Date of Award

Spring 1-1-2017

Document Type

Thesis

Degree Name

Master of Arts (MA)

First Advisor

Holly R. Barnard

Second Advisor

Brian A. Ebel

Third Advisor

John Pitlick

Abstract

Land-use in the tropics has changed dramatically with increased conversion of forests to subsistence farms and cattle pastures. Land-use change alters soil properties that drive the hydrological processes of infiltration and surface runoff generation. We compared surface runoff generation between two steep, humid, tropical lowland catchments in Panama: a mature forest and an actively grazed cattle pasture. Soil hydrologic properties, soil moisture and surface runoff were measured along hillslopes of each land-use type. We parameterized the numerical model HYDRUS-1D with soil characteristics and rain event data to simulate surface runoff, which was then compared to that observed at the forest and pasture. Runoff ratios were generally higher at the pasture site, though we did not observe any overall trends between rainfall characteristics and runoff ratios across different land-uses. We did observe significant differences in saturated hydraulic conductivity (Ks), bulk density and porosity between the forest and pasture (p < 0.05). Surface runoff simulated in HYDRUS-1D produced outputs similar to observed surface runoff at the pasture, but little to no surface runoff was predicted at the forest. Results from our study suggest the combination of a leaf-litter layer and the activation of shallow preferential flow paths are the main drivers for surface-runoff generation at the forest site, while Hortonion overland flow is the main driver for surface runoff at the pasture site. Results from this study contribute to the broader understanding of the delivery of stormwater to streams, both in terms of timing and quantity, which will become increasingly important in the tropics in light of freshwater resource scarcity.

Included in

Hydrology Commons

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