The use of remote sensing and modelling to detect small-dam influences on land-use changes along downstream riparian zones

A land-use change detection analysis was performed on a headwater basin to assess the influence of floodwater control structures on riparian zone development over a ∼30 year period (1973–2001). Multitemporal satellite datasets were used to compare vegetation and leaf area index (LAI) changes in the riparian zones of 33 impounded reaches to 33 non-impounded reaches within this basin. Results showed a significant increase in woody vegetation for both groups, but a compositional shift toward more riparian species along the reaches downstream of dams (6% in 1973 and 39% by 2001). LAI over the ∼30 yr period increased significantly along impounded streams, and indicates potentially wetter soils along bank environments for these reaches. Stream water discharges for a typical 2 yr flood event were analyzed using the Soil Water Assessment Tool (SWAT) software, simulating with and without-dams scenarios to compare total recession-flow differences. Flow-recession discharge from dam totals were generally greater than non-dammed stream scenarios because of increased water residence time from prolonged outflow. The average annual basinwide water budget showed the dams increase groundwater recharge, deep aquifer recharge, and revaporation to the soil layers.