Laserfiche WebLink
<br />There are many limitations to the use of the Green-Ampt equation in actual <br />field conditions. For example, hydraulic conductivity, as well as other soi1- <br />water properties, is highly variable in space because of the heterogeneity of <br />natural soils (Nielson and others, 1973). The parameters KSAT and P are, there- <br />fore, essentially empirical indices that must be found by experiment. The model <br />is best suited to uniform, coarse-textured soil profiles where the wetting front <br />is sharp and complications from surface crusting and air entrapment are absent. <br />At best, it offers a frame of reference from which to evaluate the similarities <br />and dissimilarities of both sprinkler-induced runoff and naturally occurring <br />runoff events. <br /> <br />Overland-Flow Routing <br /> <br />Surface runoff is computed by using the kinematic-wave approximation to <br />overland flow. The partial differential equation to be solved for the uni- <br />formly sloping, overland-flow plane is: <br /> <br />ah + h = di <br />at ax r - dt; <br /> <br />(4) <br /> <br />where <br /> <br />h = the depth of flow, ft; <br /> <br />t = time, s; <br /> <br /> <br />q = the rate of flow per unit width, ft3/s/ft; <br /> <br /> <br />x = distance down plane, ft; <br /> <br /> <br />r = the rainfall rate, ft/s; and <br /> <br />di _ <br />dt - the infiltration rate, ft/s. <br /> <br />The relation between hand q for the kinematic wave is: <br />q = ahm; <br /> <br />(5) <br /> <br />where a and m are functions of overland-flow-plane characteristics. <br />turbulent flow condition: <br /> <br />Assuming <br /> <br />_ 1.49 S~. <br />a - FRIC ' <br /> <br />(6) <br /> <br />and <br /> <br />m = 1.67; <br /> <br />(7) <br /> <br />where <br /> <br />10 <br />