Evaluating the Role of Flooding in a Southwestern Riparian System

Abstract

Although riparian system researchers intuitively understand the general role of flooding in these plant communities, very little quantitative analysis or physical modelling of these flooding effects has been undertaken. This paper describes a methodology for analyzing flood influences by utilizing vegetation monitoring along river transects and a sophisticated flood hydraulics computer model (HEC 2). The project is addressing important questions such as "What magnitude of foods will alter the physical structure and species composition of the plant community? Are major floods essential in creating open floodplain areas wherein regeneration of riparian plants can take place? How does flood timing during the growing season affect the germination of seeds and survival of seedlings?" The flood hydraulics study described herein provides an analysis method that is readily transferrable to other riparian systems, and anticipated results may offer some quantification of flooding characteristics which translate to any system composed of similar plant species. For instance. if mortality thresholds of such physical forces as flow velocity. depth. tractive shear stress, and stream power can be identified for selected riparian species, such information may be quite valuable to those engaged in restoration of disturbed systems. in specifying reservoir releases needed to maintain riparian vegetation downstream of dams, and in instream flow protection efforts seeking to protect essential environmental processes which sustain natural riparian systems.