Stream: Tabeguache Creek (Lower Segement) Executive Summary

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mean sea level (amsl) and has a drainage area of 1,069 mil. (Data for this station was modified by removal of data from the San Miguel River near Nucla basin gage to isolate the representative portion of the basin and reduce the effective drainage basin size to 420 mi2.) While the hydrograph (plot of discharge over time) produced from these gages includes the consumptive use of numerous upstream diversions, the diversions do not preclude the use of the data from the gage. To make the measured data transferable to Tabeguache Creek — Lower above the LT, the consumptive portions of diversions were added back to the measured hydrograph. The "adjusted" hydrograph that resulted could be used on Tabeguache Creek - Lower above the LT by multiplying the "adjusted" gage discharge values bey an area ratio; specifically, the area of Tabeguache Creek — Lower above the LT (151.97 mi) to San Miguel River at Naturita, CO (modified) (420 mi2). The resulting proportioned hydrograph was itself "adjusted" to reflect the consumptive irrigation depletions (decreased) and out -of -basin diversions (decreased) that occur upstream of Tabeguache Creek — Lower above the LT. The final hydrograph thus represents a distribution of flow over time that has been reduced to reflect existing human uses. {The Following discussion is based upon the US Geological Survey's Techniques of Water - Resources Investigations Series, Book 4: Hydrologic Analysis and Interpretation, Chapter A3: Statistical Methods in Water Resources (Chapter 3: Describing Uncertainty) by D.R. Helsel and R. M. Hirsch. This technical reference provides the scientific background and guidance important to the systematic interpretation of hydrologic data. The document is available online and is a valuable aid to understanding and interpreting the analyses described here.} The next step in producing a representation of the discharge at Tabeguache Creek — Lower above the LT was to compute the Geometric Mean of the area- prorated data values from the San Miguel River at Naturita, CO (modified) Hydrograph. This step is of value because of the inherent statistical weaknesses found in any collection of data intended to measure natural stream discharge. Without getting into the details of statistical theory, it is worth noting that a set of discharge measurements is inherently inaccurate, no matter how well collected, due to the difficulties attendant to data collection, especially hydrologic data. In this particular case, the short period of record lends even greater merit to the use of this statistical tool. To give deference to this fact and to increase the value of the hydrograph product of this analysis, the Geometric Means of the data were computed and plotted along with the 95% Confidence Intervals about the data. The resultant hydrograph, including recommended Instream Flow values, is displayed in Figure 1 with the data displayed in Table 2. -5-