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e e e a-',~'''~'J Accourilibl!' Iiyllrolo~: Non-Consumed Precipitation is defined as 1he precipitation that would have resulted in runoff had the reservoir not been constructed, and the remainder of the precipitation is consumed by plants, trees, and other types of vegetation. As a matter of example, utilize 30% of precipitation that results in runoff and 70% consumed by vegetation. Unless a site-specific study has been conducted for the reservoir area, the State of Colorado utilizes 30% as the Non-Consumed Precipitation standard, The State of Colorado allows the Reservoir owner to retain the portion of precipitation tnat would nave gone to the plants (i.e. 70%) and the runoffponion (i.e. 30%) must be returned to the river if out of priority. If the plant consumed portion of the precipitation is kept in the reservoir and the evaporation pan is at tbe reservoir site, the foUowing equation applies: Adjusted Gross Evaporation = Net Evaporation + Precipitation - (0.3 x Precipitation) Adjusted Net Pan Evaporation = Gross Pan Evaporation - Precipitation + (0.3 x Precipitation) Adjusted Net Reservoir Evaporation = ((0.7 x Hook Reading) + (0.3 x Precipitation)) x Reservoir Area If the plant consumed ponion of the precipitation is kept in the reservoir and the evaporation pan is WI! at tbe reservoir site, the following equation applies: Adjusted Net Reservoir Evaporation = [(0.7 x (Hook Reading + Precipitation at the evaporation pan site)) + (0.3 x Precipitation at the evaporation pan site)] -[ Precipitation at the Reservoir site + (0.3 x Precipitation at the Reservoir site)] x Reservoir Area The reservoir water volume balance equation for the Accounting Hydrology is: Change in storage = Inflow - Release - Adjusted Net Reservoir Evaporation Computed Inflow = Change in Storage + Release + Adjusted Net Reservoir Evaporation Example: Change in Storage = 100 a.[ Reservoir Release = 200 a.[ Hook Reading = 2 inches Precipitation = I inch Reservoir Surface Area = 500 acres Computed Inflow = 100 + 200 + [((0.7 x 2) + (0.3 x I)) x i/I2 x 500] = 37083 a.[ The difference the evaporation and computed inflow for the physical hydrology and the accounting hydrology in the example above is: .. Evaporation Difference = Accounting Evaporation - Physical Evaporation = 70.83 - 5833 = 12.5 a.f. Computed Inflow Difference = Accounting Compo Inf - Physical Compo lnf = 370.83 - 358.33 = 12.5 a.[