important consideration in site selection. A vast majority of Candidate Sites are on plains with low mountains. They are typically located in lowland valleys or plains bordering more rugged terrain (Black and Veatch 1977). Thus many Candidate Sites will probably be gently sloping bajadas (alluvial fans), characterized by a desert "pavement" surface, a dendritic pattern of small ephemeral washes, and moderate to widely spaced desert scrub vegetation. Shreve (1934) outlines factors which determine amount of runoff, the most important being: (1) intensity of rainfall, (2) degree of slope, (3) texture of the soil, (4) nature and density of the vegetation, (5) amount of litter or stones on the surface, and (6) moisture of the soil surface. Due to a combination of infrequent, high intensity rainfall events, presence of sparse perennial vegetation, and presence of a desert pavement surface, desert bajadas tend to have high runoff rates compared to other geomorphic surfaces, and moister regions (Shreve 1934). High runoff in the desert is also accompanied by increased erosion rates. Some of the above factors will be influenced by soil compaction and above-ground destruction. Compaction, by increasing bulk density of the soil, will have an inhibitory effect on infiltration rate similar to that caused by a change in soil texture. Infiltration rate is known to increase with particle size increase (Fireman 1944), especially in arid regions (Evenari st at. 1971). If substantial areas of the desert are cleared and graded, runoff will greatly increase. A cover of dead and/or living vegetation usually increases infiltration in arid zones (Tadmor and Shanan 1969) by reducing rain impact or through some physical or chemical modification of the soil surface (Lyford and Qashu 1969). To minimize erosion of the soils beneath collector fields, as much area as possible should be left undisturbed. An important consideration when discussing erosion of desert areas is the common occurrence of a desert pavement surface . A desert pavement tends to form on desert bajadas due to loss of finer soil particles in runoff water, resulting in a stony cemented surface layer. Although it
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