Submitted to: Management of Landscapes Disturbed by Channel Incision Stabilization Rehabi
Publication Type: Proceedings
Publication Acceptance Date: April 15, 1997
Publication Date: N/A
Interpretive Summary: Drop pipe inlets, sometimes called riser pipes, are field drains formed by small dams with "L" shaped pipes. These structures are frequently used to drain water from fields into creeks that have very steep banks. Drop pipe inlets prevent soil erosion that would occur if water was allowed to run freely over the stream bank. Many of these drop pipes have permanent or semi-permanent pools of water behind their dams. This study showed that pools formed by drop pipe inlets are good for water quality. Sediments and nutrients that would be bad for stream water quality are trapped in the small pools. This study also showed that the deeper the pools the more they helped improve water quality.
Technical Abstract: Drop pipe inlets or field level grade control structures are erosion control measures used extensively in the Demonstration Erosion Control Project in the Yazoo Basin. Typically these structures are constructed with shallow basins that are permanently or seasonally inundated. Pools that provide in-flowing water relatively long residence time play an important role in stream water quality by processing nutrients from storm runoff and trapping suspended sediments. Sixteen drop pipe inlets were divided into four categories based on water depth and surrounding vegetation. Mean depth for categories 1 through 4 were 11.2, 22.7, 42.0, and 173.5 cm respectively. Water quality parameters were monitored to determine significant differences between the categories. Filterable ortho-phosphate was significantly higher in category 1 and 2 pools than the deeper pools, and category 4 pools had the lowest mean total phosphorus concentrations. Category 1 and 2 pools were significantly higher in nitrate than either category 3 or 4; however, category 3 pools had significantly higher ammonium concentrations. The deeper category 4 pools had significantly lower coliform bacteria counts, and suspended and total solids concentrations. Based on these data drop, pipe inlets designed with deeper basins trap coliforms and suspended sediments and process nutrients more efficiently than shallow basin designs.