Using Graywater and Stormwater to Enhance Local Water Supplies An Assessment of Risks, Costs, and Benefits (2016) / Chapter Skim
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Appendix A: Calculating the Benefits of Rooftop Runoff Capture Systems
Appendix A: Calculating the Benefits of Rooftop Runoff Capture Systems
Pages 187-200
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From page 187... ...
The main data required for the analyses in this rewas supplied by previously stored roof runoff water in stor- port included rain data for the six locations examined (from age tanks. Toilet flushing requirements were based on typical NOAA weather stations)
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From page 188... ...
However, the data are not intend ed as definitive predictions or as a basis for design guidance. TABLE A-1 Comparison of Precipitation Annual Rain Totals and Rain Counts Between the Scenario Analysis Calculation Period and the Long-term Rainfall Record Los Angeles, CA Seattle, WA Lincoln, NE Madison, WI Birmingham, AL Newark, NJ Long-term rain record 1948-1999 1965-2012 1973-1999 1948-1999 1948-1999 1948-1999 (1995 gap)
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From page 189... ...
Annual Number of Rains 110 35 100 30 90 25 80 20 70 15 60 1 2 1973-1999 1996-1999 1 1973-1999 2 1996-1999 1: 1973 through 1999 X Data 2: 1996 through 1999 FIGURE A-1 Comparisons of the period of record with the scenario analysis period in terms of annual rain depth and number of rainfall events per year.
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From page 190... ...
100 Annual Rain Count 50 80 40 60 30 20 40 10 20 1 1949-1999 2 1 1949-1999 2 1995-1999 1995-1999 Newark Rains 1: 1949 through 1999 2: 1995 through 1999 70 140 Newark Newark 60 130 Total Annual Rain Depth (in) Rain Count per Year 120 50 110 40 100 30 90 20 80 1 2 1 1949-1999 2 1949-1999 1995-1999 1995-1999 1: 1949 through 1999 FIGURE A-1 Continued 2: 1995 through 1999
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From page 191... ...
suitable source for the collected water is from the building roofs because of its generally better water quality, high unit ROOF RUNOFF CALCULATIONS area runoff yield, and elevation above storage tanks and irrigated land. The landscaped areas represent the amount of The following sections describe an example set of calarea that can be irrigated with the harvested roof runoff wa- culations used to develop the analyses used in this report.
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From page 192... ...
Therefore, for roof runoff harvesting. Most of the runoff volumes in this the whole area, the total flow-weighted annual Rv is: 7.70 𝑖𝑖 𝑖𝑖 𝑖𝑖ℎ𝑒𝑒𝑒𝑒 = 0.45 medium-density residential land use analysis originated 16.73 𝑖𝑖 𝑖𝑖 𝑖𝑖ℎ𝑒𝑒𝑒𝑒 from the street and roof areas, with smaller (and about equal amounts)
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From page 193... ...
Minimum 0.01 79 41 23 15 0 0 0.02 0.01 Maximum 3.5 716,277 226,403 83,501 53,679 219,291 133,402 0.56 1.53 Average 0.51 85,703 31,728 10,152 6,527 29,112 8,184 0.47 0.75 Total 83.67 13,969,610 5,170,000 1,655,000 1,064,000 4,745,000 1,334,000 n/a 45.18 TABLE A-6 Overall Summary of Runoff Volume Contributions by Source Area and Month for Los Angeles Medium Density Residential Areas Land Use Sidewalks/ Small Five-Year Average Flows by Month Rain Total (in.) Totals Roofs Driveways Walks Street Area Landscaped Area Area (% of total land use)
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From page 194... ...
prepared a cations, as shown on Table A-7. The ETo values are given summary of crop coefficients for the Southwest Florida Wain inches/day and were therefore converted to inches/month ter Management District and the Florida Agricultural Experifor direct comparison to the monthly rainfall (or soil mois- ment Station, which lists turfgrass coefficients for warm and ture addition)
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From page 195... ...
(2001) presented a summary each of these locations, which were then used in the model for arid areas with turfgrass coefficients ranging from about to calculate the effects of storage and roof runoff volumes 0.8 to 0.9.
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From page 196... ...
The averWinSLAMM corresponding to typical runoff harvesting sce- age domestic water savings by using harvested roof runoff narios. Table A-17 shows the storage volume calculations for for this scenario analysis is therefore: the two water storage tank options examined, shown for the 11.6% 𝑀𝑀𝑀𝑀𝑀𝑀 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 27,940 𝑓𝑓𝑓𝑓 3 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 3,241 𝑓𝑓𝑓𝑓 3 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 ∗ = 100 𝑎𝑎𝑐𝑐𝑐𝑐𝑐𝑐 − 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 − 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 Los Angeles example.
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From page 197... ...
Table A-18 summarizes the monthly Los Angeles water uses for the three water demand scenarios examined in VERIFICATION OF ORIGINAL ANALYSIS the report: conservation irrigation, toilet flushing, and conservation irrigation plus toilet flushing combined. Table The committee performed several levels of verification A-19 shows the calculated potential water savings from the on this original analysis of water savings potential to ensure WinSLAMM model for the 5 years of rainfall data in a Los that the results are sound.
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From page 198... ...
Newark irrigation requirements, 0 0 0 0 0.328 1.14 0.16 1.32 0 0 0 0 2.948 ignoring excessive rainfall periods (in/mo) TABLE A-15 Example Watershed Demand and Available Stormwater by Land Use in Los Angeles ft3 of irrigation water/acre/mo Total Annual Total Total Landscaped Irrigation Annual Annual Area (% of Demand to Roof Land Use total land Meet ET Runoff Runoff use)
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From page 199... ...
Landscaped area (ac per 100 ac of MDR) 52.5% 𝑜𝑜𝑜𝑜 100 𝑎𝑎𝑎𝑎𝑎𝑎𝑒𝑒𝑠𝑠 = 52.5 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 TABLE A-18 Average Monthly Water Use Patterns for Los Angeles Scenario Gallons/day/100 ac Medium- Southwest Minimum Irrigation Southwest Toilet Southwest Minimum Irrigation Density Residential (MDR)
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From page 200... ...
a Average annual volume of potable water replaced 323,729 366,510 438,136 by roof runoff using water tank (ft3 per year/100 ac) Average annual volume of potable water replaced 2.42 2.74 3.28 by roof runoff using water tank (Mgal/yr/100 ac)
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