An Automated Seepage Meter for Streams and Lakes

We describe a new automatic seepage meter for use in soft bottom streams and lakes. The meter utilizes a thin-walled tube that is inserted into the streambed or lakebed. A hole in the side of the tube is fitted with an electric valve. Prior to the test, the valve is open and the water level inside the tube is the same as the water level outside the tube. The test starts with closure of the valve, and the water level inside the tube changes as it moves toward the equilibrium hydraulic head that exists at the bottom of the tube. The time rate of change of the water level immediately after the valve closes is a direct measure of the seepage rate (q). The meter utilizes a precision linear actuator and a conductance circuit to sense the water level to a precision of about 0.1 mm. The meter can also provide an estimate of vertical hydraulic conductivity (K-v) if data are collected for a characteristic time. The detection limit for q depends on the vertical hydraulic head gradient. For K-v = 1 m/day, q of about 2 mm/day can be measured. Results from a laboratory sand tank show excellent agreement between measured and true q, and results from a field site are similar to values from calculations based on independent measurements of K-v and vertical head gradients. The meter can provide rapid (30 min) q measurements for both gaining and losing systems and complements other methods for quantifying surface water groundwater interactions. Key Points New seepage meter for streams and lakes has been developed Rapid seepage rate measurements can be made for several days The device can measure water levels to +/- 0.1 mm