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HomeMy WebLinkAboutPrelim Taylor Loop Drainage Analysis - 15% SubmittalWhite-Daters & Associates Consulting Engineers Taylor Loop Road Drainage Analysis -15% Submittal 12/4/2013 Chenal Valley Improvement District 14 Regional Storm Water Detention Facility Developed Drainage Basin 376 Acres 25 Year Developed Conditions Release 549.1 CFS 100 Year Developed Conditions Release 796.1 CFS Basin Area below District 14 Detention Facility and Taylor Loop Road Basin Area 77.05 Acres Additional Stream Length 2510 Linear Feet Assume average channel flow velocity of6 6 Feet per second Travel time 418 Seconds 7 Minutes Time of concentration for lower basin is 42 Minutes Based on 35 minute time of concentration for detention area 25 year event I (intensity for 42 minute storm) =3.9 in/hr c (runoff coefficient)0.6 Area of 77.05 Acres Additional Flow 180 CFS Total Flow to Taylor Loop based on CV District 14 Detention Detention Area 549.1 CFS Downstream Area 180 CFS Total 729.1 CFS Quick Check Comparison Total Drainage Area 453 Acres 25 year event I (intensity for 30 minute storm) =5 in/hr c (runoff coefficient)0.65 Rate 1472.4 CFS Use 1,472 cfs to be conservative. Much of the upper basin is still undeveloped and it is probable that small localized detention facilities will be of minimal benefit Analysis of Double 48" RCP under Taylor Loop at Gooch Combined area is 25 Square Feet Probable Velocity 8 Feet per second Max Flow Rate 201 CFS Flow through new box culvert under Taylor Loop, East of Gooch Road Total flow 1472 CFS Flow through Dbl 48"201 CFS Net flow at new Box Culvert 1271 CFS Preliminary Design for Taylor Loop Box Culvert Sufficient headroom for a 5' tall box culvert Maximum span of 12' Dbl Culvert provides 5 x 12 x 2 = 120 square feet of waterway opening Full flow velocity of 1171 cfs/120 sf =10.6 feet per second Comment: The velocities in the 48" culverts and 5' x 12' Box Culverts are reasonable For preliminary design proceed with these structures Note: Detailed analysis shows overtopping of Taylor Loop with this configuration consider 6' tall dbl box to increase capacity. Further investigation of potential utility conflicts and downstream impacts.Follow up Req'd Preliminary Design for Gooch Drive South Box Culvert Sufficient headroom for a 5' tall box culvert Maximum span of 12' Use single box section with overflow over Gooch Road North Capacity of box culvert at 8 feet per second 480 CFS Balance of flow over Gooch Road South Total Flow 1472 CFS Dbl 48"201 CFS Single Box Culvert 480 CFS Overflow 791 CFS Conservative overflow velocity is 3 feet per second Therefore: 263 square feet of flow area for overflow Sufficient overflow area in all likelihood exists South of Taylor Loop Road, but need to confirm with overland flow analysis Follow up Req'd Summary of Preliminary Design - South of Taylor Loop Road Drainage Area 453 Acres 25 year flow 1472 CFS Flow through Dbl 48" Culverts 201 CFS Flow through Box Culvert on Gooch South 480 CFS Flow over Gooch South 791 CFS Flow under Taylor Loop in Dbl Box Culvert 1271 CFS Open Channel Flow Analysis South of Taylor Loop Road 20 foot flat bottom channel 4 foot depth 1.5% Long Slope 3;1 side slopes Roughness, n=0.045 Capacity 1035 CFS Velocity 8 feet per second As an alternative 24 foot flat bottom channel 3.7 foot depth 1.5% Long Slope 3;1 side slopes Roughness, n=0.045 Capacity 1028 CFS Velocity 8 feet per second With lower n values 20 foot flat bottom channel 3.3 foot depth 1.5% Long Slope 3;1 side slopes Roughness, n=0.030 Capacity 1077 CFS Velocity 10.9 feet per second As an alternative 24 foot flat bottom channel 3 foot depth 1.5% Long Slope 3;1 side slopes Roughness, n=0.03 Capacity 1048 CFS Velocity 10.6 feet per second Conclusion for preliminary design: The new ditch section, down stream from the double box culvert installation on Taylor Loop Road will require a 20 foot to 24 foot wide flat bottom ditch section with 3:1 side slopes and flow depths of 3 feet to 4 feet. Total easement width required will be approximately 45 feet.Follow up Req'd Downstream Considerations Glen Valley Drive Approximately 1.050 feet downstream of the Taylor Loop culvert crossing is the double culvert crossing under Glen Valley Drive. The double corrugated metal arch pipe culvert crossing at this street has approximately 18" of available head on the upstream head wall. The culverts slope approximately 3" across a distance of 40 feet. Prior to overtopping Glen Valley Drive the culverts can be expected to achieve a velocity of approximately 8 feet per second for a flow rate of 30 sf x 8 = 240 CFS. This rudimentary analysis of the street crossing indicates that the existing culvert crossing under Glen Valley Drive is not adequate to pass the 25 year event under the roadway. Once overtopped water flow to the west and north along Highlander Drive and to the east and north to the low area on Clancy Court. Form anecdotal information the existing underground storm drainage piping will not accommodate the 25 year event Consideration of additional downstream improvements is warranted.. Improvements to the drainage structures under Taylor Loop upstream form this location will marginally increase flow rates. Follow up Recommended