Modeling Land Use Change and Associate Water Quality Impacts in the Ambos Nogales Watershed, US-Mexico Border

by Norman, Laura Margaret.

The twin city area of Nogales, Arizona and Nogales, Sonora, Mexico, known collectively as Ambos (both) Nogales, has experienced a common borderland history of urban growth presumably based on changes in policy and economic incentives. This research documents changes through time in an attempt to identify colonia (settlement) development and patterns along the U.S.-Mexico Border, combining a community participation approach with remote sensing analyses, to create an online mapping service. This study outlines a planning approach that is meant to promote sustainable development in the future, integrating both sides of the border. Urban area classifications for this watershed were created from images for early summer 1975, 1983, 1996 and 2002 as part of a research project to monitor colonias growth performed under a grant from the U.S. Department of Housing and Urban Development. This dataset was used as input to the Clarke urban growth model, called SLEUTH, to predict land use changes to the year 2030. Erosion-sedimentation models were applied to generate simulations of potential sources and sinks in the watershed. The Universal Soil Loss Equation (USLE), an empirical formula used to predict potential average annual soil loss in tons per acre per year (t/a/y), was applied to the study area. In order to calculate the location specific net sediment delivery in the watershed, the Spatially Explicit Delivery Model (SEDMOD) was employed, to quantify the amount of sediment that is deposited. In an effort to forecast the effects of urban development in 2030 on downstream water quality, changes 15 predicted in urban growth by the SLEUTH model were retrofit to the erosionsedimentation models. Using techniques designed to protect the previously identified erosion ‘hot spots’, alternate scenarios were generated, depicting better water quality possibilities if these guidelines could be adhered to. In this study, I provide (1) a new methodology for assessing future erosion impacts in urbanizing watersheds, (2) a quantification of urban sprawl and its implications for water quality, and (3) the generation of alternative future scenarios for management of downstream sedimentation. 16