EFFECTS OF SEA-LEVEL AND GROUNDWATER RISE IN COASTAL NEW HAMPSHIRE. D. Schiff, J.F. Knott, J. Jacobs, J. Daniel August 2017

Transcription

1 EFFECTS OF SEA-LEVEL AND GROUNDWATER RISE IN COASTAL NEW HAMPSHIRE D. Schiff, J.F. Knott, J. Jacobs, J. Daniel August 2017

2 PURPOSE 2 Coastal communities are threatened by SLR global sea levels projected to rise 2 m by 2100 Groundwater rise due to SLR warrants further study Can occur in areas already affected by SLR Could possibly double the size of upland areas affected by SLR Affects freshwater wetlands, up to 4 km inland, which has not been explored by previous surface-water inundation studies Findings may help Rockingham Planning Commission and NHDES identify vulnerable ecosystems and offer guidance in conservation efforts for mid-century and end-of-century scenarios. Source: National Climate Assessment (2012), NOAA.

3 GOALS 3 Map surface-water inundation at mean sea level Map changes in surface-water inundation from 0.8 m and 2.0 m SLR Compare to Sea Level Affecting Marshes Model (SLAMM) findings Calculate and map groundwater rise Map current freshwater wetlands at MSL Map where new wetlands may form due to GWR Map where existing wetlands may experience increased water depth due to GWR Map wetland type conversions due to increased water depth Assess possible effects of SLR and GWR on vegetation and fisheries

4 STUDY AREA 4

5 NH Seacoast Region 5 Rockingham County 13 communities, 88K residents Hydrologically diverse and complex Great Bay Estuary, Piscataqua Estuary, Hampton-Seabrook Estuary Sea-level Rise (SLR) From 1927 to 2001, region experienced 13.5 cm SLR By 2100, projected 1.2 to 2.0 m SLR (NOAA) Study considered two SLR scenarios: 0.8 m by 2060 and 2.0 m by 2100

6 ECOSYSTEMS 6 Estuarine Eelgrass Shellfish Anadromous species Freshwater Forested, scrub wetland Wet meadow Shallow emergent Deep emergent Aquatic bench

7 METHODOLOGY 7

8 8 OVERVIEW NOAA surface-water inundation mapping MODFLOW 2005 output (J.F. Knott 2017b) LiDAR to DEM Surface-water inundation, groundwater rise, groundwater inundation, wetland change Spatial resolution 2 m - DEM 10 m - raster calculations 90 m - GW piezometric head raster Town by town analysis Comparison to SLAMM and NWI

9 LIDAR TO HYDRO-FLATTENED DEM 9

10 SURFACE- WATER INUNDATION 10

11 11 GROUNDWATER RISE MODFLOW 2005 output (J.F. Knott 2017b) GW piezometric head data converted to raster GW table and GWR calculated using map algebra

12 FINDINGS 12

13 SWI VS. SLAMM 13

14 FRESHWATER WETLAND EXPANSION AND INCREASED WATER-DEPTH 14

15 FRESHWATER WETLAND CONVERSION FROM MSL TO 2.0 M SLR 15 Table 3. GWR due to 2.0 m SLR effect on existing wetland depth classification km 2 of wetland type shift as GWR causes depth expansion GWR mean (m) 2.0 SLR GWR max (m) 2.0 m SLR Wet Meadow to SE, DE, AB, OW Shallow Emergent to DE, AB, OW Deep Emergent to AB, OW Aquatic Bench to Open Water Greenland Hampton Hampton Falls Newington Portsmouth Rye Seabrook Note: Wet meadow is 0-15 cm (0-6 in) of water inundation; shallow emergent is cm (6-18 in); deep emergent is cm (18-36 in); aquatic bench is 91 cm- 2.1 m (3-7 ft); and open water is greater than 2.1 m (7 ft).

16 CONCLUSION 16

17 17 OUR STUDY Established methodology for mapping wetland change due to GWR Applied NOAA surface water mapping to coastal NH Modeled possible freshwater wetland expansion for mid-century and end-of-century SLR projections Identifies potential wetland conversion for RPC and NHDES conservation efforts RECOMMENDATIONS FOR FUTURE STUDIES MHHW to capture worst-case scenario Saltwater intrusion modeling DEM improvement as LiDAR becomes available

18 18 VISUAL CITATIONS Images: SLR Projections, NOAA, ArcScene inundation video, Schiff et al., Great Bay Shells, Schiff, 2017 NH Wetland, Schiff, Methodology flow chart, Schiff et al., Rock formations in Great Bay, Schiff, Maps: NH Seacoast, Schiff et al., LiDAR, Schiff et al., Hydro-flattened DEM, Schiff et al., GW Table, Schiff et al., GWR 0.8 m SLR, Schiff et al., GWR 2.0 m SLR, Schiff et al., SWI vs. SLAMM, Schiff et al., Wetland expansion-aerial imagery, Schiff et al., Wetland expansion-gray imagery, Schiff et al., 2017.