The SAFL Baffle is a stormwater treatment device created at the University of Minnesota's St. Anthony Falls Laboratory. Previous research by Howard et al. 2011 showed that when the SAFL Baffle is retrofitted into a sump manhole, it improves the ability of the sump to collect sediment at low flow rates and retain captured sediment at high flow rates. The purpose of this research was to know how a SAFL Baffle performs when:
1. Clogged with debris like trash and vegetation
2. Installed in a sump manhole with an outlet pipe 90 degrees to the inlet pipe
3. Installed in a sump manhole with water entering through an inlet grate and inlet pipe Tests were performed at the St. Anthony Falls Laboratory on a 6-ft (1.8 m) diameter by 6-ft (1.8 m) deep sump, a 6-ft (1.8 m) diameter by 3-ft (0.9 m) deep sump, a 1-ft (0.3 m) diameter by 1-ft (0.3 m) deep scale model sump, and a 1-ft (0.3 m) diameter by 0.5-ft (0.15 m) deep scale model sump. All of the sumps were equipped with the SAFL Baffle, and were evaluated using two metrics: 1. How well the system captures sediment at low flow rates (Removal Efficiency Testing) 2. How well the system retains the previously captured sediment at high flow rates (Washout Testing)
When a SAFL Baffle was clogged with stormwater debris, water traveled underneath of the SAFL Baffle. If the sump was deep, performance of the sump equipped with a SAFL Baffle did not change significantly. However, if the sump was shallow, significant washout was exhibited in the sump. This washout problem in shallow sumps was mitigated when a SAFL Baffle with hole diameters equal to 5-in (12.7 cm) was installed in the sump.
Sumps with outlet pipes located 90 degrees to the inlet pipe exhibited significant washout of previously captured sediment during high flow rates. With a SAFL Baffle installed at an angle between 90-120 degrees of the inlet pipe, washout sharply decreased. At low flow rates, a SAFL Baffle installed at a 113 degree angle with respect to the inlet pipe captured more sediment than a SAFL Baffle installed in a standard, straight flow-through sump.
In the sump equipped with a SAFL Baffle that received water from an inlet pipe and an inlet grate from above, washout rates were highest when the flow rate from the inlet pipe was less than the flow rate from the inlet grate. Similarly, the ability of the device to capture sediment decreased when the flow rate from the inlet pipe was less than three times greater than the flow rate from the inlet grate. Through extensive testing, it was determined that the standard sumps equipped with the SAFL Baffle should be used downstream of stormwater sewers such that the drainage basin of the inlet pipe is at least three times the drainage basin of the inlet grate. Under this condition, the flow from an inlet grate from above does not impact the performance of the sump equipped with a SAFL Baffle.
University of Minnesota M.S. thesis. November 2012. Major: Civil Engineering. Advisors: Omid Mohseni, John Gulliver. 1 computer file (PDF); vi, 51 pages.
McIntire, Kurtis D..
Stormwater treatment with the SAFL Baffle: debris and non-standard sump testing.
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