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Explanation and Use of the Blaney-Criddle Reuse Water Balance Model <br />A Microsoft Excel Ver. 4.0 Spreadsheet <br />OVERVIEW OF MODEL: <br />The Blaney-Criddle water balance model is a straight forward water balance model with the <br />addition of vegetation water consumption. Evaporation, rain, effluent flow, and pond leakage <br />form the basic aspects of the model, however the critical portion of the model is the Blaney- <br />Criddle plant water consumption calculation. <br />Blaney and Criddle in the early 1960's worked on the quantitative estimation of vegetation water <br />usages. This leads to the Blaney-Criddle method. The Blaney-Criddle formula is that the <br />consumptive use (U) is equal to a seasonal coefficient (K) times a monthly consumptive use <br />factor(F) (U=K*F). The monthly consumptive use factor (F) is a function of the mean monthly <br />temperature in degrees Fahrenheit (t) times the monthly percent of day-time hours (p) divided by <br />100, expressed as (F= t*p/100). K is a factor relating the plant water usage for a specific species. <br />K factors are generated under experimental conditions where F and U in the above formula are <br />measured under tightly controlled conditions (K=U/F). <br />DATA ENTRY: <br />Data entry is divided into distinct parts of the spreadsheet. The basic facility data is entered into a <br />block at the top left of the spreadsheet. The entry locations are highlighted with light green <br />stippling to designate which cells of the spreadsheet are designed for the input of information. All <br />other cells are calculated and should be protected from change. In the basic facility information <br />block there are spaces to enter the facility name, its location, the daily average facility flow rate, <br />the yearly evaporation rate, the acreage of ponds (and other free water surfaces), and the acreage <br />of land to be irrigated.