GROUNDWATER/ SURFACE WATER INTERACTIONS: 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 the surface. Not much is known about the dynamics of these human-constructed lakes which may affect groundwater quantity and quality in the aquifer.

This study examines two gravel-pit lakes in the Brazos River Alluvium Aquifer using mini-piezometers near the lake shore to establish groundwater flow directions and piezometers upgradient and downgradient of each lake to determine if the lakes act as sinks, recharge sites, or flow-through groundwater-fed lakes. A rain gauge was installed at each site and data loggers were installed in selected piezometers nearest to the lake shore. Radon 222 and 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. Preliminary data suggest that the lakes are flow through systems, however during drought periods the lakes may act as sinks. Data will be collected over a calendar year to observe how seasonal changes affect the movement of groundwater through the lakes. Comparing how each gravel-pit lake reacts to the seasonal changes and rain events will provide insight on the variability of groundwater movement through gravel-pit lakes. Even though both gravel-pit lakes are in the Brazos River Alluvium Aquifer, geological differences in the surrounding area can affect groundwater/ lake interactions.