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N 1-4 o W that 468 square miles of Mancos Shale are exposed in the Price River Basin. Extrapo- lating by the ratio of these areas (8 factor of 21.8) gives the loadings on Table 6.6. Ponce (1975,) estimated the average annual salt load at Woodside as 3.68 x 108 kg. As found by Ponce (1975) and White (1977a), the extrapolated model results, when compared with the total salt load, suggest that the salt loads from overland flow and natural channels are a small portion of the total. These results are believed to be reasonably representative of long periods of time. The overland flow salt load is dependent upon the variables (precipitation intensity and peak runoff rate) of Equation 5.6. The channel salt load is directly proportional to the salt loading coefficient of Equation 4.5 and is sensitive to the routing coefficients and channel character- istics applied in the model. None of these inputs change drastically from year to year. Because the amount of salt pickup varies considerably with the type of Mancos Shale over which the runoff passes., an attempt was made to refine the estimates of Table 6.6 by taking into account the different types of exposed shale within the valley floor area. For simplicity and because they supply most Table 6.6. Extrapolated annual salt load at Woodside. Source Annual Salt Load Overland Flow 1st Order Channels 2nd Order Channels 3rd Order Channels 4th Order'Channels kg 2.11 x 107 2.74 x 106 1.32 x 106 8.61 x 105 3,42 x 105 23,250 3,000 1,450 950 375 Tons ----------------------------------------------------- Totals 2.64 x 107 29,025 of the salt loading to surface runoff (Table 6.6), only overland and mi crochannel flows were included in this analysis. Furthermore, the following simple relationship was adopted as the microchannel salt loading function. y - a xb . . .'. . . . . . . . . . (6.1) in which y x The mass of salt pickup The accumulated runoff volume for a particular event Co.nstants for a particular shale type a and b Values of a and b in Equation 6.1 were developed for the six Mancos Shale'soils. Data obtained 100 feet downstream in micro- channel studies conducted by White (1977) in various shale types (Figure 6.4) were used to estimate accumulated salt mass for various accumulated flows (Table 6.7). These reults were used to estimate the values for a and b given in Table 6.8. In order to apply Equation 6.1 to the various areas of shale within the basin, Figure 5.8 was used to estimate an average microchannel length and order for each shale type for each area included in the analysis. To adjust the salt loading estimates of Equation 6.1 for channel lengths other than 100 feet, data from Table 6.7 were used. For each shale type, salt loading was found to vary with channel length to the 0.4 power (Figure 6.5). Subroutines RAIN and HYDRGY (Chapter V) were coupled to the appropriate relationship by shale type for overland flow (adjusted by data from Table 5,2) and microchannel flow (adjusted by data from Table 6.9 and by Figure 6.5). The resulting model (listed in Appendix E, Table E.3) was operated over a 3-year period. The results, summarized by Table 6.9, suggest that the division of the salt contribution between microchannel and overland flow processes is extremely variable Table 6.7. Accumulated salt mass vs. accumulated flow for various shale types (from White 1977). Accumulated Flow Accumulated Salt Mass at IOo-Foot Station (gms) of Water at 100-Foot Station Undivided Upper Blue Middle Blue Lower Blue Tununk Masuk (ft3) Shale Gate Shale Gate Shale Gate Shale Shale Shale 0 0 0 0 0 0 0 10 105 320 400 10 7 12 20 195 575 700 17 12 20 30 265 870 950 32 20 27 50 385 1355 1350 44 27 40 100 685 2200 2400 58 50 80 200 1335 3045 3500 96 88 132 300 1540 3950 3900 110 400 1670 4900 120 600 1955 800 2120 61