Home » Network Narratives: Hydrologic and Hydraulic Modeling of the Assawompset Ponds Complex

Network Narratives: Hydrologic and Hydraulic Modeling of the Assawompset Ponds Complex

The Assawompset Ponds Complex (APC) is facing challenges that are all too common to the Southeast New England Region. Over the past few decades, increased development and land alterations that were made to control the flow of the Nemasket River from the APC have disrupted natural hydrological systems and degraded habitat. Adding to the impacts felt from development, climate change has only exacerbated these issues by causing more frequent flooding events.

Within Southeastern Massachusetts, approximately 15 miles north of downtown New Bedford, the Assawompset Ponds Complex covers an impressive 10,000 acres of forested lands and ponds. The complex is home to the two largest, natural freshwater bodies in Massachusetts and is the headwaters for the Nemasket River, which flows from Assawompset Pond to the Taunton River. Serving as a vital natural resource for the surrounding communities, the Assowompset Pond Complex provides public drinking water supply, wildlife habitat, and public recreation opportunities.

Drone footage of Assawompset Pond in Lakeville reveals infrastructure vulnerable to flood impacts (credit SRPEDD)

In 2020, The Southeastern Regional Planning and Economic Development District of Massachusetts (SRPEDD) applied for and was awarded technical assistance from the Southeast New England Program Network (SNEP Network). Network partners (Mass Audubon, The Nature Conservancy-Massachusetts) contracted with Horsley Witten, a consulting firm, to conduct hydrologic and hydraulic (H&H) modeling on the upper portion of the Nemasket River that drains from the Assawompset Pond Complex. The H&H modeling took place along the Nemasket River from the APC in Lakeville to just downstream of the Wareham Street Dam in Middleborough.

Danica Belknap, Senior Environmental Planner at SRPEDD explains, “The Network provided valuable modeling services, through Horsley Witten, that filled some information and data gaps to help the Assawompset Pond Complex (APC) Management Team prioritize management actions to take. As a result of the Network’s support, we now have answers about which actions will have the greatest impact on improving flow conditions in the Nemasket River, which will greatly help the APC Management Team implement the projects needed to address years of aquatic habitat degradation and prepare the surrounding communities for future storm events.”

Meeting of the APC Management Team, discussing and prioritizing management actions (credit SRPEDD)

One of the biggest lessons learned throughout this process has been the importance of stakeholder engagement. Belknap explains, “Stakeholder engagement has been a critical part of the APC planning process to fully understand the many complex issues impacting the watershed and the communities that rely on it. We took a thoughtful approach to consider the watershed, and all stakeholder interests, as a whole, and evaluate management actions that address the various needs in a wholistic way.

The H&H study will compliment this wholistic approach by providing insight to the greater picture. As Belknap describes “Assessment like the modeling provided by the Network can help to understand the bigger picture and how impactful individual projects may benefit the system as a whole, which is important when prioritizing actions with limited resources.”

The results of the H&H modeling are currently being used to understand how the various barriers and road crossings along the Nemasket River impact the movement of water downstream. The results will help evaluate how different projects, such as removing a dam or upgrading a bridge crossing, may impact the flow of the river and how quickly the APC may drain after a large rain event. This information will improve the ability to prioritize projects based on which projects will have the greatest impact on improving flow, mitigating flooding, and restoring water quality.

Building off the H&H modeling, the team secured additional funding from the Department of Fish and Game’s (DFG) Division of Ecological Restoration (DER) to further the advancement of hydrologic and hydrological modeling in the Assawompset Ponds Complex and Nemasket River watersheds. This funding from the DER helps complete the next steps identified. As Belknap adds “Horsley Witten will expand the model further downstream, as well as conduct some additional assessments and modeling of groundwater in the watershed. We will also be conducting additional outreach and assessment to further advance high priority implementation projects.”

Barriers, such as the Wareham Street Dam in Middleborough, alter the natural flow of a river system, and can disrupt the journey of river herring and other migratory species (credit SRPEDD)

The hydrologic and hydraulic (H&H) modeling is a part of ongoing climate resiliency work at the Assawompset Pond Complex (APC). In early 2020, the APC Management Team, consisting of members from the six stakeholder communities, were awarded a grant from the MA Division of Ecological Restoration to design a floodwater management program. With assistance from SRPEDD, the Nature Conservancy, Mass Audubon, Manomet, and Horsley Witten, the team reviewed all previous studies of the APC and prioritized actions that would improve floodwater management. As a result of this work, top priority actions were identified, which included conducting H&H modeling, developing a watershed management plan, and serval other projects such as dam and culvert replacements, wetland restoration, and removal of sediment deposition.

To date, the Assawompset Pond Complex (APC) has also secured a Municipal Vulnerability Preparedness (MVP) program grant. With the award, the APC Management team will complete one of the other identified priority projects and finish the Assawompset Pond Complex and Nemasket Watershed Management and Climate Action Plan. The plan is expected to be completed by Summer 2022.

The SNEP Network is a project of the New England Environmental Finance Center and is funded by the U.S. Environmental Protection Agency’s Southeast New England Program. For more information about upcoming SNEP Network webinars and events, other assistance and training opportunities and resources, or to get in touch with us, visit the SNEP Network’s website at snepnetwork.org.