Dynamic Routing Applied to an Urban Subsurface Drainage System

Transcription

1 Dynamic Routing Applied to an Urban Subsurface Drainage System Michelle Iblings, PE, CFM (Freese and Nichols, Inc.) Jim Dulac,, PE (City of Richardson) TFMA Spring Conference May 1, 2008

2 Project Overview Routing Methodologies Comparison of Results System outfall Downstream of outfall Practical modeling considerations

3 Project Location Floyd Branch Beltline Large diameter Box Culvert system Watershed is highly urbanized I-75 Kaufman Outfall Existing site includes retail, 10-story bank building, industrial facilities, and Spring Creek BBQ Open channel crosses several major roads and DART downstream

4 Project Overview Study Phase Hydrologic model in HEC-HMS 8 total basins contribute 500 ac to Kaufman LAG ROUTINGS for large pipes Hydraulic model in HEC-RAS Upstream study limit = Kaufman outfall (3-9 x7 ) Kaufman Outfall

5 Existing Infrastructure JB in NB 75 Frontage Road

6 Existing Infrastructure JB in NB 75 Frontage Road Standing in 9 x6 ; looking at 2-7 x4 outfall to the south and 5 x4 inlet from the west

7 Project Overview Concept Phase Preliminary improvements to upstream pipe system Hydraulic analysis in StormCAD User input peak flows from HMS Manual flow splitting for existing and proposed conditions Proposed alternatives for 25- and 100-year protection Ignored inlet capacity

8 Project Overview Design Phase Design of upstream pipe system improvements Hydraulic analysis and routing in EPA SWMM 5.0 Dynamic model solves full St. Venant equations, which account for momentum and acceleration terms ignored in steady state analysis User input hydrographs from HMS Modeled both conduits, streets, and flow splitting simultaneously Ignored inlet capacity

9 Kaufman Outfall

10 Flow Comparison at Kaufman Outfall Peak Discharge at Kaufman (Q p ) Return Period (yr) HMS SWMM % Decrease

11 Kaufman Outfall (100-year) HMS SWMM Q p = 3520 cfs Q p = 3183 cfs (10% reduction) Q (cfs) Time (min)

12 Kaufman Outfall (25-year) HMS SWMM 3000 Q p = 2604 cfs 2500 Q p = 2391 cfs (8% reduction) 2000 Q (cfs) Time (min)

13 Kaufman Outfall (5-year) HMS SWMM Q p = 1680 cfs Q p = 1346 cfs (20% reduction) 1200 Q (cfs) Time (min)

14 Kaufman Outfall (2-year) HMS SWMM 1500 Q p = 1213 cfs 1200 Q p = 1063 cfs (12% reduction) 900 Q (cfs) Time (min)

15 Practical Results Cost savings! Structure/Link Study Design Cost Savings (%) Hydraulic Highway (900 lf) 2-9 x6 2-8 x5 26 Realign existing 2-8 x42 x4 (500 lf) 2-8 x4 1-8 x4 50 Junction Boxes

16 Phillips Street Bridge Improvements Phillips Street (670-ft downstream of Kaufman Outfall) Reduced peak 7% DART (1200-ft downstream of Kaufman Outfall) Reduced peak 10%

17 HEC-HMS Model Update Step 1: From existing conditions SWMM model, obtain hydrograph at pipe system outfall (Kaufman) Step 2: In HMS, replace basins C1-C8 with hydrograph from SWMM Step 3: Compare flows downstream Location (Distance 100-yr Peak Discharge (Q p ) from Kaufman, ft) HMS SWMM % Decrease Kaufman Phillips (670) DART (1200) Spring Valley (2790)

18 Phillips - 670' Downstream (100-year) HMS SWMM 4000 Q p = 3625 cfs 3000 Q p = 3362 cfs (7% reduction) Q (cfs) Time (min)

19 DART ' Downstream (100-year) HMS SWMM Q p = 4825 cfs Q p = 4332 cfs (10% reduction) 3000 Q (cfs) Time (min)

20 Spring Valley ' Downstream (100-year) HMS SWMM 6000 Q p = 5071 cfs Q p = 4512 cfs (11% reduction) Q (cfs) Time (min)

21 Other modeling considerations Design Time & Cost (StormCAD vs. SWMM) Existing condition modeling more intense in SWMM due to an increased level of input Proposed condition modeling effort drastically reduced due to elimination of manual iteration in flow splitting Increased accuracy level of routing in large pipes with SWMM as opposed to HMS (none in StormCAD!) Inlet analysis weirs in EPA SWMM are sometimes unstable leading to model reliability concerns. Client/Audience consideration