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(elevations) because of changes in meteorologic conditions. Flood- plain management, including the design of a flood-warning system needs an accurate assessment of the magnitude and frequency of flooding. The concentration of population along these foothill streams, coupled with the nature of flash floods, dictates sound scientific methods be employed in flood-plain management (including flood-warning systems). Consequently flood-plain management seeks an optimal balance of identifying the true flood potential. PALEOFLOOD TECHNIQUES Because of the relatively few floods in the streamflow records in the foothills in this area, conventional hydrologic analyses does not provide the most accurate assessment of the magnitude and frequency of floods. Paleohydrologic studies can assess the magnitude and frequency of flooding and can be used to enhance conventional hydrologic techniques. Paleoflood hydrology is the study of the movement of water and sediment in channels. Historic and prehistoric floods in streams are recorded as distinctive deposits and landforms in and along channels. The interpretation of these deposits and landforms provides supplemental information about the spatial occurrence, magnitude, and frequency of large floods. Large floods leave diatinctive erosional and depositional features that remain in the channel until a larger flood reworks the deposits. These features are easily recognizable and long lasting (mul t i -thousands of years). In this type of study, lack of flood evidence is as relevant as tangible flood evidence (it indicates that floods above a given magnitude have not occurred for many thousands of years) . A brief overview of paleohydrologic techniques used in the onsite investigations follows. Intense rain causes rill and gully erosion on steep unvegetated surface. Occurrence or lack of occurrence of rills and gullies is indicative of whether intense rain occurs. During a flood the fluid stress exceeds a critical value which results in streambed and bank erosion. The greater the fluid stress the more material eroded and the higher the rate of sediment transport. It has been shown (Jarrett, 1987) that for steep, small, tributary basins such as those in this study area, streamflow greater than about 20~ to 300 cubic feet per second will leave easily recognizable flood features in channels. This range in streamflow is termed the erosion threshold discharge. Following floods erosional features include scarred and raw banks and channels often removing much of the vegatation (Figure 2A). Uprooted trees or debris-scarred trees and bushes are located in the floodplain. Flood debris is very common and is lodged along the stream bank and upstream from obstructions, such as trees and boulders (in Colorado's semiarid climate this flood debris remains for 50 to 100 years). Steep mountain channels subject to floods typically are scoured to bedrock and take many hundreds to thousands of years to recover to preflood condi tions. During boulders in a flood moss and lichen are abraided from the bedrock and the channels up to the level of the flood. The regrowth 4.