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e < . CODE I since the policy of no new development occurring at elevations below the 100- year event is in effect. The table shows a large increase in expected annual damages. This increase is because (1) damage does occur for new basement construction, (2) the 100- year flood for 1990 land use conditions is higher than the 100-year flood for existing land use conditions, and (3) damages are sustained by new development from events that exceed the lOO-year event. Several other evaluations that include a number of alternative control and flood proofing policies are included to demonstrate the broad capability of the spatial data management technique as well as present some interesting evaluations of policies designed to manage flood losses. The capabilities of the technique for evaluating a range of nonstructural floodplain management measures is described by (Webb and Burnham, 1976). TABLE 4. Selected Damage Assessments, Trail Crcek. (Expected Annual Damage in 1000's $) EV ALVA TlON CONDITION DAMAGE REACH Code land Use Policy. Hydrology 2 3 Total Existing (1974) 1.5 1.9 11.9 15.3 Existing e X 1990 with no development controls 1990 1033.3 350.0 32.7 1416.0 IV 1990 with new development at 1990 19.3 63.8 23.8 ]06.9 at 1975 I GO-year flood level V 1990 w/new devel. (IV 1975 100- 1990 ]6.8 18.9 4.7 40.4 yeu and flood proofed to ground floor VlIl 1990 w Jnew devel. @ ) 990 ) 00- 1990 ] 1.9 16.0 2.8 30.7 year and flood proofed to ground Ooor *The ) 990 land use condition is a projection based on local agency judgment. In some instances. such as Damage Reach No.3, 1990 urban type development has displaced some present agricultural de- velopment. ENVIRONMENTAL ASSESSMENT . , The objective of the environmental assessment is to provide a general description of the environmental status of the watershed areas for alternative land use patterns. The ap- proach taken was to confine the analysis to specific achievable and quantifiable assess- ments and includes coincident tabulation, locational attractiveness analysis, urban storm water water quality and land surface erosion analysis, and simulation of the dynamic quality response of receiving water to urban storm water runoff and dry weather sani- tary luading. The techniques draw heavily upon the grid cell data file for parameter definition, and on spatial analysis techniques for some computations. . e 13