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In order to improve the performance of standard sumps as a best management practice (BMP) in treating stormwater runoff, a baffle was designed to be installed as a retrofit in standard sumps. The retrofit is a porous baffle called "SAFL Baffle." The effect of the SAFL Baffle on the performance of standard sumps was assessed by conducting laboratory tests on small scale as well as full scale straight flow-through standard sumps equipped with the baffle. In addition, a number of tests were conducted to determine the performance of standard sumps with the SAFL Baffle when the baffle is clogged with debris like trash and vegetation. Furthermore, the performance of two other configurations of the baffle was studied: (1) the SAFL Baffle in a sump with an outlet pipe 90 degrees to the inlet pipe, and (2) the SAFL Baffle in a sump with some water entering the sump through an overhead inlet grate. Standard sumps equipped with the SAFL Baffle were evaluated using two metrics: (1) How well the system captures sediment during low flow conditions (Removal Efficiency Testing), and (2) how well the system retains the previously captured sediment during high flow conditions (Washout Testing). The results of the tests showed that the SAFL Baffle dissipates the energy of water entering the sump and as a result, at low flow rates, it captures sediment better than a standard sump with no baffle. More importantly, at high flow rates, the washout of the previously captured sediment reduces to near zero. Vol 1 is 2011-08.

Hydrodynamic separators are widely used in urban areas for removal of suspended sediments and floatables from stormwater due to limited land availability for the installation of above ground stormwater best management practices (BMPs). Hydrodynamic separators are often sized based on 2-yr stormwater runoff from the drainage basins that they serve. However, during less frequent storm events, e.g. 10-yr storm events, device design treatment rates are exceeded and previously captured sediments can be scoured and washed out. At the St. Anthony Falls Laboratory, three devices have been studied and tested and, subsequently, a testing method has been developed to assess sediment retention in hydrodynamic separators under flow rates exceeding their maximum design treatment rates (MDTR). This new testing protocol has been used in controlled field and laboratory tests on full-scale commercial devices under high water flow conditions to determine sediment retention performance of hydrodynamic separators. In addition, velocity profiles have been taken to observe the complex flow patterns in these devices. Application of this work is primarily to establish the frequency of required cleaning for installed devices.