Quantifying the Extent of Aquifer Reduction Due to Floodplain Sand and Gravel Mining

Sand and gravel mining has the potential to adversely affect the hydrogeological properties of alluvial aquifers through direct removal of aquifer material and exposure to surface activities. The coarse-grained portions of a fining-upwards alluvial sequence often comprises the most hydraulically conductive material in these shallow unconfined aquifers. However, gravels and sands are also desirable for construction purposes, and are often dredged from channel bottoms or mined from the adjacent floodplain. A significant amount of sand and gravel mining has occurred within the Brazos River alluvial aquifer, a minor aquifer in Central Texas. Since sand and gravel mining continues to be an important activity in the Brazos River alluvium, identifying and quantifying the extent and impacts of the mining are important for efficient groundwater management. While the various ramifications of instream gravel mining have been studied by many researchers, floodplain sediment mining has not received the same attention. Characterizing the amount of aquifer material removed due to floodplain sand and gravel mining may play an important role in managing the Brazos alluvial aquifer. In this study, historical, spatial, and geological data were integrated in a geographical information system. These data were analyzed using spatial tools in ArcMap to get at an areal estimation of how much material has been removed due to floodplain gravel mining in comparison to total aquifer volume. The total aquifer quantity was estimated using fluvial deposition models for meandering channels and coupled with field observations, core descriptions, and water levels to approximate sediment distribution in the floodplain. Through this analysis, the extent of modification to the Brazos alluvial aquifer through time may be better understood, forming the basis for improving groundwater management in this aquifer.