| <strong>[http://www.sustainabletechnologies.ca/wp/low-impact-development-treatment-train-tool/|The Treatment Train Tool]</strong> | | <strong>[http://www.sustainabletechnologies.ca/wp/low-impact-development-treatment-train-tool/|The Treatment Train Tool]</strong> |
| ---- | | ---- |
| [[category:modeling]] | | [[category:modeling]] |