23.72.070 WATER BUDGET CALCULATIONS.
The project applicant may elect to complete a water budget calculation for the landscape project. Water budget calculations, if prepared, shall adhere to the following requirements:
(a) The plant factor used shall be from WUCOLS or from horticultural researchers with academic institutions or professional associations as approved by the California Department of Water Resources (DWR). The plant factor ranges from 0.0 to 0.3 for low water use plants, from 0.4 to 0.6 for moderate water use plants, and from 0.7 to 1.0 for high water use plants.
(b) All water features shall be included in the high water use hydrozone.
(c) All special landscape areas shall be identified and their water use included in the water budget calculations.
(d) The reference evapotranspiration adjustment factor for special landscape areas shall not exceed 1.0. The ETAF for all other landscaped areas shall not exceed 0.55 for residential areas and 0.45 for nonresidential areas. ETo values from the reference Evapotranspiration Table, as provided by the City, shall be used in calculating the maximum applied water allowance (MAWA) and estimated total water use (ETWU).
(e) For the purpose of determining estimated total water use, average irrigation efficiency is assumed to be 0.75 for overhead spray devices and 0.81 for drip system devices.
(f) Maximum applied water allowance (MAWA) shall be calculated using the equation below:
(1) MAWA = (ETo) (0.62) [(0.7 x LA) + (0.3 x SLA)]
(2) MAWA = (ETo) [(0.45 x LA) = (0.55 x SLA)] for nonresidential areas
MAWA = Maximum applied water allowance (gallons per year)
ETo = Reference evapotranspiration (inches per year)
0.62 = Conversion factor (to gallons)
0.55 = Reference evapotranspiration adjustment factor (ETAF) for residential area
0.45 = Reference evapotranspiration adjustment factor (ETAF) for nonresidential areas
LA = Landscape area including SLA in residential areas
0.3 = Additional water allowance for SLA in nonresidential areas
SLA = Special landscape area (square feet).
(g) A local agency or project applicant may consider effective precipitation (25% of annual precipitation) in tracking water use and may use the following equation to calculate the MAWA:
(1) MAWA = (ETo - Eppt) (0.62) [(0.55 x LA) + (0.45 x SLA)] for residential areas
(2) MAWA = (ETo - Eppt) (0.62) [(0.45 x LA) + (0.55 x SLA)] for nonresidential areas
(h) Estimated total water use (ETWU) will be calculated using the equation below. The sum of the ETWU calculated for all hydrozones will not exceed the MAWA.
ETWU = (ETo)(0.62)(PF x HA) + SLA]
ETWU = Estimated total water use per year (gallons)
ETo = Reference evapotranspiration (inches)
PF = Plant factor from WUCOLS
HA = Hydrozone area (high, medium, and low water use areas) (square feet)
SLA = Special landscape area (square feet)
0.62 = Conversion factor
IE = Irrigation efficiency (minimum 0.70) equals 0.75 for overhead spray devices and 0.81 for drip system devices