GRAVEL PIT LAKES IN THE BRAZOS RIVER ALLUVIUM AQUIFER

Urban expansion and the subsequent need for construction materials are increasing aggregate mining activities in many areas around the world. In central Texas much of the aggregate has come from alluvial sediments in the Brazos River valley which also comprise the Brazos River Alluvium Aquifer. Aggregate mining is exempt from many reclamation requirements and the result is a series of post mining gravel-pit lakes in the Brazos River Alluvium Aquifer exposing the aquifer to surface conditions. Not much is known about the dynamics of these human-constructed lakes which may affect the groundwater quantity and quality in the aquifer.

This study examines two gravel-pit lakes in the Brazos River Alluvium Aquifer using piezometers upgradient and downgradient of each lake to determine if the lakes act as sinks, recharge sites, or flow-through groundwater-fed lakes. Piezometers were installed upgradient and downgradient of these gravel pit lakes to measure changing groundwater elevations and a lake gauge was installed at each lake to measure changing surface water elevations. Isotopes of deuterium and oxygen eighteen were used to assess the longer-term impacts of the lakes and to support the direction of groundwater flow. A 2D finite element model will be used to help further understand the groundwater flow dynamics through the system. Data have been collected over a calendar year to observe how seasonal changes affect the groundwater elevations and groundwater movement through the gravel-pit lakes. Preliminary data based on water elevation and isotopic values suggests that both lakes are flow-through systems throughout the year.