Quantification and Scaling of Infiltration and Percolation from a Constructed Wetland: Fid-Bau Portal

Quantification and Scaling of Infiltration and Percolation from a Constructed Wetland

Stewart, Ryan D

AbstractEfforts to prevent temperature increases in streams and rivers have led to regulation of the maximum permissible temperature for wastewater discharges. Hyporheic discharge treatment, where warm wastewater is allowed to infiltrate into the soil and percolate toward the stream, has been proposed as an alternative management practice, potentially providing increased streamflow at decreased temperature. To assess the feasibility of such a system, a pilot study was performed in which groundwater level, temperature, and chemistry were monitored to characterize percolation from a 0.15-ha infiltration wetland. The temperature patterns suggested that water seepage rates exceeded 1.6 md−1 near the wetland, while the chemistry data indicated that infiltrated water had laterally percolated more than 100 m during the study period. The water level and temperature measurements were also used to calibrate a software model. Observations and simulations showed that the local water table became directly connected to the wetland. As a result, much of the water infiltrated through the wetland perimeter rather than through the wetland center, which implies that specific infiltration rates will decrease with increasing wetland size. This theory was tested using two approaches: (1) numerical simulation of a large-scale (5.5 ha) infiltration wetland; and (2) a water budget performed on an adjacent low-lying, inundated section of the floodplain, which due to its topography was considered to be an accurate approximation of the performance of a large-scale system. The water budget approach indicated a mean seepage velocity of 0.08 md−1, which was essentially equal to the predicted seepage velocity for a large-scale infiltration wetland of 0.077 md−1.