Conceptual, algorithmic, and statistical exploration of relations between runoff generation, stream geomorphology, and watershed topography in West Texas



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This Dissertation contains four separate, free-standing, but related documents. The common theme is the relation between geomorphology and hydrologic response.

  1. Moving Substrate in an Ephemeral Stream: A Case Study in Bridge Survival

(Republished with permission of the Transportation Research Board.)

A case study concerns a small bridge site in an arid area where ongoing inhibition of the transport of bed load sediment has caused chronic problems and maintenance issues for many years. The crossing of Guadalupe Arroyo by coaligned US1 Highways 62 and 180 exhibits many unusual and important characteristics that are seldom seen in one place. Evidence exists of large magnitude transport of very large particles on a regular basis, to the extent of requiring protection of the piles from boulder impacts. A large lens of bed material has accumulated upstream and extends approximately 1,000 ft (305 m) from the bridge. This site presents a rare opportunity to study an extreme case of the inadvertent inhibition of the transport of bed material in an ephemeral desert stream by the construction of an otherwise ordinary and innocuous highway bridge.

  1. A Generalized Additive Model (GAM) for Stream Discharge and Velocity Estimation from Stream Geomorphology

A discussion of work that was inspired by and resulted from discussions between the author and colleagues from various universities and from the U.S. Geological Survey (USGS) during and after the study of Guadalupe Arroyo documented in the previous chapter of this dissertation. The focus is on the validation of hydrologic techniques, hydraulic modeling, and bridge scour analyses.

  1. The Effect of Terrain Ruggedness on Runoff Generation and Flood Magnitude This chapter constitutes a study of the influence of both terrain ruggedness and areal proximity on flood magnitude. Discussion and conceptualization of the influence on the runoff process of parts of a watershed far distant, versus those more proximate, to a point of interest. Case studies illustrating the point are observed by the fact that distinct differences in proximal influence are magnified by the ruggedness the terrain of proximate areas. The case examined involves increase in the ruggedness of the proximal terrain through which the main stem of the lower Pecos River flows.

  2. A Probabilistically Based Alternative to Unit Hydrograph Watershed Modeling This chapter discusses conventional Unit Hydrograph modeling, then presents an alternative method of watershed modeling. The alternative method is based on the concept that the survival of a raindrop to traverse the watershed and exit is a random variable. The proposed model replaces the unit hydrograph and loss model with a time-area relationship, randomly generated variates from the either the exponential or the Weibull distribution, and a comparison between variate magnitude and the time needed to exit the watershed. A conceptual study and case studies demonstrate that the model can reasonably represent real rainfall-runoff data.



Hydrology, Runoff, Hydraulics, Sediment transport