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I I I Council Meeting Minutes June 12, 1995 Page 8 Council Business. continued The Ulteig engineer felt that according to the survey, a 9-inch orifice could be used if the grading was done per the final flow rate determined in 1993. If a larger orifice is installed, it will significantly change how that pond reacts. Benke asked if a larger orifice was installed in Pond 3/4 would it affect Pond 5. Melcher said Pond 5 was designed with a lO-inch orifice and two backups. The backups allow the water to rise one foot and travel into a pipe, or a redundancy is built into the pond if a blockage occurs. Melcher said the resident adjacent to the area has not had problems. Williams noted concern that ponding occurred after a 2-inch rainfall. Proper witnessed that not only was water running out of the orifice, but was draining over land. Williams asked if a larger orifice would remedy the problem. Proper feels it may take care of the problem, but noted concern regarding Pond 5. There was a tremendous amount of water in Pond 2 which took 24 hours to pump down to a point for the outlet to be unplugged. Williams asked when the 6-inch orifice could be installed in Pond 2. Proper said the City consultant received some desire on the developer's part to install an apron section and round grate for the inlet from Pond 2. If the developer did this there would be no point in installing the orifice. Williams asked if the stated modifications were made to Swale 2, would the orifice be needed. The Harstad recommendation states the water would go into the pipe and retained in Pond 3/4. Benke asked if Pond 3/4 could hold water if a lO-inch orifice was installed. Proper has reservations of this especially after the weekend rainfall. In addition to water traveling through the orifice, it was also draining around the soccer field and running over the surface. There was a tremendous amount of water, and because Swale 2 was plugged that means none of that water actually got into the system. Proper said that on paper it looks like it should work, but the pond was very high and because there is much hard surface area there could be future problems. Williams asked how much larger would Pond 3/4 be increased. Harstad said that if the orifice was opened, the flow would increase 35 % and regrading should help. Benke asked if the project includes excavation to accommodate the mitigation of the siltation that occurred in Pond 3/4. Harstad said siltation work will be performed and the pond's capacity will increase because of a high absorption rate of the sandy soil. He ensures the net result will improve the area, and opening the Swale 2 pipe would dispense the same amount of water. Williams questioned that if this proposal was approved and Pond 5 did overflow from being unable to accept the additional flow, who will be liable for water damage. Melcher said RCWD approved the plan, and many other parties are associated with the project. Williams asked if Harstad would have liability in this issue. Harstad acknowledged that this is a legal question, however, he suspects they would be some joint responsibility. Williams likes the idea of shared risks. Benke said the slope on the south side of Swale 2 appears to be steep and past discussions noted concern of children falling in and being unable to climb out. Proper said the swale design was stated in the approved plan. Benke said the contours of Swale 2 appear to be steeper than Pond 3/4. Harstad acknowledged that this was an engineering "boo-boo" and it is too steep to maintain. Until this issue is resolved, the steepness will be a continuing problem. Council Business Innsbruck Park Estates Ponding Area Report 95-104