A Geophysical and Hydrogeological Study of a Historic Site in Northeastern U.S. for Assessment of Possible of Impact of Climate Change

Historic Strawbery Banke, Portsmouth, NHStrawbery Banke is a 10 acre living history museum in the Historic District of Portsmouth on the New Hampshire coast consisting of various buildings constructed between 1690 and 1957, with gardens, galleries, and craft expositions. residing right along the coastline, this site is representative of the type of architectural stylings, building composition, and landscapes that will likely be impacted by climate change along the Northeastern Atlantic coast of US. The structures in Strawbery Banke have been restored as far as houses, gardens, etc. They are used to show visitors how people lived from the 1690’s up until the 1950’s. The area we wanted to take a closer look at was the Puddle Dock area of Strawbery Banke. It was once a shipyard when Strawbery Banke originated. Since then, it has been filled with trash and debris and is now land that people can walk on. However, there is still running water that remains subsurface. With the site being so close to the coast, the tide affects the ground-water flow as well the ground-water level. Depending on the tide and storm surge, the ground water level rises or drops.

This is a problem because when the ground-water level rises, the water overflows into the basements of these historic houses. Since the ground-water consists of saltwater, the basements are flooded with a few feet of saltwater. This saltwater decays the brick and mortar in the support beams of the house, making the house more vulnerable to permanent damage.

Methodology/AnalysisSubsurface Hydrologic AnalysisBackground: Holes were dug in Strawbery Banke approximately 4-5 feet deep in order to place water level loggers and humidity meters subsurface. Two holes were placed outside next to two buildings in Strawbery Banke. A third whole was dug in a basement to monitor flooding.Instrumentation: HOBO Water Level Loggers; Analysis:

Storm Surge AnalysisBackground: Same as above, however, the storm surge analysis is to see how much the tide is affected by storms close enough to Strawbery Banke to affect the tide.Instrumentation: HOBO Water Level Loggers; Analysis:Tidal analysis will come from the data obtained from the Water Level Loggers.

Cedric Hall, Michael Jefferson; Michael Routhier, Gopal Muluktala; Benjamin Curran

AbstractThis study reports on a project undertaken to assess the vulnerability of historic structures to the possible impacts of climate change using data collected from field geophysical survey, geospatial mapping, and a simulation to understand the hydrological conditions of the site. The study site chosen for this project is the Strawbery Banke Living History Museum, in Portsmouth, NH. Located very close to the banks of the Piscataqua River at its meeting point with the Atlantic Ocean, it consists of many buildings of historical importance dating as far back as 1690. Upstream of the river is the tidal estuary system, the Great Bay which itself is formed by a confluence of seven major rivers, making it a highly dynamic, tide-dominated body of fresh and saltwater. Strawbery Banke is representative of the type of architectural stylings, building composition, and landscapes that will likely be impacted by climate change along the northeastern Atlantic coast.

Particular attention is paid to structures and archeology surrounding Puddle Dock; a tidal inlet that once provided direct river access to Strawbery Banke (and since filled around 1900) that lies at the heart of the facility. Visual inspection of the basements and foundations of the historic structures indicate that closest to the river bank suggest that there is seepage of water at regular intervals coinciding with high tides. There is a case to be made for further examination using in situ methods so as to understand the dynamics of the freshwater-saltwater exchange including examining the seasonal variation, especially during the summer.

Results from the long term deployment of in-situ water level loggers in test wells, temperature and relative humidity sensors, and a ground penetration radar survey of the Puddle Dock, along with the detailed fine-scale elevation survey of the site are reported. Much of that data is input into an integrated model of the site that involves the simulation of fresh-water ground-water and the possible changes in them from increased ground water levels, and storm surge that are possible from the climate change.

Preliminary results indicate that at present Puddle Dock, acts as a conduit for tidal flows, albeit in a restrained manner. This can be attributed to the very unscientific way that it was filled perhaps with garbage, and other waste.

This project is in part funded by a grant from National Geographic Society's Waitt Grant program, and by NASA and The University of New Hampshire through the Research and Discover Program.

Climate Impacts on StructuresOver the course of the last 100 years the global (eustatic) mean sea level has increased at an average rate of 1 to 2 millimeters per year. The Intergovernmental Panel on Climate Change (2001) reported that this trend can be attributed to an increase in the Earth's temperature due to heightened atmospheric greenhouse gases and the subsequent glacial melting and thermal expansion of the oceans. Moreover, conservative projections report that the sea levels are further expected to rise by at least 0.3m to 0.9m from 1990 to 2100 (Barlow, 2003). In some coastal regions these factors will be exacerbated by projected localized increases in rainfall of 10 to 15% by the end of this century and a complimentary increase in the frequency of heavy-precipitation events (NECIA, 2007)

The adaptation to climate change takes a unique turn when it comes to historic structures. Unlike modern buildings, many older structures are built using materials and methods that reflect a regional connection to their specific microclimatic, geologic, geographic, and hydrologic context.

This study reports on a project undertaken to assess the vulnerability of the historic structures in the Strawbery Banke Living History Museum, in Portsmouth, NH, using data collected from field survey, geospatial mapping, and application of a hydrogeological model.

Figure 2: Maximum depth response of a GPR at Puddle Dock. The variation in physical properties of the fill can be detected from the response

Results Subsurface GPR SurveyBackground: Being that Puddle Dock was once a shipyard consisting of docking areas and piers for ships, and is now filled in, the stratigraphy is imperative to the geomorphology and ground water flow of the Puddle Dock area.Instrumentation: Ground Penetrating Radar (GPR)Analysis: GPR data will be obtained in order to get a view of the stratigraphy of Puddle Dock

Hydrologic SurveyOnce all data is obtained, MatLab analysis will be completed in order to obtain a ground water flow of Strawbery Banke.