Eel Point Road Restoration and Resilience

 

Sponsor: Linda Loring Nature Foundation
Sponsor Liaison: Sarah T. Bois, Seth I. Engelbourg, Kathryn K. Pochman
Student Team: Anthony DeMarco, Jonathan Pantojas, Kelly Pritchard, Madison Reiber
Abstract: The goal of this project was to research, identify, and recommend solutions to mitigate the effects of continued flooding and erosion on Eel Point Road (EPR) on Linda Loring Nature Foundation (LLNF) property. We assessed and documented EPR conditions, identified EPR users, and surveyed and interviewed key personnel. Then, we integrated our research with pre-existing data from the LLNF and recommended both near- and long-term solutions for flooding and erosion control to the LLNF. We determined that regular maintenance is required in identified problem areas on EPR.
Link:

Final Report: LLNF_Report_1215.pdf

Final Presentation: LLNF_FinalPrestn_1212.pptx

Photographs: LLNF_Photographs.zip

Trail Camera Data: LLNF_TrailCameraData.xlsx

Survey Data: LLNF_SurveyResults.xlsx

Executive Summary

Introduction

The Linda Loring Nature Foundation (LLNF) is a 275-acre land trust and conservation foundation located on Nantucket. It was established in 1999 by Linda Loring and became operational in 2007 with a mission to preserve the natural landscape of Nantucket (“History”). The Linda Loring Nature Foundation building, located on 110 Eel Point Road (EPR), is dedicated to preserving and researching the biological diversity of their property and in prioritizing its resiliency. This includes monitoring rare and endangered species and the control of invasive species. In addition, weather data is collected through weather stations on the property. The LLNF provides education for the Nantucket community through academic and community programs, workshops, and special events (“Education”).

The only point of vehicle access to the LLNF property is the unpaved section of EPR. The road is prone to flooding and heavy erosion that alters its shape, and by 2070, EPR is expected to experience up to 6 inches of flooding daily during high tides (“Nantucket Coastal” 4).  The flooding and erosion of EPR has resulted in the fragmentation of habitat protected by the LLNF; if the flooding and erosion problems are not addressed, habitat loss and damage will increase (S. Bois, personal communication). Access to the LLNF and surrounding properties may become limited.

Background

Unpaved roads are composed of three structural layers: the road surface, gravel, and subgrade (Shtayat et al. 632) The surface and gravel layers are often composed of stone, rock, or sand, while the subgrade is formed from compacted native soil (ibid).  These layers are shaped to form the road crown, which allows water to drain off the road surface (“Crown & Cross-Slope” 1).

Unsurfaced roads experience seven types of distress that impact their functionality: improper cross section, inadequate roadside drainage, corrugations, dust, potholes, ruts, and loose aggregates (Saha & Ksaibati 4). The erosion of unpaved roads is affected by the composition of the surface and subgrade, as well as from traffic flow across the road surface (Alvis et al. 183-188). If the surface or subgrade layers are improperly constructed, the rate of erosion on the road increases (ibid). The impact and flow of rainwater across the road surface also contributes to the erosion of unpaved roads (Ngezahayo et al. 2-3). The rise in relative sea level (RSL) is projected to increase the effects of water-based erosion: flooding frequencies are expected to increase by 5 times their current amount by 2050, from 0.04 severe flooding events per year to 0.2 severe flooding events per year (“Sea Level Rise Scenarios” xiii).

To directly address distresses on unpaved road surfaces, blading and reconstructive grading are used. Blading is the practice of smoothing the road surface by redistributing loose aggregates, while reconstructive grading involves the removal, redistribution, and compaction of the road surface (Kearley 3-4). Additionally, multiple structures can be installed as part of an unpaved road to mitigate the effects of flooding and erosion on the road. These structures include ditches, culverts, outlet structures, and bank stabilizations (Kearley 11-24).

Eel Point Road (EPR) is a partially paved road on the west end of Nantucket, with access to points of interest including Eel Point, Dionis Beach, the Linda Loring Nature Foundation (LLNF), and 40th Pole Beach. Erosion on EPR is caused by multiple factors, including heavy summer traffic, construction vehicle use, and repeated grading of the road (S. Bois, personal communication). Additionally, rising sea levels may result in up to 6 inches of daily flooding on EPR by 2070 (“Nantucket Coastal” 4). Increased volumes and frequencies of flooding on EPR are expected to increase the erosion of EPR (S. Bois, personal communication).

Goals and Methods

The goal of this project was to research, identify, and recommend solutions to mitigate the effects of continued flooding and erosion of Eel Point Road (EPR) on Linda Loring Nature Foundation (LLNF) property in both the near and long term. To achieve this goal, the research team developed the following objectives:

  1. Assess and document current conditions on EPR[1] via road surface condition indexing, photography, and qualitative observations of the road.
  2. Identify users of EPR by analyzing the composition of vehicle traffic.
  3. Survey and interview key personnel how road conditions are perceived by the community.
  4. Assess and document how road conditions impact the usability of EPR.
  5. Integrate research with pre-existing data from the Linda Loring Nature Foundation (LLNF) via updating GIS mapping and documentation of research data.
  6. Recommend flooding and erosion control, and maintenance solutions implementable by the LLNF on EPR over varying timelines based on research data.

To achieve this goal, the research team assessed current conditions on EPR through photography and the Unsurfaced Road Condition Index (URCI). Vehicle traffic composition on EPR was determined through a trail camera placed on LLNF property that recorded the types of vehicles used on EPR over a two-week period. Through social media, flyers, e-mail, and local news, an online survey was distributed to identify user demographics of EPR and how these users perceived road conditions on EPR.  A series of 15-minute targeted interviews were conducted with town employees, first responders, fishers, and residents to learn about how specific road conditions on EPR impacted its usability. The data collected from these methods were then integrated with GIS data from the LLNF and public databases to fully visualize road conditions on EPR. Finally, this data was used to produce and recommend both short- and long-term erosion and flooding control solutions for EPR to the LLNF that could be applied across multiple potential timelines.

Results

In assessing the current condition of EPR, determining the composition of vehicle traffic on EPR, surveying and interviewing EPR users, and integrating our data with data from the LLNF and public databases, the research team learned the following:

  • The most severe distresses on EPR are improper cross sections, corrugations, and loose aggregates.
  • The main form of vehicle traffic on EPR is from passenger vehicles. During the study window in early November, EPR experienced a traffic volume of approximately 81 vehicles per day, with peak traffic occurring at 11:00 AM.
  • Over 50% of survey respondents rated the road condition and maintenance of EPR poorly or very poorly. Of the respondents familiar with EPR, 55% rated its condition as being worse than other unpaved roads on Nantucket.
  • The conditions on EPR negatively affected resident and first responder access to locations on the road. Interviewees expressed interest in regrading EPR and establishing a consistent road height and width.
  • Two sections of EPR are projected to experience severe potential flooding yearly by 2070. The GIS map of EPR allowed the research team to identify sections of EPR at risk for future flooding and erosion and to target road repair and maintenance solutions to specific sections of EPR.

Recommendations

The research team recommends that the Linda Loring Nature Foundation (LLNF) perform the following actions on EPR to reduce the effects of flooding and erosion of the road on foundation property:

  • Regrade Eel Point Road to address potholes, corrugations, ruts, and loose aggregates that impact the usability of EPR. This will also allow water to drain from the road surface into the surrounding environment.
  • Install an artificial wetland area in sections of EPR to hold large amounts of water runoff from storms and reduce the effects of flooding.
  • Establish a consistent road width on Eel Point Road to prevent traffic hazards.

The research team recommends that the LLNF perform the following actions on EPR to supplement the recommendations listed above:

  • Establish a road path on Eel Point Road to create a set layout of the road.
  • Implement a civic association to address maintenance, funding, and organization of the repairs on Eel Point Road.
  • Install warning signs on Eel Point Road to inform EPR users of current road conditions.

Future research concerning EPR should be conducted in the following areas:

  • Conduct additional trail camera studies to determine how frequently EPR is used during different seasons.
  • Survey abutters of Eel Point Road to determine which road repair and maintenance solutions should be implemented.
  • Continue indexing the conditions of Eel Point Road annually by utilizing the Unsurfaced Road Condition Index (URCI).

[1] From the area of 69 Eel Point Road to the 40th Pole Beach parking lot: this is the section of EPR bordering LLNF property and is a private road.