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<br /> <br />Redwood City Public Works Services <br />Customer Water Use Website RFP <br />Attachment B – Water Budget Methodolgy 2 <br />ERain = Effective rainfall (inches) equals the depth of rain effective in <br />offsetting ETo for each hydrozone. Effective rainfall varies <br />widely with rainfall frequency, magnitude, time of year, and <br />root zone depth. Redwood City uses rainfall data from Weather <br />Underground (WU). WU data is accessed through the WU API <br />more information is available at <br />http://www.wunderground.com/weather/api <br />by <br />WeatherUnderground <br />(period aggregate) <br />NIR Net Irrigation Requirement: The amount of water required in a <br />hydrozone that is not provided by rainfall. NIR is calculated for <br />each day, based on weather data downloaded from specified <br />weather websites. NIR is calculated for both turf and non-turf <br />surfaces, since these surfaces have different water storage <br />characteristics, and thus differing requirements for irrigation. <br />NIR is a function of daily precipitation and daily reference <br />evapotranspiration. <br />Function >= 0 <br />IE = <br /> <br />Irrigation Efficiency measures the percent of applied water that <br />is beneficially used by plants. All irrigation systems have some <br />inefficiencies as water is lost as runoff, overspray, or percolates <br />past the root zone. <br />IET or IEN <br />IET = Irrigation Efficiency for Turf (value determined and inputted by <br />Redwood City) <br />i.e. 0.5 to 0.65 <br />IEN = Irrigation Efficiency for Turf default value 0.8 <br />C1 = Conversion factor putting the water budget into gallons. 0.623 <br />C2 = Conversion factor putting the water budget in into hundred <br />cubic feet (ccf). <br />748 <br />R = Number of fulltime residents (default = 2, provided by <br />customer and validated by City) <br />2 <br />RW Volume of water allocated to 1 resident per day 57.6 <br />DPP = Days per period is the total days in a billing <br />period/consumption cycle (when calculating a budget for a <br />single day DPP = 1) <br />calculated <br />SN= Special Needs in gallons per day <br /> <br />Net Irrigation Requirement Function: <br />NIRT is calculated for turfgrass using the logic below and the max soil constant for turf. <br />NIRN is calculated for non-Turf using the logic below and the max soil constant for non-turf <br /> <br />NIR(d) = ETo(d) - ERain(d) - SoilStorage(d-1) minimized to 0, where <br />ERain(d) = Min(Precip(d), (MaxSoilConstant + ETo(d) - SoilStorage(d-1))) <br />SoilStorage(d) = Min(MaxSoilConstant, (Precip(d) - ETo(d) + SoilStorage(d-1))) minimized to 0 <br />Precip(d) = Rainfall for day d, measured using tipping bucket rain gauges <br />6.1.E. - Page 55