Stream: Cebolla Creek (Lower Segement) Executive Summary

Home Browse Search

BLM 1 10/8/2008 1 35.10 1 87.8-14.0 1 17.10 1 14.13 The summer flow recommendation, which met 3 of 3 criteria and is within the accuracy range of the R2CROSS model is 26.0 cfs. The summer flow recommendation was derived by averaging the results of the data sets. The shoulder period from October 1 — November 15 was lowered from 26.0 cfs to 22.0 cfs because of water availability constraints. The winter flow amount, which meets 2 of 3 criteria, is 14.1 cfs but the recommend amount has been lowered to 13.5 cfs due to water availability constraints. Hydrologic Data and Analysis After receiving the cooperating agency's biologic recommendation, the CWCB staff conducted an evaluation of the stream hydrology to determine if water was physically available for an instream flow appropriation. This evaluation was done through a computation that is, in essence, a "water balance ". In concept a "water balance" computation can be viewed as an accounting exercise. When done in its most rigorous form, the water balance parses precipitation into all the avenues water pursues after it is deposited as rain, snow, or ice. In other words, given a specified amount of water deposition (input), the balance tries to account for all water depletions (losses) until a selected end point is reached. Water losses include depletions due to evaporation and transpiration, deliveries into ground water storage, temporary surface storage, incorporations into plant and animal tissue and so forth. These losses are individually or 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 together 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 Cebolla Cr — Lower no such gage is available at the LT; although flows have been gaged on Cebolla Creek. A gage was located in the upstream reaches (Cebolla Cr. nr Lake City) and two were in very downstream positions (Cebolla Cr. near Powderhorn and Cebolla Cr. at Powderhorn). However, the data from these gages is of limited value being both old and a short Period of Record (POR). While the use of some of this data might be possible, it made sense to examine nearby drainages for gages with better data records that could serve as "representative" gage stations. -4-