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Watershed Surveys and Planning

Watershed Surveys and Planning

Overview

Watershed planning studies require a letter from a municipality to the NRCS State Conservationist requesting a watershed study, River Basin study or Floodplain Management study. Requests can be made by a municipality, nongovernmental organization, partnership group, or the state. Part of the cost for most studies is paid by the requesting agency or organization.

Section 3 of Public Law 83-566 provides for assisting sponsoring local organizations to develop a plan on watersheds not exceeding 250,000 acres. During planning, problems such as water quality, flooding, water and land management, and sedimentation are evaluated and works of improvement are proposed to alleviate problems. The resulting watershed plans estimate benefits, costs, cost- sharing rates, and arrange for operation and maintenance necessary to justify Federal assistance to install works of improvement.

Section 6 of Public Law 83-566 provides for cooperation with Federal, State, and local agencies in making investigations and surveys of river basins as a basis for the development of coordinated water resource programs. Reports of the investigations and surveys serve as guides for the development of water, land, and related resources in agricultural, rural, and urban areas within upstream watershed settings. They also serve as a basis for coordination with major river systems and other phases of water resource management and Surveys and Planning development.

NRCS Provides Assistance to NJ Water Supply Authority

Lockatong and Wickecheoke Creek Watershed Sediment and Phosphorus Source Report

In 2005 a Memorandum of Agreement was signed, at the request of the New Jersey Water Supply Authority (NJWSA), for the Natural Resources Conservation Service (NRCS) to conduct a study to determine, in part, the sources and amounts of sediment entering the streams and being deposited into the Canal. The study was to focus on the Wickecheoke (17,015 acres) and Lockatong Creek (17,810 acres) Watersheds which represent nearly 65 percent of the total New Jersey influent drainage of 53,860 acres to the D&R Canal.

The identified problem is the continued sedimentation of the D&R Canal which results in annual public and private costs of nearly $3 million. The Canal serves as the water supply conduit to over 1.5 million Central New Jersey residents. It is also the recreational centerpiece of a 63 mile long linear state park.

A combination of Section 319 (of the Clean Water Act) and PL83-566 Watershed Protection and Flood Prevention Act funding was used to fund this study.

Analysis

The two watersheds were subdivided into a total of six HUC-14 subwatersheds. NRCS identified over 1500 crop fields in the Lockatong and Wickecheoke Creek watersheds. A random sample of twenty percent of these 1500 crop fields was taken. The twenty percent sample amounted to 308 fields on which the annual soil losses (soil erosion) was determined using the Revised Universal Soil Loss Equation (RUSLE). RUSLE has factors related to rainfall, soil erodibility, length and percent of slope, cover management and conservation practice. Annual soil loss that exceeds the T value results in the degradation of the soil resource. Only 18 of the 308 fields sampled had this soil loss. Twelve of the 18 fields were located in the Upper Lockatong Creek subwatershed. Crops grown in these fields were primarily soybeans and mixed vegetables. Most of the remainder of the crop fields were in permanent hay resulting in very low soil losses on a per acre basis. A gross projected soil loss of 11,978 tons per year results when the average subwatershed erosion rates are projected for all the cropland.

  This document requires Adobe Acrobat.                      
Lockatong and Wickecheoke Creek Watershed Sediment and Phosphorus Source Report (3.0 mb) - amended December 2007

The forest land use category accounts for about thirty one percent of the area of the Lockatong and Wickecheoke watersheds. These forests are mostly smaller woodlots but a few larger forested patches are present in some large forested wetlands throughout the watersheds and on very steep slopes in the southern reaches of the watersheds. Commercial woodland harvests are very limited in this watershed (Shuart, 2006). Forestry activity in the watershed is normally limited to timber stand improvement, some pre-commercial thinning and small scale timber harvests. Timber harvest activities are also severely limited in wetlands by the NJ Freshwater Wetlands Act and along streams by the Flood Hazard Area Control Act (“Stream Encroachment”). Shuart reports that he knows of no erosion problems in woodlands in the watershed and feels that the limited forest activity should not cause excess sediment sources from woodlands. The NJ State Forest Service does not maintain data on timber harvests.

The 10,763 acres of forestland in the watershed has an estimated erosion rate of 0.1 ton per acre per year which results in 1,076 tons of soil erosion from forestland in the watershed. A sediment delivery ratio of 33 percent yields 355 tons of sediment to the D&R Canal.

Field observations indicate that streambank erosion, which occurs throughout the watershed, is a contributing source of sediment to the Canal. Streambank erosion not only serves as a source of sediment but is also a significant threat to the integrity of several county and municipal roads. Episodic events such as Hurricane Floyd and other intense precipitation events may be putting large loads of sediment and rubble into the streambeds which in turn move downstream incrementally, similar to a conveyor belt, into the Canal. Depending on the methodology used, there is an estimated range of 248 to 12,295 tons of soil loss per year due to streambank erosion.

An analysis, using GIS technology, of the stream drainage density vs. the effective drainage density (includes the road network) shows that the drainage density of the watersheds and their subwatersheds is increased significantly by the road network. Field observations of both paved and unpaved roadways in these watersheds indicate that there can be a disproportionate (in terms of the land area affected) amount of sediment moving from both the road network and/or its drainage system and unprotected (from erosion) outlets.

Also, where road stream crossings occur, on both paved and unpaved roads, there is uncontrolled road runoff entering the stream without any sort of pre-treatment. Frequently there is little, if any, area for the installation of a detention basin, check dams or other structural measures due to the steep slopes and relatively narrow stream corridors. A total of 3723 tons per year of soil loss is estimated to occur from paved and unpaved road surfaces exclusive of any road treatment (such as sand, etc.) used for deicing and winter traction.

Construction sites in the watershed represent a very small portion of the overall land use. There is minimal sediment delivery from construction sites of these sizes due to the relative lack of connection to the existing natural drainage network. Construction activities within this watershed do not have a significant impact on sediment production to the D&R Canal.

Results

Sediment yield (reaching the D&R Canal) is estimated to be coming from the following sources: cropland, forestland, roadways and associated drainage, and stream banks.

NRCS provides assistance in the Millstone River Watershed

NRCS assisted five counties and their respective Soil Conservation Districts survey and assess flood damage and review potential mitigation plans along the Millstone River. Their findings and related figures from the report were presented at a public meeting in Somerset on Wednesday, April 20. They are available for download here.

  These documents require Adobe Acrobat.                      
Millstone River Watershed Flood Damage and Mitigation Report (1.6 mb) (updated to include figures listed below)

Figures that accompany the Millstone River Watershed Report listed here are in jpg format.

Assistance in Repaupo Creek Watershed

April 1996 preliminary report prepared by USDA, Natural Resources Conservation Service in cooperation with the Gloucester County Soil Conservation District presents history and environmental setting of the watershed and offers alternatives for reducing flood damage.

  This document requires Adobe Acrobat.                      
Repaupo Creek Watershed - Preliminary Estimates of Costs and Benefits of Alternative Solutions for Flood Damage Reduction  (621 kb)

 

Watershed Surveys and Planning - Typical Projects

Examples of River Basin studies have been used to identify potential watershed projects include:

  • State Erosion, Sediment and Animal Waste Study (SESAW)
  • South Branch Rockaway Creek (basis for state regulations to store 1 year storm volume)
  • Still Run (look at alternative regional sites for stormwater management)
  • State Agricultural Water Needs Study - done in cooperation with the State Soil Conservation Committee, US Geological Survey and other agencies and organizations
  • Musconetcong/Pohatcong Preauthorization Planning Report
  • Crosswicks Creek Preauthorization Planning Report
  • Flood Plain Mgt Studies - work with FEMA or to evaluate alternative control measures for state/county/town

Past technical studies and surveys have included:

  • Hydrology/hydraulic evaluations with town management options to reduce flood damages,
  • Individual building flood assessments and individual flood warning response plans for homeowners and business owners (sponsored by municipality),
  • Collaboration with towns and natural resource Geographic Information System (GIS) data analysis to assist with community planning,
  • Erosion and sedimentation reduction plans that will improve water quality,
  • Technical inputs to watershed partnership initiatives resulting in locally implemented watershed action plans, and
  • Dam breach analyses and emergency operation plans for NRCS watershed program dams.

Program Contact: David Lamm, State Conservation Engineer, 732-537-6071