Laserfiche WebLink
<br />To allow for flow from impervious areas into pervious areas, the <br />impervious area of residential zones was reduced to 65 percent of the <br />total; no reduction was made for nonresidential zones. The basic as- <br />sumptions were: (1) That an average of 65 percent of the rainfall in <br />residential zones becomes direct runoff in the drainage system, and (2) <br />that 100 percent of the flow from nonresidential zones reaches the <br />drainage system by direct sewering. <br /> <br />Rainfall and Runoff <br /> <br />Peak discharges were meas~red at four continuous-record gaging <br />stations and 10 crest-stage partial-record stations. Figure 3 shows <br />the locations of the stream-gaging stations. Table 4 gives an identi- <br />fying map number, basin name, type of station, and availability of <br />streamflow records. <br /> <br />Rainfall amounts and inteasities were recorded at rain gages <br />throughout the area. The locations and designation of the rain gages <br />are shown on figure 3; table 4 shows the availability of rainfall rec- <br />ords. Table 5 shows the grouping of rain gages and the rainfall-weighting <br />methods used. <br /> <br />Evaporation <br /> <br />Daily evaporation was used to compute daily potential evapotran- <br />spiration, which in conjunction with soil moisture, controls the rate of <br />infiltration and ultimately the amount of rainfall excess that appears <br />as surface runoff. <br /> <br />Monthly sunken-pan evaporation records since January 1917 were avail- <br />able from the Texas Agricultural Experiment Station near Denton, which is <br />30 miles (48.3 kilometers) northwest of Love Field in Dallas. Weather <br />Bureau Class A pan records were available since mid-1953 for another evapo- <br />ration station located at Grapevine Dam, 18 miles (29.0 kilometers) south <br />of Denton and 14 miles (22.5 kilometers) northwest of Love Field. <br /> <br />For the period of study prior to 1953 (except 1914-16), daily pan <br />evaporation was estimated from monthly records for the Denton station. <br />Daily evaporation for this period was estimated by dividing monthly evapo- <br />ration by the number of days in each month. For the period 1914-16, prior <br />to the availability of any evaporation data, the average monthly evapo- <br />ration for the period 1917-53 was used to estimate daily evaporation. <br />After 1953, observed daily pan evaporation at the Grapevine Dam station <br />was' used. <br /> <br />-13- <br />