I am trying to determine the entrance loss benefits of changing the entrance conditions from water run-off (gravity flow) from a smooth (steel plate) surface into a rectangular channel box that is under induced suction. Currently, I believe that I am restricting water removal-flow through a rectangular, slotted entrance but am not sure how to calculate the potential benefits of increasing slot size, changing shape, etc. Attempting to remove approximately 3,000 US gallons per minute through a slot of 2.75-inches x 48-inches. I need to improve loss conditions by minimum of 12-inches of head in order to gain an appreciable benefit. HELP PLEASE!