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<br />Parameters of the (ireen-Ampt equation can be estimatlJd either by cal bration or <br />from information available from soil survey e1ata. MettlOds have been developeel by to <br />determine parameters from laboratory measurements of water content. soil porcsily. <br />residual saturation, bubblin(l pressure, and po'e size. In lieu of detailed meaSLJre'11nnts. <br />the following parameter estimates can be usnd based on soil texture classes: <br /> <br />Table 7.6 <br /> <br /> GREEN-AMPT F- <br /> TOTAL POROSITY r <br />SOIL TYPE <br /> P <br />Sand 0.437 <br /> ~- <br />Loamy Sand 0.437 <br />Sandy Loam 0.453 <br />Loam 0.463 <br />Silt Loam 0501 <br />Sandy Loam Clay 0.398 <br />Clay Loam 0.464 <br />Silty Clay Loam 0.471 <br />Sandy Clay 0.430 <br />Silty Clay 0479 <br />Clay 0.475 <br /> <br />..------..------ <br />...-.----.--------- <br /> <br />AI1AMETERS <br /> <br />--------.-.r:--------- <br />WETTED FRONT HYDRA,Ul.JC <br />SUCTION CONDUCTIVITY <br />wf(in) k (inlhr) <br />- - . - - <br />... - . ---.-- <br /> <br />< 95 4.1:l5 <br /> <br />2.41 1.2CS <br /> <br />4.33 0.5'0 <br /> <br />3.50 0.260 <br /> <br />6.57 O. D5 <br /> <br />860 <br /> <br />0085 <br /> <br />822 <br /> <br />0.046 <br /> <br />1075 <br /> <br />0033 <br /> <br />9.41 <br /> <br />0.Q25 <br /> <br />11.50 <br /> <br />0.018 <br /> <br />12.45 <br /> <br />0012 <br /> <br />It should be noted t11at for totally dry initial conditions. total porosity minus water <br />content is equal to effective porosity, which is generally about 7S to 97 percent of the talal <br />porosity. <br /> <br />7. FIELD MEASUREMENT OF INFILTRATION. <br /> <br />Although many mettlOds can and have been used to measure infiltration rates in <br />the field, a common practice is through the lIse 01 a double rin(j infiltrometer. Trese <br />consist of concentric cylinders approximately 40 cm high Diameter of the inner ring is 213.. <br />33 cm, while the outer ring is 50-60 cm in diameter. Cc ncentric rings are useel. with <br />measurement confined to the inner ring, in oreler to rninimiz,g error due to flow divergence <br />in directions other than the vertical. In the field, tile cylinders are driven into the soil <br />surface to approximately 15 em of depth. Water is filled to a depth of about 10 cm in Ilcth <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />DRAFT <br /> <br />7.26 <br />