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08/8/00 <br />WATER FEATURES <br />1 Endnote -- DATER FEATURES <br />I This report gives estimates of various soil water features. The estimates are used in land use planning that involves <br />engineering considerations. <br />Hydrologic soil groups are used to estimate runoff from precipitation. Soils not protected by vegetation are <br />assigned to one of four groups: They are grouped according to the infiltration of water when the soils are thoroughly <br />wet and receive precipitation from Long-duration storms. The four hydrologic soil groups ere: <br />Group " A". Soils having a high infiltration rate (low <br />runoff potential) when thoroughly wet. These consist mainly <br />of deep, well drained to excessively drained sands or <br />gravelly sands. These soils have a high rate of water <br />transmission. <br />G raup "B". Soils having a moderate infiltration rate when <br />thoroughly wet. These consist chiefly of moderately deep or <br />deep, moderately well drained or wets drained soils that <br />have moderately fine texture to moderately coarse texture. <br />These soils have a moderate rate of water transmission. <br />Group "C". Soils having a slow infiltration rate when <br />thoroughly wet. These consist chiefly of soils having a <br />layer that impedes the downward movement of water or soils <br />of moderately fine texture or fine texture. These soils <br />have a slow rate of water transmission. <br />Group "D". Soils having a very slow infiltration rate (high <br />runoff potential) when thoroughly wet. These consist <br />chiefly of clays that have a high shrink-swell potential, <br />soils that have a permanent high water table, soils that <br />have a claypan or clay layer at or near the surface, and <br />soils that are shallow over nearly impervious material. <br />these soils have a very slow rate of water transmission. <br />If a soil is assigned to two hydrologic groups in this report, the first letter is for drained areas and the second <br />is for undrafned areas. Flooding, the temporary inundation of an area, is caused by overflowing streams, by runoff from <br />adjacent slopes, or by tides. Water standing for short periods after rainfall or snowmelt is not considered <br />flooding, nor is water in swamps and marshes. This report 9i vas the frequency and duration of flooding and <br />the time of year when flooding is most likely. Frequency, duration, end probable dates of occurrence are estimated. <br />Frequency is expressed as "None", "Rare", "Occasional", and "Frequent". "None" means that flooding is not probable; <br />"Rare" that it is unlikely but possible under unusual weather conditions; "Occasional" that it occurs, on the <br />average, once or less in 2 years; end "Frequent" that it occurs, on the average, more than once in 2 years. <br />Duration is expressed as "Very brief" it less than 2 days, "Brief" if 2 to 7 days, "Long" it 7 to 30 days, and "Very <br />for if more then 30 days. The information is based on evf dente in the soil profile, namely thin strata of gravel, <br />sar,,, silt, or clay deposited by floodwater; irregular decrease in organic matter content with increasing depth; <br />and absence of distinctive horizons that form in soils that are not subject to flooding. Also considered are local <br />information about the extent and levels of flooding and the relation of each soil on the landscape to historic floods. <br />