2-08CW056 Supplemental Data - Laserfiche WebLink

Home Browse Search

0 0 collectively subtracted from the input to reveal the net amount of stream runoff as represented by the discharge measured by stream gages. Of course, the measured stream flow need not be the end point of interest; indeed, when looking at issues of water use to extinction stream flow measurements may only describe intermediate steps in the complex accounting process that is a water balance carried out to a net value of zero. In its analysis, CWCB staff has attempted to use this idea of balancing inputs and losses to determine if water is available for the recommended Instream Flow Appropriation. Of course, this analysis must be a practical exercise rather than a lengthy, and costly, scientific investigation. As a result, staff has simplified the process by lumping some variables and employing certain rational and scientifically supportable assumptions. The process may be described through the following description of the steps used to complete the evaluation for this particular stream. The first step required in determining water availability is a determination of the hydrologic regime at the Lower Terminus (LT) of the recommended ISF reach. In the best case this means looking at the data from a gage at the LT. Further, this data, in the best case, has been collected for a long period of time (the longer the better) including wet and dry periods. In the case of Severy Creek no such gage is available at the LT. In fact, there is no gage on Severy Creek. It is thus necessary to describe the normal flow regime at the Severy Creek LT through a "representative" gage station. The gage station selected for this was NORTH CASCADE CREEK (discharge measured by Colorado Springs Utilities), a gage with an available 57 year period of record (POR) collected between 1949 and 2006. The gage is at an approximate elevation of 8840 ft above mean sea level (amsl) and has a drainage area of 1.9 mil. The hydrograph (plot of discharge over time) produced by this gage was used on Severy Creek by multiplying the North Cascade discharge values by the ratio of Severy Creek basin area (3.40 mi above the LT) to North Cascade Cr. basin area (1.91 mi2). No adjustments for losses to diversions were needed in either basin in this case allowing for a direct computation of the hydrograph. The following hydrograph depicts the mean monthly discharge of Severy Creek (proportioned off North Cascade Creek). Included in the hydrograph are the recommended ISF values. The data used in the creation of this hydrograph are displayed in Table #2.