Erosion Risk Analysis for a Southwestern Arroyo

A procedure is outlined for establishing a flooding and erosion buffer zone along an arroyo. The approach is applicable in general to ephemeral stream systems of the Southwest, while the hydrologically based definition of erosion and flood risk is applicable specifically in an urban setting. The risk analysis recognizes both the short-term impacts of flooding and erosion and the cumulative impacts of erosion over the long term. The procedure is based on an understanding of the basic physical processes of an arroyo system and integrates simple qualitative concepts with quantitative analysis of the vertical dynamics of the arroyo bed. Trends in vertical instability such as aggradation and degradation are then extended in the horizontal dimension to provide estimates of lateral erosion and channel migration potential. Application of the procedure to Calabacillas Arroyo northwest of Albuquerque, New Mexico, demonstrates reasonable results considering the documented dynamic behavior of ephemeral stream channels in the Southwest. The procedure answers a current need for engineering analysis techniques to support management and control of arroyos in an urban setting.