QUANTIFYING AND DELINEATING SPATIAL VARIATIONS OF SURFACE INFILTRATION IN A SMALL WATERSHED

The focus of this project is to determine which data collection techni ques are best suited for quantifying and delineating spatial variation s in surface infiltration and for estimating infiltration parameters u sed in computer models for simulation of runoff quantity following sum mer rainstorm events from a small watershed (Incline Creek watershed, Nevada) in the Lake Tahoe Basin. Field tests which give the infiltrati on parameters of sorptivity and hydraulic conductivity, two parameters found in the Philip infiltration model, were performed in the watersh ed using a disk permeameter. These held data were combined with covera ges in an existing Geographical Information System (GIS) database and held observations of surface attributes (soil type and vegetation) whi ch are known to contribute to variation in infiltration rates. Statist ical tests performed on the held-test data indicate that the only surf ace attribute which influences variations in infiltration rates in thi s watershed (owing mainly to limited variations in soil type) is veget ation. Further, time-to-pending calculations which indicate when and i f runoff might occur following the start of a precipitation event indi cate that for most precipitation events likely to occur in this area d uring the summer, infiltration in all but nonforested areas is unlikel y. The coverages in the GIS database were used to develop a map of the watershed which delineates areas of low potential infiltration from a reas of high potential infiltration which can be used in parameter est imation and watershed conceptualization in computer modeling of runoff .