GEOMORPHIC AND HYDROCLIMATIC INFLUENCES ON THE SPATIAL SCALING OF FLOODS AND CHANNEL CHARACTERISTICS, ATLANTIC SLOPE WATERSHEDS

The frequency and magnitude of flooding in a river network is determined by both hydro-climatological and geomorphological characteristics of the watershed. Understanding how these characteristics influence flood magnitude and channel response can provide insight into the evolution of the river networks under different climatic and geological conditions. The relationship, Q=αA^θ, of stream discharge (Q) to drainage basin area (A) is used in both flood prediction and landscape evolution models. In the first part of this study, scaling parameters (α, θ) were compared across major Atlantic Slope river basins in order to examine variations in the scaling parameters with the hydro-climatic and geomorphic setting of the basins. Atlantic Slope basins were selected due to the North-South variations in hydro-climatology (relative frequency of tropical storms) and geomorphology (glaciated versus non-glaciated) within this region. Results indicate that scaling exponents (θ) are lower in southern basins, indicating more effective dissipation of flood peaks compared to northern rivers. Additionally, the 50-year and larger recurrence interval floods have higher relative magnitudes in southern watersheds, reflecting the higher proportion of tropical storms and hurricanes in the flood record of southern rivers. The Potomac River basin is transitional, with flood magnitudes similar to the southern watersheds, but scaling exponents similar to northern watersheds indicating little downstream dissipation of flood peaks. To quantify the geomorphologic characteristics that influence flood peak dissipation, we investigated the at-a-station and downstream hydraulic geometry of the study river systems and used hydraulic geometry and flow duration analyses to develop velocity probability distributions that are compared among the basins.