EThomework3

EThomework3 - Intro to Hydrogeology Homework 3 Due: Feb. 3,...

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Unformatted text preview: Intro to Hydrogeology Homework 3 Due: Feb. 3, 2012 Evapotranspiration and runoff A. The average monthly air temperature in F0 for Miami is given in the table below. Using the Thronthwaite method and the attached tables estimate the potential evapotranspiration for each month. Averae Monthl air temperature F0) in Miami 77.0 79.2 83.5 85.6 90.4 87. La. Provide the monthly ET values in cm/month and in inches/month in a table (preferably in Excel). 1.'o. Sum the monthly values to estimate the annual potential ET (cm/year and inches/year) and include on the table. 10. The following table has the average monthly precipitation (in inches) at Miami Airport. Za. Plot on a graph (preferably in Excel) the monthly Potential ET you calculated in problem 1 in inches per month in one black and the average monthly rainfall in inches per month in grey on the same graph. 2b. Mark the areas on the graph were you would expect a gain of water storage in Miami and areas that you would expect a loss in water Storage. 59 EXAMPLE 2.2 the potential evapotranspiration from an area. The Thornthwaite equation (see Gray et a]: 1970) is: 10T' a E = a! ‘. r 1.62( I ) (2.4) 12 1.5 T . I = J2 i=1 ( 5 ) a = 0.492 + 0.01791 — 0. 0000771!2 + 0. 00000067513 (2.6) ., ..,,,[,, 2.22721 . . . 1 a "I: where E;- is the potential evapotranspiration in cm/rnonth, Ta,- is the mean monthly air temperature in 0’ for month i, I is the annual heat index, and a is constant. It is assumed that each day has 12 hours of sunshine with 30 days in a month. Table 2.3 lists the correction factors to adjust the hours of sunshine in each day for various latitudes. Temperature may also be in F°(C° = [P - 32}_x 5/9, or F° = C° x 9/5 + 32). The second column of Table 2.4 lists the monthly temperatures between April and October in (from Gray et a]_, 1970) 1961 at Saskatoon, Canada. Calculate the potential evapotranspiration for an alfalfa crop using the Thornthwaite method. SOLUTION Temperature needs to be converted from F ° to c1. Next, the heat index is calculated using Eq. (2.5). Each term is calculated and listed in the fourth column of Table 2.4. The heat index is the summation of all the terms. 12 T_ 1.5 I=Z(?m-) =0.21.+3.56+7.92+7.68+8.90+2.32+0.89=31.48 i=1 TABLE 2.3 NRC mean hours of bright sunshine expressed in units of 30 days of 12 hours each day North Lat. J F M - A M J J A S O N D 0 r N 1.04 0.94 1.04 1.01 1.04 1.01 1.04 1.04 1.01 1.04 1.01 1.04 10 1.00 0.91 1.03 1.03 1.08 1.06 1.08 1.07 1.02 1.02 0.98 0.99 %0 0.95 0. 90 1.03 1.05 1.13 1.11 1.14 1.11 1.02 1.00 0.93 0.94 0 0.90 0.87 1.03 1.08 1.18 1.17 1.20 1.14 1.03 0.98 0.89 0.88 35 0.87 0.85 1.03 1.09 1.21 1.21 1.23 1.16 1.03 0.97 0.86 0. 85 4011'. 0.84 0.83 1.03 1.11 1.24 1.25 1.27 1.18 1.04 0.96 0.83 0.81 45 0.80 0.81 1.02 1.13 1.28 1.29 1.31 1.21 1.04 0. 94 0.79 0.75 50 0.74 0.78 1.02 1.15 1.33 1.36 1.37 1.25 1.06 0.92 0.76 0.70 Source: Gray et.aI., 1970. Handbook on the principles of hydrology. Reprinted by permission of the National Research Council of Canada. ...
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EThomework3 - Intro to Hydrogeology Homework 3 Due: Feb. 3,...

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