UC Berkeley

Land and water degradation endangers the livelihood of millions of people who are dependent on natural resources. The negative impacts of land and water degradation include loss of topsoil, water scarcity and reduced productivity of agricultural or natural ecosystems, as well as costs associated with mitigation measures like water treatment. Addressing land and water degradation is therefore central to ameliorating poverty and food insecurity, particularly in rural areas and developing nations. Soil and Water Conservation (SWC) practices are a wide range of land management and agricultural interventions designed to address land and water degradation. However, there are several challenges that impair the successful design, implementation, and adoption of SWC practices. These challenges include the limited success of top-down, non-participatory planning approaches, and disincentives to adopt SWC practices including insecure land tenure, financial constraints, and maintenance requirements. My dissertation focuses on two more technical challenges: (i) lack of simple and low-cost measurements to assess SWC impact which undermines the financing entity's confidence in supporting implementation of new SWC practices; (ii) lack of information about the performance of SWC practices under different climate, landform and soil types which may lead to inappropriate implementation of SWC practices that exacerbate land degradation. To address these challenges, I take advantage of several relatively well-monitored project sites in the Ethiopian Highlands - a region that experiences some of the most dramatic rates of soil erosion in the world.

In Chapter 2 I address the need for low-cost SWC evaluation methods, using existing but incomplete datasets to evaluate SWC performance in five micro watersheds. I develop a method to assess change in runoff ratio and sediment loss in the absence of a flow rating curve to relate stream flow to stream depth, by using stage (flow depth) measurements only. I use the results to compare runoff production and soil erosion to areal coverage of SWC. In Chapter 3 I tackle the difficulty of predicting SWC practice performance in new sites by exploring soil controls on runoff generation in the Ethiopian Highlands.I present observations of soil hydraulic properties across profiles and along hillslope transects and test the runoff generation to the vertical structure of soil textures. The work highlights the risk of current soil evaluation practices which consider only soil surface textures. I generate the first soil water retention curves for soils in the Ethiopian Highlands and evaluate the performance of tropical pedotransfer functions to predict these soil hydraulic properties. This reveals the importance of clay composition as a primary regulator of soil behavior in the Ethiopian Highlands. In Chapter 4, I synthesize my field investigations in a two dimensional synthetic modeling exercise, which investigates the potential of using existing tree crops such as Eucalyptus for biodrainages, as an alternative to physical SWC practices and identify plant hydraulic traits that influence the efficacy of biodrainages.

My dissertation is focused in the Ethiopian Highlands, but the methods developed, key findings, and knowledge gaps identified in my work are relevant to resource-constrained and soil erosion-prone regions globally.