Electronic Theses and Dissertations

Date

2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Civil Engineering

Committee Chair

Claudio Meier

Committee Member

Dorian J Burnette

Committee Member

Robert L Hunt

Committee Member

Farhad Jazaei

Abstract

Runoff generation in a watershed is a highly complex process whose estimation is vital in performing engineering tasks such as flooding risk assessments and design of hydraulic structures. Because natural rainfall-runoff processes are complex and inherently nonlinear, they are difficult to quantify or parametrize. In engineering hydrology, this issue has been mostly circumvented by using highly simplified, lumped approaches. Typically, losses are abstracted from a total precipitation hyetograph (representing either an actual or a design storm, depending on the application) to obtain the effective rainfall component, that is understood to result in the corresponding flood event. Then, this effective precipitation is converted into direct runoff, assuming that the basin’s effective rainfall - direct runoff transfer function, i.e., its unit hydrograph (UH), is unique and that the basin response is linear. Recent studies on watershed rainfall-runoff response have mostly focused on adding more complexity to spatially distributed, dynamic models, which are purported to be physically based, attempting to incorporate some of the processes behind the simpler runoff-generation mechanisms, such as that of Horton. However, such models necessarily require data-intensive descriptions of the spatial variability in rainfall input and basin’s characteristics. In this study, we analyze rainfall-runoff responses with simplified lumped approaches like the UH method. These are still extensively applied as they underlie most hydrological methods sanctioned by US Federal agencies. After deriving UHs for a large number of selected events in five rivers of West Tennessee, we observe that these vary widely for each watershed, contradicting the prevalent notion of linearity in response, as represented by a single, average UH. However, for all studied basins, the variability in the resultant UHs can be well explained by two variables related to the watershed’s antecedent conditions: the base flow at the beginning of each event and the average antecedent soil moisture condition. Based on this, we propose a variable-UH methodology, that is satisfactorily applied to rainfall-runoff modeling at the event scale as well as flood forecasting. Our results could be used to generate simple, deterministic rainfall-runoff methods that are able to independently account for the effect of a basin’s antecedent conditions.

Comments

Data is provided by the student.”

Library Comment

Dissertation or thesis originally submitted to ProQuest.

Notes

Open Access

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