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<br />Table 2.--Variability and accuracy of statistical characteristics of streamflow. <br />Streamflow characteristics Variability Standard error. In percent, <br /> index2 for indicated length of record <br /> Yea rs <br /> 5 10 25 50 100 <br />Mean annual flow 0.418 44 30 20 14 10 <br />Standard deviation of annual flow 35 25 15 I) 8 <br />Mean monthly flow (average) .673 75 50 32 22 16 <br />Standard deviation of monthly flow 35 25 15 11 8 <br />50-year peak flow .433 87 58 36 24 18 <br />50-year 7-day high flow .458 93 62 38 27 19 <br />2-year 7-day low flow .692 78 53 32 23 16 <br />20-year 7-day low flow .692 110 73 43 30 21 <br /> <br />from manmade changes. One or two stations should be located In each major <br />drainage area In the State, and the stations should gage streams having <br />differing physical characteristics. <br /> <br />Environmental Data <br /> <br />The goal for this type of data is to provide information related to <br />the hydrologic environment of the basin and stream channel as follows: <br /> <br />1. Stream channel geometry including widths, depths, slopes, <br />hydraulic roughness, bars and berms, and description of bed and <br />bank material. <br /> <br />2. Profiles at flood elevations and areas subject to inundation by <br />floods. <br /> <br />3. Data on land use including Irrigated acreage, water storage, urban <br />areas, cultivated acreage, and forested acreage. <br /> <br />4. Time of travel of water and waste in channels. <br /> <br />5. Data on location, extent, and characteristics of aquifers that <br />are hydraulically connected to stream channels. <br /> <br />6. Basin characteristics: area, shape, land and stream slopes, and <br />soi 1 s. <br /> <br />7. Climatic characteristics. <br /> <br />2Average for the State. <br /> <br />16 <br />