SWAP Risk Informed Methods for Stormwater Assessment and Prioritization

Transcription

1 SWAP Risk Informed Methods for Stormwater Assessment and Prioritization Sara Hillegas Woida, Hydraulic Engineer US Army Corps of Engineers, Pittsburgh Thomas Maier, Biologist/Planner US Army Corps of Engineers, Pittsburgh March 2017 US Army Corps of Engineers

2 Topics Study purpose & pilot projects Field reconnaissance & data collection Hydrologic & hydraulic analysis Prioritizing sites putting the tool to use Lessons Learned Challenges & Opportunities 2

3 Study Purpose Partnership with the Southwestern Pennsylvania Commission (SPC) Planning Assistance to States (PAS) Pgm USACE Pittsburgh District GOALS: 1. GIS inventory, field survey, analyze municipal stormwater infrastructure (culverts, small bridges) 2. Prioritize areas for future flood response and infrastructure management 3. Extend the methodology to other regional entities 3

4 Pilot Projects Elizabeth Township, Allegheny County 15 miles southeast of Pittsburgh, between Monongahela and Youghiogheny rivers 59 potential sites 30 sites met pilot study guidelines, with a total of 40 culverts Burrell Township, Indiana County 40 miles east of Pittsburgh, between the Conemaugh River and Blacklick Creek 78 potential sites 36 sites met pilot study guidelines, with a total of 38 culverts Both pilot project sites have experienced significant damages from recent flash flood events Increasing frequency and intensity of rainfall events in the future?(ref: 2017 ORB Climate Change Study) 4

5 Pilot Projects 5

6 Field Reconnaissance GIS Inventory Local Asset Management (LAM) sites Potential locations (NHD + street layer) Field Reconnaissance/Survey Sites limited to: Culverts less than 4 feet in diameter Total opening width < 20 feet Hard stream bottom No superstructure or abutments Municipal roads Defined natural stream (USGS blue line) 6

7 Field Data Sheet Survey Survey-grade GPS Hand level Site photos QA/QC GIS analysis Data review Data Collection Sites with potential errors were revisited Erin Kepple-Adams, SPC Water Resource Manager (11/24/15) Sites where inlet or outlet could not be located were removed from the inventory 7

8 Hydrologic Analysis US Geological Survey (USGS) StreamStats Web-based GIS application using USGS regression equations for ungaged streams Discharge-frequency (RI Q ) Peak flow statistics 2, 5, 10, 50, 100 & 500 year recurrence interval floods Corresponds to the 50, 20, 10, 2, 1, 0.2% ACE 8

9 Hydrologic Analysis 9

10 Hydrologic Analysis USGS StreamStats Flow statistics based on Drainage area Mean basin elevation Percent carbonate, urban, storage Additional Output Basin characteristics (slope, centroid, land cover) GIS shapefiles Limitations Minimum drainage area of 2.33 mi 2 Flows based on 2008 report USGS Scientific Investigations Report Historic observations (assumes stationarity) 10

11 Hydraulic Analysis Federal Highway Administration (FHWA) HY-8 Culvert Hydraulic Analysis Program Automated culvert hydraulic computations Input site characteristics (size, shape, slope) Headwater elevation = Roadway crest Solves for Discharge Capacity (Q C ) Sites with multiple culverts were aggregated Hydraulic failure assumed when roadway is overtopped 11

12 Hydraulic Analysis FHWA HY-8 SCREENSHOT 12

13 Hydraulic Analysis Discharge Capacity (Q C ) + Discharge Frequency (RI Q ) curve Capacity Frequency (RI C ) Q C from FHWA HY-8 (cfs) RI Q from USGS StreamStats (years) RI C = capacity recurrence interval (years), based on the overtopping discharge capacity 13

14 Burrell Township Site #42 Discharge Capacity = 284 cfs Capacity Frequency = 430 years 14

15 Prioritization Scheme Hydraulic Adequacy (HA) Compare Capacity Frequency (RI C ) to applicable design guidelines PennDOT Flood Selection Guidelines Based on Functional Classification Minimum Recurrence Intervals Functional Classification Minimum Recurrence Interval (years) Interstate and Limited HA Access < PADOT Highways = Poor50 Principal Arterial System 50 Minor Arterial System 25 HA > 50 years = Good Rural Collector System, Major 25 Other Collector Systems 10 Local Road and Street Systems 10 PADOT < HA < 50 years = Moderate 15

16 Prioritization Scheme 16

17 Results RI C = 844 years RI C = 0.4 years Burrell Township Case Study Additional considerations: Traffic volume Physical condition Surrounding land use Observed performance 17

18 Lessons Learned Safety First: Travel in pairs, wear PPE Training Data collection Hydraulic definitions Bridge vs. Culvert Natural channels GPS issues Understand GIS data limitations 18

19 Challenges & Opportunities Challenges to Success Feedback loop Monitoring Networking Opportunities to Improve Structural integrity/adequacy Asset management Climate change Flood response with increasing rainfall intensity Fish passage considerations Act Monitor Feedback Loop Modify Assess 19

20 Asset Management in a Changing World ~from Groisman et al Contemporary Changes of the Hydrological Cycle Trends Derived from In Situ Observations Closed, over-topped roads washed-out roads 20

21 Asset Management in a Changing World What s increasing rain intensity? A warmer atmosphere s capacity to hold more moisture & energy. Projected number of days/year with maximum temps greater than 90 F averaged between , compared to (Historical Climate) assuming continued increases in global emissions (A2) and substantial reductions in future emissions (B1). Take-away: even under the reduced emissions model, we may anticipate warmer temps w/ an increase in rainfall intensity. ~ from NOAA NCDC/CICS-NC 21

22 Asset Management in a Changing World Under-sized or otherwise insufficient crossings for future rainfall events may be indicated by current: Outlet drops with scour pools high velocities, turbulence, erosion, debris blockages, and 22

23 Asset Management in a Changing World or by fish crossing the road! Under-sized crossings are also common problems for fish (& wildlife) passage, with longitudinal connectivity an increasing concern for a warmer future. 23

24 Asset Management & Fish Passage? 24

25 Future Asset Management, including Potential Fish (& Wildlife) Passage Well-designed crossings include: Large size for high flows Open-arch design, preserving the natural stream channel Openness ratio > 0.5 m Crossing span, maintaining dry passage for wildlife Water depth & velocity comparable to upstream and downstream Natural substrates, creating good conditions for stream dwelling animals ~from Massachusetts Steam Crossings Handbook 25

26 Potential Fish & Wildlife Passage? Well-designed box culvert (The below are not Brook Trout!) Massachusetts Steam Crossings Handbook, at: North Atlantic Aquatic Connectivity Collaborative, at: 26

27 Future Asset Management North Atlantic Aquatic Connectivity Collaborative (NAACC) Protocols & training for assessing road-stream crossings Regional database for field data Identify high priority bridges & culverts for upgrade and replacement Roadsoft Roadway asset management system Michigan Department of Transportation Integrates local roads into the State database 27

28 Summary Planning Assistance to States (PAS) cost share program Partnership with the Southwest Pennsylvania Commission (SPC) Field reconnaissance, survey, and data collection H&H analysis using readily available tools Risk-informed approach to prioritize storm water infrastructure improvement Improve and extend the methods to other municipalities 28

29 Questions? Sara Woida, Tom Maier, Michael Debes, 29

30 Authorization & Program Information Continuing Authorities Programs (CAP) -- can be conducted without obtaining a project-specific study or construction authorization (above), or appropriations. Other Pittsburgh District Authorities requiring only projectspecific appropriations 30

31 Continuing Authority Programs CAP Eligible Activities MAXIMUM Federal Construction Cost Share (C/S) Per Project Federal Limit Program Federal Limit (annual) Sec. 14 Streambank and shoreline erosion of public works and nonprofit services 65% $5M $20M Sec. 107 Navigation improvements 50% for recreational-- varies for navigation Sec. 111 Prevention/mitigation of shore damage caused by Federal navigation projects C/S same proportion as original project* $10M $50M $10M N/A Sec. 204 Beneficial use of dredged material 65% N/A $50M Sec. 205 Flood control 65% $10M $55M Sec. 206 Aquatic ecosystem restoration 65% $10M $50M Sec. 208 Sec Obstruction removal & clearing channels for flood control Project modifications for improvement of the environment 65% $0.5M $7.5M 75% $10M $40M 31

32 Other Pittsburgh District Authorities Authority Eligible Activities MAXIMUM Federal Construction Cost Share (C/S) Per Project Federal Limit Program Federal Limit (annual) Planning Assistance to States Technical assistance in water resource planning on a regional and comprehensive scope. 50% $5M annually per state $30M Floodplain Management Services (FPMS) Sec. 219 Environmental Infrastructure Sec. 313 South Central Pennsylvania Environment Infrastructure Technical assistance with flood and floodplain issues Resource protection and development of waste water treatment, water supply storage, etc. Same as Sec. 219, except limited to SW & South-Central PA counties (including Westmoreland County) 100% N/A $50M 75% N/A $30M 75% N/A $200M 32

33 Bridge vs. Culvert 33