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Attachment B <br />Review and Recommendation of Analytical Methods for Estimating Ditch Efficiency <br />The following summarizes the results and recommendations for estimating ditch <br />efficiency based on a review of analytical methods, the data required for each method, <br />and the data readily available for the SPDSS basin-wide requirement. Several methods <br />were identified that have been developed use the same basic parameters. The following <br />parameters are used estimate conveyance efficiency: <br />• Seepage loss <br />• Canal length <br />• Canal geometry such as wetted perimeter or cross-sectional area <br />• Number of days water is in the ditch <br />• Diversion flow rate. <br />These methods generally use the same parameters but estimate seepage loss differently. <br />A commonly used methodology for estimating conveyance efficiency was published by <br />the SCS in the National Engineering Handbook (1993). The method estimates seepage <br />losses as a function of material type, flow, and incidental vegetation losses. <br />Worstell (1976) developed an empirical estimate of seepage rates or conveyance losses <br />that was dependent upon the predominant soil type of the canal as well as the longitudinal <br />area of the canal (i.e., the product of the wetted perimeter and canal length). The seepage <br />rate estimates were based on numerous studies that utilized ponding tests as the <br />predominant method for determining seepage losses. <br />Swamee et al. (2000) developed a method to estimate seepage loss based upon the <br />hydraulic conductivity of the soil and the width-to-depth ratio of the canal. The premise <br />of the analysis is that the depth to the water table is large and that the soils are <br />homogenous and isotropic. <br />The SCS, Worstell (1976), and Swamee et al. (2000) are all appropriate for estimating <br />efficiencies for an individual ditch system when the parameters listed above are known. <br />However, they are not recommended for use in the SPDSS basin-wide analysis because <br />the canal geometry, required for wetted perimeter or width-to-depth ratio, is generally not <br />known and cannot be easily estimated. The data-centered approach used for the historic <br />crop consumptive use analysis requires information to be developed or estimated basin- <br />wide using available data, GIS coverages, or HydroBase. <br />Since there is limited information available pertaining to conveyance efficiency for most <br />of the key structures within the South Platte basin, the existing information that was <br />available was used to develop a simplified approach. Nineteen major ditch systems <br />throughout the South Platte Basin were selected for further analysis based on the <br />availability of: <br />Page B1 of B9 <br />