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Watersheds

A watershed is the area of land where all of the water that is under it or drains off of it goes into the same place. John Wesley Powell, scientist geographer, put it best when he said that a watershed is:

"that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community."

Watersheds come in all shapes and sizes. They cross county, state, and national boundaries. In the continental US, there are 2,110 watersheds; including Hawaii Alaska, and Puerto Rico, there are 2,267 watersheds.

2014 Watershed Rehabilitation Update
The 2014 Farm Bill made about $262 million available for rehabilitation of 151 dams in 26 states, including Wyoming. These watershed management projects provide an estimated $2.2 billion in annual benefits in reduced flooding and erosion damages, recreation, water supplies and wildlife habitat for roughly 47 million people. Projects were identified based on recent rehabilitation investments and the risks to life and property if a dam failure occurred.

Projects in Wyoming include:

  • North Fork Powder River (Dull Knife)
    Abstract
    Dull Knife Dam was constructed in 1965 under the authority of the Watershed and Flood Prevention Act, Public Law 83-566. It was originally designed as a significant hazard dam with an existing rock spillway that was to function as both the principal and auxiliary spillway.  After continued flows through the spillway and subsequent freeze-thaw cycles, noticeable signs of erosion of the fractured rock material had taken place. In 1967, a principal spillway in the form of a lateral concrete weir structure and an associated concrete box conduit was designed and installed to alleviate flow through the rock spillway.  However, occasional ice build-up at the entrance to the conduit still caused water to flow over the rock spillway and continue the erosion process. The condition and continued erosion of the auxiliary rock spillway has caused concern regarding the safety of the structure. As a result, a breach analysis was completed and the dam has been reclassified as a High Hazard Dam.

    Rehabilitation of the dam would require modifications to the structure that include but may not be limited to:
    - Widening the auxiliary spillway.
    - Armoring the auxiliary spillway with an effective energy dissipating structure and associated appurtenances.
    - Raising the top of the dam to pass the design storm through the auxiliary spillway without overtopping the dam.
    - Riprap protection of the existing dike that is located adjacent to the spillway.
    - Lining the interior of the existing 36” concrete drawdown pipe and replacing associated appurtenances.
    - Installation of abutment drains.

    Sponsoring Local Organization
    The Sponsoring Local Organization is the North Fork Water Users Association, a Wyoming non-profit corporation (“Association”). The Association was formed in 1965 to build, maintain and operate an irrigation water storage facility referred to as the Dull Knife Dam (“Dam”), located in Johnson County, on the main stem of the North Fork of the Powder River in the Big Horn Mountains, Section 21, 22 and 27, Township 47 North, Range 85 West. The Association owns the Dam and adjudicated Wyoming Water Rights.  The water stored in the Dam has been used since 1965 for irrigation of several thousand acres of land owned by shareholders of the Association.

    Purpose of the Project
    The existing structure was originally designed and constructed as a Class B Hazard Dam.  The existing auxiliary rock spillway has been continually eroding since the structure was built and has progressively gotten worse over the last 10 years.  This erosion not only occurs when water flows over the spillway but it also progresses from freeze-thaw cycles that continually erode the fractured rock material. A breach analysis was conducted in December of 2004 to see if the Hazard Classification has changed.  The report concludes that damages to homes, ranches, and highways would potentially cause loss of life in the event of a breach.  A breach of the dam would inundate 58 miles of floodplains along the North Fork of the Powder River. Consequently, the hazard classification has changed and the dam has become a High Hazard dam.  Modifications are necessary to assure the structure has the ability to safely pass the design flow requirements for a High Hazard Dam in a safe, stable manner without jeopardizing the integrity of the dam, and that will minimize the risk of property damage, damage to the environment, and loss of human life.

    Proposed Action
    Rehabilitate Dull Knife Dam for the SLO to meet current safety and performance standards for a high hazard dam. The purpose of this Federal action is to continue to provide a supplemental irrigation water supply along with flood control and recreation benefits in a manner that minimizes the risk of loss of human life and is both cost efficient and environmentally acceptable. Dull Knife Dam currently does not meet NRCS safety and performance criteria for a High Hazard Class dam.  Modifications are necessary to upgrade the structure to meet current safety and performance standards.