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l_- (FIRST DRAFl' - SUBJECT TO CHANGE) Moderately slow Moderate Moderately rapid Rapid Very rapid 0.2-0.6 0.6-2.0 2.0-6.0 6.0-20 More than 20 Values listed are estimates of the range in rate and time it takes for downward movement of water in the ,major soil layers when naturated, but allowed to drain freely. The estimates are based on' soil texture, soil structure, available data on permeability and infiltration tests, and drainage ,observations of the water movement through soils. In most cases, particularly with soil horizons that are high in clay or organic matter, permeability rates 'under unsaturated conditions are considerably higher than the values given here. On a given soil type, percolation through the surface layer varies according to land use and management as well as with initial moisture content. Depth to seas.onal water table. Depth of upper surface of ground water or depth below which soil is saturated with water. Great variation may be expected where the depth to water table is shown as greater than 60 inches. It may_ range from depths of 5 to 10 feet to depths of several hundred feet. Flood hazard. by water from from adjacent as follows: Susceptibility to a temporary covering of the, soil surface sources such as streams overflowing their banks or runoff or surrounding slopes. Flood frequency classes are defined None: Rar'e: No reasonable possibility of flooding. Flooding unlikely but possible under abnormal conditions. No evidence of flooding within the soil profile. Pedogenic horizons usually have developed. (Flooding probability is so low that it imposes no more than slight or moderate soil limitation ratings' for soil uses except those with high per-acre investments,' such as residential developments). Common: Flooding likely under normal~onditions. The soil profile ,shows evidence of flooding., (The probability of recurring floods is great enough to impose severe limitations on many uses of soils such as sanitary facilities and community development. Restrictions on farming may be slight to severe-depending on duration and season of floOding. Shrink-sWell potential. Soil quality that determines its volume change with change in moisture content. Building foundations, roads and other structures may be severely damaged by the shrinking and swelling of soil. The volume change of soU is influenced by the amount of moisture change and the amount and kind of clay.' . ' Classes used to express shrink-swell behavior in terms Of ,coefficient .of linear extehliibility (COLE) are:, '_, Low Moderate High < 0.03 COLE 0.03-0.06 COLE >0.06 OOLE ( 2)