container 10 also has at least one inlet 13 into primary chamber 15 and at least one outlet 14 from outlet chamber 33 the second embodiment also includes a low flow conduit 17 that has an inlet opening 30 in an upper surface at the first end of the conduit 17 situated within chamber 15 for allowing surface water to flow from chamber 15 into the conduit 17 conduit 17 empties into chamber 16 through opening 31 in the interior dividing wall 12 the discharge into chamber 16 is above the surface level of the fluid in chamber 16 during normal flow conditions a subsurface control plate 35 attached to the low flow conduit 17 and extending from the interior wall of container 10 to the dividing wall 12 diverts water under conduit 17 for moderate flow conditions when the level of the water exceeds the lower entry edge of moderate bypass flow opening 38 in dividing wall 12 the surface water on the back side of conduit 17 is isolated from the surface water on the front side because conduit 17 and subsurface control plate 35 extend from the interior wall of the chamber 10 to the dividing wall 12 by isolating the water surface and diverting flow below the subsurface control plate 35 floating debris in chamber 15 will be prevented from reaching the back side of conduit 17 and therefore cannot flow out the lower portion of opening 38 a single opening 38 can function as the moderate and bypass flow opening 38.