Investigation of hydrologic and sediment transport processes on riparian hillslopes
Inamdar, Shreeram P.
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Riparian zones are increasingly being adopted as best management practices (BMPs) to control nonpoint source pollution. The effectiveness of these zones in mitigating pollution is a function of the distribution, nature, and rate of water and sediment movement through these zones. The intent of this research was to investigate the influence of site conditions on the hydrologic and sediment transport response of riparian zones/hillslopes. Research investigations were focused in two major areas: field investigations of riparian hillslopes and development of a riparian hillslope model. The objective of the field investigations was to characterize and quantify geomorphic features of riparian slopes that can be used to quantify flow concentration on hillslopes. The riparian hillslope model was used to investigate the dynamics of hydrologic and sediment transport processes. Field investigations revealed that riparian hillslopes were dissected into distinct convergent, divergent, or straight slope segments. In profile, these segments were either concave, straight, or convex. It was hypothesized that the size of such segments reflects the "representative hillslope scale". Probability distributions of catchment area showed that catchment area decreases with slope gradient. Distributions of catchment shape revealed that catchment shape elongates with increasing gradient. Distributions of drainage channel cross-sectional shape data showed a decreasing trend in width to depth ratio with increasing slope gradient. These results indicate that geomorphic features characterizing flow concentration vary with slope gradient and should not be neglected when simulating riparian hillslopes. Model simulations revealed that site conditions such as slope gradient, slope shape, flow concentration, and soil horizon thickness and characteristics play a significant role in shaping the hydrologic and sediment phenomena on these hillslopes. These results underscore the need for evaluation of riparian zones considering specific site conditions. Interflow was the dominant hillslope runoff mechanism. A large fraction of the interflow occurred via macropores. Macropore flow was orders of magnitude quicker than soil matrix flow. Overland flow was found to occur primarily due to saturation excess or return flow. Simulations showed that thinning of soil layers and/or concave-convergent slope shapes provide favorable conditions for generation of saturation excess or return flow. Sediment delivery down the slope increased with increasing flow concentration.
- Doctoral Dissertations