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<br />. <br /> <br />. <br /> <br />. <br /> <br /> TABLE 5 <br /> PERCENT IMPERVIOUS <br />LAND USE PERCENT IMPERVIOUS <br />Low-Density Residential 20- 30 <br />Medium-Density Residential 25 - 35 <br />High-Density Residential 30-40 ?;{ - b ~ <br />Business - Commercial 40-90 i1O""lO <br />Light Industrial 45 - 65 r;o - '"]0 <br />Heavy Industrial 50-70 '0 -l!:' <br /> <br />Frequency Rainfall <br /> <br />The Albuquerque District generated point rainfall for the 50.0%-, 20.0%-, 10.0%-,4.0%-, <br />2.0%-, and 1.0%-chance storms based on NOAA Atlas 2, Precipitation-Frequency Atlas of the <br />Western United States, Volume III-Colorado (1973). The 0.2%-chance rainfall was extrapolated <br />from a graphical plot of the other frequency amounts. <br />Both the Oak Creek and Coal Creek watersheds are elongated and exhibit irregular shape. To <br />compute the percent of areal reduction to apply to the point rainfall, the Albuquerque District <br />centered an elliptical rainfall cell over each watershed. The axes for each elliptical cell varied and <br />were established to ensure that the entire watershed was incorporated within the cell. The <br />Albuquerque District reduced the point rainfall in accordance with the NOAA Atlas depth-area- <br />duration curves to equal the area of the appropriate elliptical cell. The areally reduced rainfall was <br />applied uniformly to each watershed. Depth-area reduction for Coal Creek was based on an elliptical <br />cell measuring approximately 35 square miles. For Oak Creek, an elliptical cell with an area of <br />approximately 160 square miles was used. The 50.0%-, 20.0%-, 10.0%-,4.0%-,2.0%-, 1.0%-, and <br />O.2%-chance rainfall for the Oak Creek and Coal Creek watersheds are listed in Table 6. <br /> <br /> TABLE 6 <br /> FREQUENCY RAINFALL <br /> 50.0%- 20.0%- 10.0%- 4.0%- 2.0%- 1.0%- 0.20%- <br /> Chance Chance Chance Chance Chance Chance Chance <br /> Flood Flood Flood Flood Flood Flood Flood <br /> (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) <br />Coal Creek 1.87 2.45 2.84 3.46 3.75 4.23 5.05 <br />Oak Creek 1.79 2.35 2.80 3.32 3.60 4.06 4.75 <br /> <br />8 <br />