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<br />~{/~~/L~~q iL:8i <br /> <br />'::I t t1L::~'::I(j lOC; <br /> <br />W~ibHI WAI~~ ~Nb iNG <br /> <br />t-'AIj~ 1::J;j <br /> <br />'"In'" 79' <br />vel't <br /> <br />composition is a conglomerate of gravel, sand, and loam. Hay Gulch, Cherry Creek, and Long Hollow <br />are the three major tributaries in this section of the La Plata River and there are 13 diversions between <br />Hesperus and the stateline. . <br /> <br />Consumptive Use Analysis <br /> <br />Determining the amount of water consumed by the native vegetation along the La Plata River corridor is. <br />dependent upon the plant species, thickness of the foliage canopy, density of cover, depth to water table, <br />and climate. In September 2000, staff from the Division VII Office in Durango conducted a field <br />vegetation survey to quantify the type, density, and percentage of vegetation in six designated stream <br />reaches. Vegetation was segmented into three general categories: <br />. Trees - including Russian Olive, Cottonwood, and Poplar <br />· Brush - including Willows, Tamarisk, and Sage brush <br />. Herbaceous cover - including Wire grass, Blue grass, Brome, Clover, Rice grass, Kosha, Johnson <br />grass, Chicory, Fox tail, Cheat grass, Spotted lmap, Diffused Imap, and Russian knap. <br /> <br />Vegetative density is a function of two elements - thickness of foliage canopy and density of cover and is <br />expressed qualitatively as a percentage ofland cover2. The amount ofland or acreage inundated by <br />phreatophytes in the La Plata River watershed for the designated area of study was quantified by <br />planimetering a series of 1981 NRCS aerial photographs. Acreage was allotted to the six representative <br />river reaches. <br /> <br />The Blaney-Criddle empirical formula for estimating plant evapotranspiration was chosen for this study. <br />The weather station at Fort Lewis College in Durango was utilized for historic climatological data. The <br />average annual net consumptive use factors employed for the three vegetation groups were - trees (5.5 <br />acre-feet/year), brush (5.5 acre-feet/year), and herbaceous cover (1.5 acre-feet/yeari. <br /> <br />The following table depicts the results of the consumptive use analysis. <br /> <br />La Plata River Consumptive Use Analysis <br /> <br /> Elevation Tree Tree Brush Brush Herbaceous Herbaceous Total cu <br />Reach Acres ab MSL (ft.) Density % CU Density % cu Density % cu Acre- feet/yr. <br />1 302 6200-6480 5 83.1 40 664.4 40 181.2 928.7 <br />2 166 6480-6880 10 91.3 25 228.3 30 74.7 394.3 <br />3 297 6880-7280 15 245.0 20 326.7 60 267.3 839.0 <br />4 169 7280-7600 15 139.4 20 185.9 40 101.4 426.7 <br />5 128 7600-7840 15 105.6 10 70.4 40 76.8 252.8 <br />6 106 7840-8080 15 87.5 25 145.8 40 63.6 296.8 <br />Totals 1168 3138.3 <br /> <br />The annual consumptive use of water for phreatophytes in this study area is dependent upon the depth to <br />water table, which fluctuates in both season and distance from the river channel. Therefore, the <br />consumptive use assignments for the three vegetative groups retain a.:!: 10% margin of error. Including <br />other potential inaccuracies in the percentage or density of cover and acreage calculations, the total <br />estimated consumptive use carries and accuracy of::!:: 20 % or 637 acre-feet/year. <br /> <br />2 <br />