Spatially Identification of Sites to Capture Stormwater Runoff Using Geographic Information Systems in a Small Coastal Basin
Reliable runoff estimation and identification of places to naturally capture stormwater are important for designing water infrastructure in small agricultural catchments. Factors such as basin scale, human activities and natural physiography vary from one place to another. Thus, the key challenge for water managers and decision makers is to select the best strategy of sustainable practices for implementation to achieve the most viable and practical management approach for the location of interest.
In northern Mexico, water resources management has become a challenging task, aggravated by the vulnerability of this region to persistent drought conditions and climate change. Located in northwest Baja California, the Guadalupe River Basin has three main valleys, Ojos Negros, Guadalupe and La Mision. It is situated in a coastal semiarid region with an outlet to the Pacific Ocean. This study was focused in the Guadalupe Valley with a surface area of about 976 Km2 with agriculture, primarily grapes and olives, to be the predominant land use. The region is semiarid facing high interannual rainfall variability, and most of the total annual precipitation is dictated by seasonal autumn-winter rainfall as it is the flow and capacity of streams. In addition, the valley is under additional pressure due to wine production and drinking water supply, thus the sustainable use of water resources becomes a priority.
The present study was focused in identifying the most suitable areas for water capture in an agricultural valley of a coastal watershed. In contrast to urban development, where the conventional drainage solutions could contribute to flooding because of a faster stormwater transfer; in small agricultural communities located in semiarid areas, stormwater transfers occur in a natural hydrological cycle. The main objective was to spatially identify possible runoff capture areas in the Guadalupe Valley to be considered in a sustainable watershed plan. Our analysis framework may provide water managers and decision makers with an approximation of optimal places to store stormwater or promote infiltration that could be serving as an option for further scenarios for mitigating drought impacts.
The methodology consisted in performing an analysis using geographic information systems that explicitly represents the land cover information and surface components of the basin flow routing. The first step was obtaining map data of surface streams, topographical gradients, digital elevation model, geological composition, and land use coverage. Then, using these maps as in input, the best areas for capturing water were identified by performing a spatial analysis using geographic information systems. In addition, historical well depth measurements were explored, and recent water levels were obtained with in-situ measurements. The purpose was to locate those wells that during raining season were recovering water levels. After obtaining the polygons for optimal stormwater capture, green infrastructure was recommended. The hydraulic proposed infrastructure included: check dams to delay runoff and promote infiltration; wetlands to enhance water quality; and small dams to storage water for agricultural irrigation purposes.
Results shown the primary and secondary optimal location of infiltration-based stormwater capture areas. The delineation of these sites depended also on well water depths field measurements. In addition, to provide water storage and/or aquifer recharge infrastructure solutions, the proposed sites were traced near local material banks so it could contribute to a low cost infrastructure. The outcome of this study may be used by decision makers to develop a sustainable local-valley scale water resources management plan that includes water capturing while providing protection to groundwater using an optimal combination of strategies.