Pollution in stormwater runoff collects in retention basins. Sewage may include stormwater runoff or urban runoff. The dam worked by retaining stormwater runoff in a reservoir. For the river passes through a basin fed primarily by springs and stormwater runoff. It can prevent erosion caused by excessive rain that might result from surface runoff. Plans will include methods for damming gullies and reducing rainwater runoff. Water flows out of wetlands by evapotranspiration, surface runoff, and subsurface water outflow. Nutrient losses in runoff and leachate are often associated with agriculture. If rainfall occurs at a rate faster than the infiltration capacity runoff will occur. The roots then improve water quality by consuming nutrient pollutants, such as from agricultural runoff. It was also built without adequate planning for storm water runoff. Agricultural runoff and wind blown debris are prime examples. In 2001, scientists estimated that farming contributed 38% of the phosphorus runoff. Shafik collected 48.3 percent of the vote in the presidential runoff. The lead-up to the runoff election was contentious.