As the Mill River watershed is an interconnected system, the LWTB project recognizes that both upstream and coastal interventions were required to address two of the largest vulnerabilities faced by surrounding communities during Superstorm Sandy: coastal surge and stormwater flooding. The interventions proposed within HLSP not only address stormwater flooding concerns, but also look to increase capacity and efficiency of the northern end of the system, while simultaneously introducing recreational and educational opportunities for citizens to learn about and connect with their natural environment.
Interventions within HLSP are organized into four sections:
- Dams, Gatehouse and Bridges
- Northwest (NW) and Northeast (NE) Ponds
- Environmental Education and Resiliency Center
- Greenways, Gateways and Waterfront Access.
As a stakeholder and a subrecipient of disaster recovery funds from GOSR, the NYS Office of Parks, Recreation and Historic Preservation (State Parks) is responsible for funding the long-term operation and maintenance of the overall HLSP improvements.
FIGURE 11: HLSP PROPOSED INTERVENTIONS
Dams, Gatehouse and Bridges
This section focuses on improvements to the Mill River dams located within HLSP and enhances the function of the dams as a key instrument for flood mitigation. This work also includes design of pedestrian bridges that are part of the adjacent shared-use path system that increase access and connectivity throughout the park.
The NW Pond and dam were constructed in the 1960’s around the same time as a large (96” diameter) drainage pipeline was installed through Hempstead to discharge stormwater runoff from the surrounding community into the NW Pond. The dam provided attenuation of peak stormwater flows from the 96” pipe, allowed sediments to settle out of the runoff, and also prevented floatables from reaching downstream into Hempstead Lake. As a result of the dam being breached in 2012, flow through the NW Pond is uncontrolled bringing sediment and floatables into Hempstead Lake.
Modeling has indicated that constructing a new dam, with an appropriate spillway elevation, at the NW Pond will lessen the impacts to the larger Hempstead Lake Dam during a major storm event. A new NW Pond dam will maintain more water within the pond limits, encouraging the growth of wetlands which in turn will provide filtering and enhanced water quality. The dam will help attenuate peak flows from the upstream drainage collection systems allowing for better control of flows in the overall watershed, and flood mitigation. By reestablishing the depth in the pond area, the dam will allow sediment to be filtered out before reaching the downstream waters (especially after the “first flush”), thus enhancing and improving water quality downstream.
Once the NW Pond Dam is in place, flows can be directed downstream of the dam through an open channel and culvert under the Southern State Parkway and into Hempstead Lake. A timber pedestrian bridge will be provided to carry a shared use path that encircles Hempstead Lake over this channel. Installation of the bridge will allow removal of existing twin 60” diameter pipes that currently limit flow through the channel (and also create the potential for an unplanned impoundment if blocked), while providing for uninterrupted access to the pedestrian pathway. Modeling has indicated that the removal of the twin pipes would enhance the flow between the NW Pond and Hempstead Lake, which is an important aspect of the project goals. The bridges will be designed to accommodate emergency vehicles, thereby improving emergency access and response times, maintenance vehicles, pedestrians, and horses.
The Hempstead Lake Dam, gatehouse and pipe arch were constructed in 1873. The dam’s outlet-controls (currently not functional) are housed in the historic gatehouse structure, that directs water flows through an attached brick pipe arch that extends from the dam into South Pond. HLSP will replace all five of the sluice gates at the dam and provide new gate controls in the gatehouse. An operating plan will be developed to actively manage water flow in small and large storms events. In all, installation of new outlet gates, inspection catwalk and water level monitoring equipment at the dam gatehouse will allow for control of flows through the Park, over the dam, and into the lower reaches of the watershed. Flow-control is key to flood protection and dam safety, as well as maintenance of lake levels for recreational and ecological purposes. In particular, the ability to draw down lake levels prior to the onset of an extreme precipitation event, may reduce peak flows downstream, and will enhance dam safety. As a part of this project, and in accordance with NYSDEC dam safety requirements, trees and vegetation will be removed from the dam to ensure the dams integrity and to allow for proper, ongoing inspections. In addition, vandalized stonework at the historic inlet gatehouse at South Pond will be restored to ensure the integrity of the structure and historical accuracy.
The Dam work proposed throughout HLSP is being progressed in accordance with the overall LWTB project to help improve flood management, water quality, dam safety and ecological conditions throughout the Mill River watershed. This project will enhance public safety and resiliency, provide connections to the adjacent communities, encourage usage of the natural facilities in the Park, and provide environmental education and interpretation opportunities. These can be seen in Figure 11.
Northwest and Northeast Ponds
The NW and NE Ponds, known as the “North Ponds,” are located in the northern portion of HLSP and are fed by the Mill River, groundwater, and from multiple stormwater drainage systems. The ponds are separated from Hempstead Lake by the Southern State Parkway. Improvements to the NW and NE Ponds (in addition to the dam replacement described above) include dredging to increase storage capacity, wetland creation and restoration, and installation of a culvert and floatables catcher. Currently, the North Ponds area is extremely underutilized, owing to degraded environmental conditions, extreme litter accumulation, and dying wetlands.
Over time the watershed for the ponds has become urbanized, increasing run-off volume and pollutant load. Flow into the ponds carries pollutants from urban run-off. There are significant floatables deposits, sediment loads and oil residue apparent near many of the outfalls. Water sampling confirms this pollutant load, particularly during the first flush at the onset of a rain event. The high run-off sediment load has filled the creek channel and the high velocity of the runoff entering the Mill River channel has resulted in significant erosion of the channel that is deposited into the ponds and surrounding area. This project seeks to mitigate the pollutant levels that enter the ponds and utilize new and restored wetlands to filter other pollutants from the runoff, which in turn will improve the water quality entering Hempstead Lake and downstream into the bay. By installing a floatables catcher at the Northeast corner of the Northeast pond, floatable deposits within the Ponds and downstream Hempstead Lake will be significantly reduced. The improved wetlands will also provide enhanced passive recreational opportunities, including bird watching, as native plantings are expected to restore populations of local and migratory bird species.
Overall, the NW and NE Ponds environmental and stormwater mitigation improvements will result in improving stormwater management, improved water quality, reduced erosion through stabilization of the channel within the Park, creation and restoration of diverse habitats and ecosystems and enhanced social connectivity with a continuous greenway extending to the surrounding neighborhoods.
Environmental Education and Resiliency Center
The Environmental Education and Resiliency Center (The Center) at HLSP will be a new and unique hands-on learning center about storm resiliency and environmental management, and will provide educational opportunities and an emergency coordination center for the immediate communities to aid with disaster response. The facility will provide an outreach and educational opportunity for the local community, as well as nearby user groups and school districts that frequent the park.
The Center is being designed to act as a “coordination center” during times of emergency for the following purposes:
- “Command Post” for local disaster response coordination either for agency staff or other agencies such as the NYS Park Police and the Nassau County Police Department. The existing parking area (Field 1) is also utilized by Public Service Electric and Gas (PSE&G) for emergency response staging of equipment in advance of severe weather events. The Center will provide a location for PSE&G staff to coordinate equipment staging, enhancing their emergency response to restore critical utilities and thereby help to promote safety and economic resiliency in the community and region.
- The Center may also serve as an information center if needed, for local residents after an emergency. Parking is available at Field 2 or access via the greenway that provides connection points to the surrounding neighborhoods and communities, some which are predominately low to moderate income. The building will include an emergency generator to provide resiliency and continued functionality during power outages.
- Monitoring station for water levels in HLSP ponds and lakes to inform water management decisions during storm events.
The Center is also being designed to include space to provide for additional partnerships with environmental education, non-profit organizations, educational institutions, community organizations, such as the Nassau County Law Enforcement Explorer Program (Explorer Program), that will use the Center for training space to promote and deliver their programs within the park. The Explorer Program is a volunteer program that provides an opportunity for at risk and low to moderate income young adults to receive basic law enforcement training and to learn about career opportunities within law enforcement. In addition to training and education, volunteers participate in community service events throughout the year to encourage volunteerism and build stronger communities. The space provided to the Explorer Program will serve as a center for local community outreach by the police, educating and positively engaging young people through mentoring and education; further strengthening the connection to the community, giving youth an opportunity for a sense of place and ownership to the park and surrounding community.
Additionally, the Center will also serve a central focal point and core for the park with connections to the greenway, providing educational and community spaces connected to an overlook deck with views of Hempstead Lake and a location where park information can be distributed explaining climate change impacts, community resiliency processes, environmental preservation, and other items of local relevance. The Center will also provide essential facilities to help with building partnerships with local school districts to utilize the education space and wet lab for hands-on learning and activities; engaging young minds through activities that reflect the local surroundings and foster stewardship. The Center will be focused primarily around the importance of environmental education and stewardship, providing a connection between the community and the environment, while also providing a resource, specifically during extreme weather conditions. There will also be information about the Mill River system’s local wildlife and the history of the area.
The Center will be constructed to reduce environmental impacts through an approach that focuses on lower operating costs through environmentally conscious building design. The building will be used to educate users about sustainable building practices and construction. The building will be designed with the following key features:
- Robust and sustainable exterior envelope optimized to suit local climate demands.
- Awareness of solar impacts (i.e. siting) and control (i.e. glazing) to reduce heating and cooling loads.
- LED lighting with occupancy sensing and daylight harvesting to reduce electrical usage.
- Photovoltaic roof panels to offset electricity energy usage.
- High-efficiency, low/no water plumbing fixtures.
Greenway, Gateways and Waterfront Access
Access improvements, including greenways, gateways and new waterfront infrastructure, will increase the community’s connection to Mill River, an important component of the winning RBD LWTB project concept. Connections to surrounding communities and in particular, Hempstead High School students, and other surrounding neighborhoods will draw visitors to the lake and river, with the enhanced, direct, and ADA compliant access this project provides to the water.
Greenways and trails will provide a physical connection linking the ecological network and the communities along the Mill River project area. The greenway provides a unique opportunity to connect the public and provide them with the opportunity to walk the river and learn along the way about the river system through educational signage.
On a daily basis, the trails and greenway will be open to the public for recreational use (walking, jogging, biking, horseback riding, bird watching, etc.) providing connection points to the surrounding neighborhoods and an economical way for people to exercise, increasing the health and well-being of its users, with attention to developing physical environmental connections to nearby underserved communities. The trails and greenway will also provide access to the ponds and lake for other types of recreation such as fishing and kayaking.
Improvements to an existing parking area, utilizing green infrastructure, will be implemented to provide local and regional patrons with improved access to the park to enjoy the Mill River project area. In addition, this centralized parking lot is in close proximity to local mass transit.
The improvement and creation of gateways into the park will provide new direct, pedestrian access from the adjoining neighborhoods, a significant portion of which are low to moderate income communities. These gateways will also provide a sense of security within the park, by opening views and providing additional access points for emergency vehicles.
The park waterfront enhancements and improvements will include new amenities such as trails along the waterfront; a new crossing at Schodack Brook Bridge to allow users to traverse the entire park from north to south; potential piers/kayak launch area, ADA compliant docks for fishing; educational piers; birdwatching; and open views to enjoy the scenic waterfront.