Are Flood Stages Rising? Our Fault or Mother Nature s?!

Transcription

1 Are Flood Stages Rising? Our Fault or Mother Nature s?! ASFPM National Conference June 4, 2014 Presented by: Siavash Beik, PE, CFM, D.WRE Peggy Shepherd, P.E., CFM Christopher B. Burke Engineering, LLC

2 Flooding is now more frequent and more severe! It s because of that new bridge restricting flow! No, it s just climate change! No, it s all the impervious area at that new industrial complex!

3 Is Flooding Getting Worse?

4 Is Flooding Getting Worse? What factors go into making a flood?

5 Is Flooding Getting Worse? What factors go into making a flood? What s happening with these factors?

6 Is Flooding Getting Worse? What factors go into making a flood? What s happening with these factors? What are the implications?

7 Is Flooding Getting Worse? What factors go into making a flood? What s happening with these factors? What are the implications? Can We Do Anything?

8 What factors go into making a flood? 1) Rainfall how much and how fast small amounts, slow large amounts, fast

9 Courtesy of landscapeforlife.org What factors go into making a flood? 2) Land use, soil type, surface slope - how fast does the ground send how much of the rainfall to the streams -or- Wooded, pervious, flat concrete, no exposed soil, steep

10 What factors go into making a flood? 3) Flow Path how open is it? Low grasses in channel & overbank, high capacity bridges Low large girder bridges, levees and other floodplain encroachment

11 What factors go into making a flood? 1) Rainfall 2) Surface, soil & slope 3) Flow Path Best Case Scenario Worst Case Scenario

12 Is Flooding Getting Worse? What factors go into making a flood? What s happening with these factors? 1) Rainfall 2) Land use, soil, slopes 3) Flow path

13 What s Happening to: 1) Rainfall? Trend line shows increase

14 What s Happening: 2) Because of Land Use? Impacts of Regulated Development 100 Year Peak Discharge Release Rate requirements (detention) Prevent a small range of runoff increases from becoming peak discharge increases

15 What s Happening: 2) Because of Land Use? 2-year Discharge Increases With Watershed Development When Regulations Only Address Higher Discharges existing flood peak Impacts? predeveloped bankfull duration increased channel erosion observed

16 What s Happening: 2) Because of Land Use? Impacts of Development If Only Regulate Discharge Peaks ~10% in runoff volume (not peak discharge) for 100-yr rainfall

17 What s Happening: 3) to the Flow Path? Regulation of Floodway Only Fringe Filled Fill fringe areas (shown in green) as allowed by many community ordinances: 100-year peak flood elevations ½ - 1 ½ foot increases 500-year peak flood elevations 1-5 foot increases Development in the Floodway Fringe: May or may not impact traditional regulatory elevations Will impact observed elevations

18 What s Happening: 3) to the Flow Path? What are streams doing with the runoff they receive? Real Measured Data USGS Streamflow Gage Data WABASH RIVER AT MT CARMEL, IL current location

19 Plotting Annual Peak Gage Height vs. Discharge Plot Gage Height in feet along the Vertical Axis Plot Annual Peak Discharge in cubic feet per second along the Horizontal Axis

20 Plotting Annual Peak Gage Height vs. Discharge Sample Graph for 5 Decades of Gage Data STATION: PLEASANT RUN AT ARLINGTON AVE, INDIANAPOLIS, IN

21 ACTION MINOR MODERATE MAJOR Plotting Annual Peak Gage Height vs. Discharge Sample Graph for 5 Decades of Gage Data STATION: PLEASANT RUN AT ARLINGTON AVE, INDIANAPOLIS, IN

22 Plots of Annual Peak Discharge vs. Gage Height Showed? Four Categories of Findings: Category 1: Minor changes over time or shifting back & forth within a narrow range Category 2: Downward trend over time Category 3: Scattered but upward trend over time Category 4: Upward jump at identified point in time Samples of Categories 3 and 4 follow

23 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend STATION: KANKAKEE RIVER AT SHELBY, IN

24 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend (cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN Adding Data for 1950s

25 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend (cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN Adding Data for 1960s

26 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend (cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN Adding Data for 1970s

27 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN Adding Data for 1980s

28 ACTION Category 3: Scattered but Upward Trend (cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN MINOR MODERATE MAJOR Adding Data for 1990s

29 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend (cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN Adding Data for post 2000

30 ACTION MINOR MODERATE MAJOR Category 3: Scattered but Upward Trend (cont d.) STATION: KANKAKEE RIVER AT SHELBY, IN 2 Higher Gage Height Comparing pre 1950 s to post 2000

31 ACTION MINOR MODERATE MAJOR Category 3: Upward Trend with an Outlier STATION: WHITE RIVER AT NOBLESVILLE, IN

32 ACTION MINOR MODERATE MAJOR Category 3: Upward Trend with an Outlier (cont d.) STATION: WHITE RIVER AT NOBLESVILLE, IN Increase in Gage Height Over Time

33 ACTION MINOR MODERATE MAJOR Category 3: Upward Trend with an Outlier (cont d.) Abrupt & Unexpected Upward Shift only for 2002 Peak Discharge (backwater on 2003 which would plot almost 1 above 2005) STATION: WHITE RIVER AT NOBLESVILLE, IN Increase in Gage Height Over Time

34 ACTION MINOR MODERATE MAJOR Category 3: Upward Trend with an Outlier (cont d.) STATION: WHITE RIVER AT NOBLESVILLE, IN Due to Illegal levee downstream? - Constructed between 1998 & 2000, - breached in 2003, - removed before 2004 peak Increase in Gage Height Over Time

35 ACTION MINOR MODERATE MAJOR Category 4: Upward Jump STATION: LITTLE RIVER AT HUNTINGTON, IN Note: Deleted 1949 & 1963 which were pretty far left from anything else.

36 ACTION MINOR MODERATE MAJOR Category 4: Upward Jump (cont.) STATION: LITTLE RIVER AT HUNTINGTON, IN 3 Higher Gage Height after 1956 Note: Deleted 1949 & 1963 which were pretty far left from anything else.

37 Is Flooding Getting Worse? What factors go into making a flood? What s happening with these factors? What are the implications?

38 Q10 = 4,600 CFS Q50 = 5,600 CFS FIS Q100 = 6,000 CFS ACTION MINOR MODERATE MAJOR Implications STATION: LITTLE RIVER AT HUNTINGTON, IN 100-Year FIS Stage = 19.2 Feet Note: Deleted 1949 & 1963 which were pretty far left from anything else.

39 ACTION 100-Year FIS Q = 6,000 CFS MINOR MODERATE MAJOR Change in Elevation Produced by 100-Year Discharge of 6,000 CFS STATION: LITTLE RIVER AT HUNTINGTON, IN Post 1990 Conditions: 100-Yr. Stage Elev. = >20 Pre-1956 Conditions: 100-Yr. Stage Elev. = Yr Q once produced a stage of 17.1 but now produces a stage of over 20 Feet Note: Deleted 1949 & 1963 which were pretty far left from anything else.

40 ACTION 50-Year FIS Q = 5,600 CFS MINOR MODERATE MAJOR Change in Elevation Produced by 50-Year Discharge of 5,600 CFS STATION: LITTLE RIVER AT HUNTINGTON, IN Post 1990 Conditions: 50-Yr. Stage Elev. ~19.8 Pre-1956 Conditions: 50-Yr. Stage Elev. = Yr Q once Produced a Stage of 16.5 but now Produces a Stage of 19.8 Feet Note: Deleted 1949 & 1963 which were pretty far left from anything else.

41 ACTION 10-Year FIS Q = 4,600 CFS MINOR MODERATE MAJOR Change in Elevation Produced by 10-Year Discharge of 4,600 CFS STATION: LITTLE RIVER AT HUNTINGTON, IN Post 1990 Conditions: 10-Yr. Stage Elev. ~17.6 Pre-1956: 10-Yr. Stage Elev. ~ Yr Q once Produced a Stage of 15.1 but now Produces a Stage of 17.6 Feet (>100 yr Q s stage pre 1956) Note: Deleted 1949 & 1963 which were pretty far left from anything else.

42 Q10 = 4,600 CFS Q25 = 5,300 CFS Q50 = 5,600 CFS Q100 = 6,000 CFS ACTION MINOR MODERATE MAJOR How has Discharge Frequency for FIS 100-Year Stage Changed? STATION: LITTLE RIVER AT HUNTINGTON, IN 100-Year Stage = 19.2 Feet Stage that Previously Required > 100-Year Q now Occurs with a 25-Year Q Note: Deleted 1949 & 1963 which were pretty far left from anything else.

43 Current Discharge Frequency at FIS BFE Gage Little River at Huntington White River at Noblesville Kankakee River at Shelby Wildcat Creek near Lafayette FIS 100-yr Elevation/Stage, feet Gage s Post 2000 Peak Q at FIS E100, cfs Frequency of Gage s Post 2000 Peak Q at FIS E100 Based on FIS Discharge Tables Based on Frequency Analysis of Gage Data 746.9/19.2 5, Year 15-Year 761.2/ , Year 90-Year 640.2/12.3 5, Year 7-Year 550/ , Year 20-Year

44 ACTION MODERATE MINOR MAJOR Current BFE for FIS 100-Year Discharge Q10 = 4,600 CFS Q25 = 5,300 CFS Q50 = 5,600 CFS Q100 = 6,000 CFS Q100 updated = 7,080 CFS STATION: LITTLE RIVER AT HUNTINGTON, IN Updated 100-Year Stage = 20.2 Feet 100-Year Stage = 19.2 Feet Stage revised for updated data raises 100-Year Elevation by 1-4 feet (depending on Q/E relationship assumed at higher stages) Note: Deleted 1949 & 1963 which were pretty far left from anything else.

45 So. What s Happening to the Factors That Go Into Making a Flood? 1) RAINFALL Heavy rainfall amounts appear to be increasing 2) LAND USE Detention regulations are generally controlling peak discharges at the regulated frequencies Frequency discharges and runoff volumes that are not regulated are increasing with development 3) FLOW PATH Regulation of only the conventional floodway does not necessarily prevent increased flood stages due to development along river corridors Many stream gages are showing increasing stages for the same discharge

46 Is Flooding Getting Worse? What factors go into making a flood? What s happening with these factors? What are the implications? Can We Do Anything?

47 1) Meeting the Challenge of Higher Rainfalls Design for higher flood stages (consider future hydrology, higher freeboard, etc.) Identify potential risk areas (above and beyond minimum NFIP criteria) and stay away from them! Retrofit/floodproof critical facilities with a higher freeboard

48 2) Meeting the Challenge of Land Use Changes existing predeveloped No-Adverse-Impact Measures: Detention Ponds with accurate range of release rates to control peak discharges Retain/replace more pervious area to control runoff volumes Channel Protection Volume Retainage (through LID/Green) or extended detention to control volume

49 3) Meeting the Challenge of Impacts on the Flow Path No-Adverse-Impact Measures: Identify and protect/replace overflow paths for higher floods Require compensatory floodplain storage Accurately determine flood risk areas Some situations warrant unsteady state or 2D modeling of stream corridor (incl. auxiliary flow paths) Evaluate encroachment impacts for range of flows (2-year thru 500-year or flood of record, if larger) Don t allow encroachment if adverse impacts

50 3) Meeting the Challenge of Higher Flood Stages for the Same Discharge Enforce regulations designed to prevent increased flood stages Select freeboards sufficient to provide protection from increasing stages Remove/retrofit or don t allow encroachment if adverse impacts Gage Little River at Huntington White River at Noblesville Kankakee River at Shelby Wildcat Creek near Lafayette FIS 100-yr Elevation/Stag e, feet Gage s Post 2000 Peak Q at FIS E100, cfs Frequency of Gage s Post 2000 Peak Q at FIS E100 Based on FIS Discharge Tables Based on Frequency Analysis of Gage Data 746.9/19.2 5, Year 15-Year 761.2/ , Year 90-Year 640.2/12.3 5, Year 7-Year 550/ , Year 20-Year

51 Conclusions Evidence shows More Frequent, Higher Stages in our streams due to multiple factors Just complying with Minimum Federal and State Regulations Have/Will Not protect against increased flood stages You can do something about it by implementing No-Adverse-Impact Measures Local Governments (County, City, and Town levels) should initiate and require NAI measures appropriate for local conditions More research is needed into gaged stream reaches and watersheds to understand reasons for the observed trends USGS gages with long-term record are invaluable for understanding of flow and stage increase trends existing predeveloped

52 Questions? Siavash E. Beik, P.E., CFM, D.WRE Vice-President, Principal Engineer Phone: (317) Peggy Shepherd, P.E., CFM Senior Water Resource Engineer CHRISTOPHER B. BURKE ENGINEERING, LLC