Identification of river channel change to due to urbanization

Abstract

Techniques for determining the precise location of river channel changes are required to complement space-time substitution and three major techniques are illustrated for the Monks Brook drainage basin in central southern England. First, channel widths were measured from large-scale topographic maps of three dates, the results compared with field measurements, and the spatial pattern of planform change was constructed. Secondly, field indicators based on vegetation, structures and morphological criteria were used to quantify channel width, depth and capacity changes at particular locations. Thirdly, mapping of the spatial variation in channel adjustments using field indicators was shown to be viable by comparing the results obtained by two independent operators surveying the same reach. Channel change due to the influence of urbanization on the Monks Brook involves capacity increases of up to 2–2.5 times, width increases of up to 2.2 times and bed lowering of up to 0.4 m. The three groups of techniques are capable of being applied to other channels. Channel capacity enlargements are demonstrated to be spatially discontinuous and may involve widening, deepening, or a combination of the two. The character and location of such changes can be an important consideration for channel management.