Assessing the Risk of 100-year Freshwater Floods in the Lamprey River Watershed of New Hampshire Resulting from Changes in Climate and Land Use

Transcription

1 Assessing the Risk of 100-year Freshwater Floods in the Lamprey River Watershed of New Hampshire Resulting from Changes in Climate and Land Use Presented by: Ann Scholz, PE, CPSWQ Advisor: Dr. Robert Roseen, PE, D.WRE Funding: The Cooperative Institute for Coastal and Estuarine Environmental Technology Principal Investigator: Cameron Wake Technical Support : Robert Roseen, PE, PhD, Thomas Ballestero, PE, PhD, Michael Simpson Newmarket, NH April 2007

2 Outline Project Objectives Importance of Research Lamprey River/Watershed Methodology Research Status 2

3 Project Objectives Construct a current hydrologic and hydraulic model for the watershed and river respectively Improve the existing information regarding base flood elevations and flood risk areas Assess the effect of future development and increased precipitation due to climate change Present land use management strategies to mitigate runoff volumes 3

4 15 Highest Events Daily Discharges on Lamprey River near Newmarket Rank Date Discharge (cfs) 1 16 May May Apr Apr Apr Apr Apr Mar Mar Mar Oct Oct May Mar Mar Apr Mar Apr Feb Mar Apr Jun Jun Mar Apr Of 15 largest events since 1934: 11 have occurred in last 25 years 10 have occurred in last 15 years 7 have occurred in last 5 years Source: 4

5 FEMA Requirements for Redelineation Hydrologic Analysis: o Bulletin 17B for gaged streams Effective Model 1935 through 1987 Q 100 = 7,300 cfs o Criteria for revised hydrologic analysis Statistically Significance (68-percent confidence interval) L 0.01,0.68 = 6,886 cfs H 0.01,0.68 = 7,834 cfs 75 yr record Q 100 = 9,411 cfs Statistically Significant 5

6 Change to Base Flood Elevation and Spatial Extents 6

7 Lamprey River Watershed 7

8 Lamprey River Studies Summary of Town Studies Community Town FIS Date Study performed by Completed Raymond October 15, 1981 SCS September 1979 April 15, 1992 Rivers Engineering Corp. October 1989 May 2, 1995 Roald Haestad, Inc. March 1993 Epping October 15, 1981 SCS September 1979 Lee No published study available Durham May 3, 1990 SCS September 1987 August 23, 2001 USGS April 1998 Newmarket May 2, 1991 USGS August

9 GIS Data Assembly Terrain Digital Elevation Model (DEM) Watershed(s) Hydrologic Unit Code (HUC) Transportation data and water features Digital Line Graph (DLG) Stream Networks River Reach Files (RF)/National Hydrography Dataset (NHD) Streamflow Gage Data Locations Latitude/Longitude Aerial Background Digital Orthophoto Quarter Quads (DOQQ) Soil type data Soil Surveys Geographic Data Base (SSURGO) State Soil Geographic Data Base (STATSGO) Land Use Cover USGS Land Use Land Cover (LULC) State/Municipal GIS 9

10 Hydrology Overview Standard Hydrologic Grid Hydrologic Rainfall Analysis Project HEC GeoHMS (ArcHydro Tools) to process DEM Delineate Watershed and Sub watershed GIS Preprocessed Spatial Hydrology Data Base DEM Reconditioning Runoff Parameters Stream Network HEC HMS Input File 10

11 Watershed Hydrologic Analysis W1380 W7060 W6510 Subbasin Area (mi2) W W W W W W W W W W W Total W7920 W8600 W8380 W11020 W8590 W11900 W10910 W

12 Land Use Within the Watershed Subbasin CN W W W W W W W W W W W W6510 W1380 W7060 W7920 W8600 W8380 W8590 W11020 W11900 W10910 W

13 UNH Hydrology Model Rainfall o Depth-duration-frequency TP-40 Rainfall Frequency Atlas of the United States is being used for effective conditions Northeast Regional Climate Center Atlas for Extreme Precipitation. FEMA guidelines for redelineation indicate the need to use current depth duration frequency data. 13

14 Calibrating the Watershed Calibration: o April ,590 cfs, Precipitation 7.65 in o March ,550 cfs, Precipitation 7.02 in Optimization parameters: o Manning s n o Lag Time Simulated for o Time to peak o Runoff volume o Peak flow 14

15 Calibrating the Watershed 15

16 1 6

17 Calibrating the Watershed 17

18 Calibrating the Watershed Hydrology Model Calculated flood flow for the gaged 183 sq.mi. watershed Results of calibrated model run for current land use (2005) using TP-40 rainfall. Q 100, TP-40 = 7,580 cfs vs. Q 100, FIS = 7,300 cfs Results of calibrated model run for current land use (2005) using NRCC Atlas rainfall. Q 100, CA = 10,649 cfs 68-percent confidence interval of gaging station estimate for data from , Q 100, LP3 = 9,411 cfs L 0.01,0.68 = 8,862 cfs H 0.01,0.68 = 10,040 cfs 18

19 Hydrologic Studies Project Models Rainfall Rates and Global Change Model Scenario Land Use Conditions Effective Updated Climate Period Climate Period TP-40 NRCC NRCC A1F1 (HI) B1 (LO) Current (2005) X X Build-out X X X LID/Build-out X X X NRCC Northeast Regional Climate Center TP-40 Technical Paper 40 A1F1 (HI) - Continuation of growth B1 - Stabilizing CO 2 concentrations 19

20 Hydraulic Overview HEC GeoRAS (ArcView ) Create Stream Stationing and Reaches GIS Preprocessed Spatial Hydrology Data Base Create Stream Cross Sections Extract Elevation Data HEC RAS Input File RAS Mapping 20

21 Cross Section A10 East 265, 283 Wadleigh Falls Road Lee, NH 2

22 FEMA Library Historic Data and Development of Floodplain Hydraulics Model 22

23 Hydraulics Model Cross Sections Summary of Cross Section Data Source Source Number FEMA FIS Backup Data 111 Duplicates 19 Surveyed 12 NHDOT/Consultants 34 GIS 44 Total 220 FIS sections were duplicated as needed to provide immediate sections up and downstream of bridges No backup data available for Lee Projects included additional sections supplementing FIS sections Improved modeling in RT108 corridor and tributaries 23

24 Hydraulics Model Structural Data Summary of Bridge Structure Source for the Lamprey River Community Station Road Name Data Source Raymond Dudley Road Raymond Road (RT 27) Langford Road Main Street Epping Street B&M Railroad Freetown Road (RT 107) Prescott Road Epping State Route 101 Electronic WSP2 files from Roald Haestad, Inc. March Epping Road (RT 27) Electronic HEC RAS files from NHDOT, Blake Road Main Street (Plummer) As built drawings from NHDOT, dates vary Mill Street Calef Hwy (RT 125) Electronic HEC RAS files from NHDOT, Hedding Road (RT 87) WSPRO print out and As built from NHDOT, 2000 Lee Wadleigh Falls Road Lee Hook Road As built drawings from NHDOT, dates vary Durham Wiswall Road Electronic HEC RAS files from CLD Consulting, Packer's Falls Road Newmarket 1602 RT 108 FEMA FIS Backup Data Summary of Bridge Structure Source for the RT108 Corridor Watercourse Station Road Name Data Source Floodplain 71 Newmarket Road (RT 108) Survey drawings from NHDOT, 2010 Hamil Brook 1040 Newmarket Road (RT 108) Longmarsh Brook 4182 Bedard Road Longmarsh Brook 1703 Longmarsh Road FEMA FIS Backup Data Longmarsh Brook 275 Tote Road 24

25 Hydraulics Model Dam and In-line Structural Data Summary of In line Structure Source for the Lamprey River Community Station Road Name Data Source Epping Bunker Pond Dam Electronic HEC RAS files from NHDOT Lee Wadleigh Falls Dam Land Records Durham Wiswall Dam Electronic HEC RAS files from CLD Consulting Engineers Newmarket 1286 Coffee Sluice Newmarket 1164 Macallen Dam Electronic HEC RAS files from Wright Pierce NHDES Dam Management studying removal of Bunker Pond dam Wiswall bridge has been replaced and downstream dam replacement in near future Macallen Dam recently inspected per NHDES request Spillway dimensions and layout, elevation field verified 25

26 HEC-GeoRAS Hydraulic Analysis 26

27 Hydraulics Model Boundary Conditions o FIS backup data (effective model flows) o Rating Curve for Macallen Dam o Normal Depth for Hamil Brook 27

28 Hydraulics Model Diverted Flow Effective Model Assumed 20-percent of flood flow bypassed to the Oyster River watershed HEC-RAS Junction at Lamprey River and RT 108 floodplain corridor Reach River Sta Profile W.S. Elev E.G. Elev Q Total Downstream (ft) (ft) (cfs) EGL Diff. USaltRT SCS 100 YR , USaltRT Apr , USaltRT Mar , Junction: RT108 FP Optim. % Bypass DS RT108 FP 8890 SCS 100 YR , % DS RT108 FP Apr , % DS RT108 FP Mar , % OR_Bypass 6377 SCS 100 YR , % OR_Bypass Apr % OR_Bypass Mar , % 28

29 Hydraulics Model Results for RT108

30 Hydraulics Model Results for RT108 NRCC 100-YR WSE = April 2007 WSE = March 2010 WSE =33.58 FIS WSE = 33.0 Observed WSE: April March

31 Hydraulics Model Results for upstream of Mill Street, Epping SCS 100-YR WSE = April 2007 WSE = FIS WSE = Observed WSE: April

32 Hydraulics Model Rating curve comparisons at USGS gage 32

33 Hydraulics Model General Profile Plot 220 Lamprey River EGL Profile Plot Elevation (ft) Reach Length (ft) HEC-RAS FIS 33

34 Hydraulics Model General Profile Plot Longmarsh Brook to Hamil Brook Profile Plot Elevation (ft) Reach Length (ft) HEC-RAS FIS 34

35 Watershed Buildout 35

36 LID Buildout Commercial Zoning 36

37 LID Buildout One Acre Residential 37

38 Research Status Model buildout scenarios for 2050 and 2085 with traditional and low impact design features Run hydraulic model with flood flows Map spatial extent of flood areas 38

39 Acknowledgments Robert Roseen, Director, UNH Stormwater Center Thomas Ballestero, Department of Civil Engineering, UNH Cameron Wake, Institute for the Study of Earth, Oceans and Space, UNH Steve Miller, Great Bay National Estuarine Research Reserve Kathy Mills, Great Bay National Estuarine Research Reserve Fay Rubin, Institute for the Study of Earth, Oceans and Space, UNH Michael Simpson, Antioch University New England Lisa Townson and Julia Peterson, UNH Cooperative Extension Cliff Sinnott, Rockingham Planning Commission 39

40 Thank you for your time. Questions?