04-13-1998 Council Packet - Laserfiche WebLink

Home Browse Search

r Memo l/]l Boncstfoo Rosene vS Andeiiik & |\j| Associates lAgrwrt 4 Ar«fwi #<t i Water Quantity The topography of this site prevents the entire site to drain to a single ponding area. We offer the following recommendations; 1 It is recommended that impervious surfaces, (house, driveway, and yard) and any land d's^rbed during construction be routed to drain into the street and into the proposed ponding area. This will reduce the amount of untreated runoff draining directly to the lake. 2 The installation of an Emergency Over Flow (E.O.F.) is recommended at the intersection of Outlot A and Old Crystal Bay Road. The E.O.F shall direct the runoff not captured during large storm events to flow overland to the pond instead of out onto Old Crystal Bay Road South. A swale should be graded along the proposed 15-inch RCP pipe system into the proposed pond. 3 A stilling basin lined with rip-rap should be installed between the outlet and the pond to prevent erosion from the high velocities discharging from the 15-inch pipe. A 1-2 ft berm should separate the stilling basin from the pond. The stilling basin should be 15 feet in length with 4:1 side slopes. The stilling basin may not be required if outlet velocities are reduced to 5 fps using some other method. A design in detail should be submitted. 4. Our calculations show a 100-yr HWL of 942.0’, which includes the overland drainage litm V and VI. This HWL seems to provide sufficient freeboard even though the buiiding elevation on Lot 7 is not shown on the plan. 5. The ponding calculations for pre- and post-development for the 5.10. and 100-year storm events should be submitted. 6. The outlet from the pond should be directed easterly under Old Crystal Bay Road to the existing ponding area. A design detail should be submitted. 7 A berm at an elevation of 943.5’ should be installed around the pond. An E.O.F. set at 942.5 ’ ■ should be located on the south east corner of the pond, to allow outflow during storm events larger than the 100-year storm event. The pond E.O.F. should direct the *f>>e;gejhto the west ditch^^^^^ along Old Crystal Bay Road South. The 15-ft. wide E.O.F should be lined either with np-rap or well established vegetation. 8. It is difficult to determine from the grading plan whether a maintenance hen^=hjs being provided above the pond NWL. At a minimum, there should be one provided around the inlet and outlet well as any point where dredging operations might occur. 9 The ponding area should have a 10:1 aquatic bench at the ponds NWL. The ponding area illustrated on the plans submitted on March 15“’ does not appear to have this bench. Bonestroo, Rosene, Anderlik and Associates------------------------------------------- 2335 West Highway 36 ■ SI Paul. MN 55113 ■ Phone. 612-636-4600 ■ Fax:612-636-1311