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<br />. <br /> <br />. <br /> <br />The incremental reach runoff was determined by taking the difference of the total volumetric runoff <br />between successive USGS gage locations, The development of initial proration factors is <br />summarized in Appendix C, Section 6.4, A table of the original pre-calibration proration factors <br />(based on drainage area and mean annual precipitation) can be found in Appendix C, Section 6.5, <br />Additional baseflow points were added during the calibration phase to provide greater resolution in <br />determining the quantity of water available from the stream at a specific location, <br /> <br />At several locations, the prorated hydrograph developed using the incremental reach gain showed an <br />attenuated shape that was not representative of the "natural" hydrograph shape. This occurred <br />predominantly in the headwater areas where the hydrograph is dominated by runoff from spring <br />snow melt. In these situations, the proration factor was determined as a function of a stream gage in a <br />neighboring tributary, by comparing the local drainage areas and average precipitation values, Using <br />this technique, both the correct volume and shape of the hydrograph were distributed into the <br />ungaged headwater tributary. <br /> <br />The final proration factors for the StateMod implementation for the San Juan River basin can be <br />found in Appendix A, sanjuan.rib. <br /> <br />"'.." ;.. <br /> <br />River System <br />a32fYwrpdQcs/slUljUQrV4.0-/.doc 9/15/96 <br /> <br />4-6 <br />