Abstract
Abstract A small-scale water harvesting structure known as a sand dam has gained popularity across East Africa due to the efforts of non-governmental organizations. A sand dam is a subsurface water reservoir that stores water between sand grains. Stored thus, the water is filtered and protected from evaporation. This study uses remotely sensed data to investigate the impact of these structures on water storage and vegetative growth. The relationship between sand dams and water storage was modeled using a binary sand dam factor, climate data from the Famine Early Warning Systems Network Land Data Assimilation System (FLDAS), and water storage data measured by the Gravity Recovery and Climate Experiment (GRACE) twin satellites. The analysis revealed that GRACE largely fails to detect a statistically significant impact of sand dams on regional water storage. However, analysis of the Normalized Difference Vegetation Index (NDVI) indicated that sand dams have a significant impact on regional vegetation. Vegetative growth is correlated with groundwater levels, indicating that sand dams have a positive impact on water storage albeit on a smaller scale than GRACE can regularly detect. Significantly, this study shows that NDVI data can be used effectively to study small-scale, regional changes in vegetation and water storage.
Highlights
The methodology included here outlines two techniques for quantifying the impact of sand dams: one using Gravity Recovery and Climate Experiment (GRACE) total water storage and one using Normalized Difference Vegetation Index (NDVI). Both techniques are based on developing a generalized linear model that seeks to define the relationship between the presence of sand dams and a magnitude of change in GRACE data or NDVI data
The study revealed that sand dams likely do not significantly affect regional groundwater levels beyond a few months of the year
The GRACE total water storage data indicates that sand dams capture and store additional water during the rainy season, but that this additional storage is not significantly greater than water storage in an area without sand dams beyond the 2 months of the year with the most rainfall
Summary
One of the world’s grand challenges, addressing the problem of water insecurity, is problematic in developing. This is especially true in poorly connected rural communities, where women and children might spend 3–4 h a day collecting water (Henry et al ). Merwade | A data-driven approach to assessing water harvesting structures in East Africa
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