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St. Croix East End Watershed Restoration Project

Introduction

In September 2011, through the Conservation Technical Assistance Program (CTAP), NRCS awarded a grant to the St. Croix Environmental Association (SEA) to complete engineering designs and plans for two priority restoration projects identified in the St. Croix East End Marine Park (STXEEMP) watershed management plan.

CTAP provides conservation technical assistance to landowners and nonprofits to apply best management practices on private land to conserve and improve natural resources. CTAP assistance includes habitat protection, restoration, development or enhancement for upland wildlife, wetland wildlife, threatened and endangered species, fisheries, and other types of wildlife.

BackgroundEndangered Acropora corals.

Coral reef ecosystems in the USVI and Wider Caribbean Area are threatened by many natural and man-made stressors, but the primary threat to our coral reefs is sediment.  Most developments lack properly designed and installed storm water drainage systems, and many are accessed by unpaved road networks.  These unpaved road systems are both sediment sources and sediment delivery systems, routing sediment-laden runoff directly to sensitive coastal areas.

Sediment (and bacteria) impairs water quality in many bays in the St. Croix East End Marine Park (STXEEMP).  These pollutants harm the ecological health, recreational use, and commercial resources of the STXEEMP. As a result, coastal managers identified the St. Croix East End watersheds as priority areas for pollution prevention and restoration work.

Project Sites

Southgate WatershedSevere erosion in gut on Adams family pasture land, St. Croix.

The Southgate Watershed is a mixed use watershed that contains Southgate Pond, one of the largest salt ponds in the USVI and an ecologically-significant habitat. Development in the watershed has increased paved surface area, altered water flow patterns, and decreased groundwater recharge. These dramatic increases in storm water runoff have caused severe erosion of gut (intermittent stream) banks in the watershed.

One priority area – a severely eroded gut section on pastureland in the watershed – was selected for restoration. The eroded section of the gut is now10-15 feet deep and ~1,500 feet long, and the property owners report that the erosion has moved steadily upstream at ~10-15 feet per year. Sediment from the eroded gut can be seen downstream; and sediment-laden water from the gut discharges into Chenay Bay, listed as impaired for turbidity by DPNR in 2010.

  • Objective: Design complete engineering plans & drawings to stabilize the eroding gut.
  • Goals:
    • Protect mangrove wetlands and salt pond habitats for wildlife [protected Bahama ducks (Anas bahamensis), piping plovers (Charadrius melodus), brown pelicans (Pelecanus occidentalis), pied-billed grebes (Podilymbus podiceps), and Caribbean coots (Fulica caribaea)];
    • Reduce sediment loads to Chenay Bay and STXEEMP; and
    • Protect coral reef habitat for endangered elkhorn and staghorn corals (Acropora sp.), juvenile spiny lobster (panulirus argus), and nesting habitat for threatened and endangered hawksbill and green sea turtles (Eretmochelys imbricate and Chelonia mydas).
Solitude WatershedRoad erosion in Hope and Carton Hill leading to sedimentation of Solitude Bay.

The Hope and Carton Hill/ Yellow Cliffs residential area lies in the upper reaches of the Solitude watershed. These neighborhoods have almost 5 miles of very steep, mountainous, and unpaved roads. The roads have many deep ruts and gullies that erode and carry storm water and large amounts of sediment during rain storms. All of this runoff and sediment ultimately wash into the main gut of the watershed; carrying an estimated 112 tons of sediment per year – 11 times higher than under natural conditions – into the marine habitats of Solitude Bay and the STXEEMP.

  • Objective: Develop a Road Drainage Master Plan to reduce erosion of the steep, dirt road network serving the Hope and Carton Hill neighborhood.
  • Goals:
    • Reduce sediment loads to Solitude Bay and STXEEMP;
    • Protect nesting areas for threatened and endangered hawksbill and green sea turtles (Eretmochelys imbricata and Chelonia mydas); and
    • Protect coral reef habitat for endangered elkhorn and staghorn corals (Acropora species) and juvenile spiny lobster (panulirus argus).

Project Accomplishments

Southgate WatershedPartners visit eroded gully on Adams family pastureland, St. Croix.

SEA contractor, Horsley Witten Group, Inc., completed engineering drawings and designs to stabilize the most severely eroded section of the Adams Family gut in September 2012. HW confirmed the rate of head-cut migration to be approximately 10-15 feet per year, through the use of aerial photography. Their design is limited to the emergency repair of the headcut to prevent additional erosion.

The restoration design utilizes a combination of “soft” and “hard” stabilization techniques. “Soft” stabilization measures include natural materials like coconut (coir) fiber mats, grasses, and various shrubs and trees. “Hard” stabilization practices proposed include riprap and large boulders (i.e., quarry stones). Other design alternatives considered were concrete stabilization, grouted riprap, and gabions.
Project partners and landowners are currently seeking additional funding to implement the stabilization designs.

Solitude Watershed

Hope & Carton Hill HOA Meeting to discuss draft Road management plan.SEA contractor, Horsley Witten Group, Inc. (HW), also completed a Master Drainage Plan for the Hope and Carton road network in January 2013, and designed and installed a demonstration rain garden in the neighborhood.

In October 2012, the project partners, together with Hope & Carton Hill residents, installed the first demonstration rain garden in the watershed. SEA, HW and NRCS staff worked with homeowners, contractors, and volunteers to excavate and shape the rain garden, donate & deliver mulch and compost, and plant over 50 native or naturalized species purchased locally or donated by partners and residents. The rain garden got its first test a few weeks later, handling ~2 inches of rainfall.

HW & NRCS staff also held several meetings with over 16 neighborhood residents to gather information about problem areas in the watershed, solicit input to the Road Management Plan, and present the draft Drainage Plan and gather input and recommendations to improve the plan.

DocumentsHope & Carton Hill rain garden 7 months after installation.

For More Information

Please contact the St. Croix Field Office at 340-692-9632 x3.