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<br />Parameters of the Green-Ampt equation can be estimated either by calibration or <br />from information available from soil survey data. Methods have been developed by to <br />determine parameters from laberatory measurements of water content, soil porosity, <br />residual saturation, bubbling pressure, and pore size. In lieu of detailed measurements, <br />the following parameter estimates can be used based on soil texture classes: <br /> <br />Table 7.6 <br /> <br /> GREEN-AMPT PARAMETERS <br /> TOTAL POROSITY WETTED FRONT HYDRAULIC <br />SOIL TYPE SUCTION CONDUCTIVITY <br /> P wf(in) k (inlhr) <br />Sand 0.437 1.95 4.135 <br />Loamy Sand 0.437 2.41 1.205 <br />Sandy Loam 0.453 4.33 0.510 <br />Loam 0.463 3.50 0.260 <br />Silt Loam 0.501 6.57 0.135 <br />Sandy Loam Clay 0.398 8.60 0.085 <br />Clay Loam 0.464 8.22 0.046 <br />Silty Clay Loam 0.471 10.75 0.033 <br />Sandy Clay 0.430 9.41 0.025 <br />Silty Clay 0.479 11.50 0.018 <br />Clay 0.475 12.45 0.012 <br /> <br />It should be noted that for totally dry initial conditions, total porosity minus water <br />content is equal to effective porosity, which is generally abeut 75 to 97 percent of the total <br />porosity. <br /> <br />7. FIELD MEASUREMENT OF INFILTRAiION. <br /> <br />A~hough many methods can and have been used to measure infiltration rates in <br />the field, a common practice is through the use of a double ring infiitrometer. These <br />consist of concentric cylinders approximately 40 cm high. Diameter of the inner ring is 28- <br />33 cm, while the outer ring is 50-60 cm ill diameter. Concentric rings are used, with <br />measurement confined to the inner ring, in order to minimize error due to flow divergence <br />in directions other than the vertical. In the field, the cylinders are driven into the soil <br />surface to approximately 15 cm of depth. Water is filled to a depth of about 10 cm in beth <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />DRAFT <br /> <br />7.26 <br />