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U. S. DEPARTMENT DF AGRICULTURE PAGE t OF 3 <br />NAiUkAL~REsOURLES CONBERVATION SERVILE ~ • Od/21i5d <br />RATER FEATURES <br />Endnote -- PATER FEATURES <br />This report gives estimates of various soil eater features. The estimates ere used in land use planning that involves <br />engineer ing COnslderatl0ns. <br />HYdr01091C 5011 9roUp5 are Used t0 estimate runoff from DreClDltatl0n, JO115 npt pfoteCted by vegetation are <br />assigned to one of four groups. They are grouped ectording to the infiltration of eater vhen the soils are thoroughly <br />wet and receive precipitation from long-duration storms. The four hydrologic soil groups are: <br />Group ~ A'. foils having a high infiltration rate (lov <br />runoff potential) vhen thoroughly wet. These consist mainly <br />of deep, cell drained to escessivelr drained sends or <br />gravelly sands. These soils have a high rate of voter <br />transmission. <br />Group 'B'. Soils having a moderate infiltration rate vhen <br />thoroughly wet. These consist chiefly of moderately deep or <br />deep, modereteir veil drained ar veil drained soils that <br />have moderately tine texture to moderately coarse tetture. <br />These soils have a moderate rate of eater transmission. <br />Group 'C'. soils having a sloe infiltration rate vhen <br />thoroughly vet. These consist chiefly of soils having a <br />layer that impedes the dovnuard movement of wafer or soils <br />of moderately fine tetture or fine texture. These soils <br />have a slov rate of eater transmission. <br />Group 'D'. Soils having a very sloe infiltration rate (high <br />runoff potential) vhen thoroughly wet. These consist <br />chiefly of clays that have a high shrink-swell potential, <br />soils that have a permanent nigh voter table, soils that <br />have a cl9ypen or clay layer at or near the surface, and <br />soils that are shallow over nearly impervious materiel. <br />these soils have a very slov rate of eater transmission. <br />if a soil is assigned to two hydra Logic groups in this report, the first letter is for drained areas and the second <br />is for undrained areas. Flooding, the temporary inundation o} en area, is caused by overflowing streams, by runoff from <br />adjacent slopes, or br tides. Peter standing for short periods after rainfall or snoumelt is not considered <br />flooding, nor is eater in swamps and marshes. This report gives the frequency end duration of flooding and <br />the time of year vhen flooding is most likely. Frequency, duration, end probable dates of occurrence are estimated. <br />Frequency is etDressed es 'None', 'kere', 'Occasional', end '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 i rears; and 'Frequent' that it occurs, on the average, more than once in 2 rears. <br />Duration is etpressed es 'Very brief' it less than 2 days, 'Brief' if 't to 7 days, 'Long' if 7 to 3D days, end 'Very <br />long' if mare than 30 days, the information is based on evidence in the soil profile, namely thin strata of gravel, <br />sand, 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 end levels of flooding and the relation of each soli on the landscape to historic floods. <br />