The Elbow Coulee floodplain and project site lie on the left bank (north side) of the Twisp River in an area where flows generally run in an easterly direction.  The floodplain is approximately 800 feet at its widest point and contains a complex of perennial beaver ponds and three historic side channels.  In the last 60 years, debris clearing and dike construction in the main channel have concentrated river flows and increased stream power.  This has led to degradation of the riverbed, loss of smaller sized bed material, and disconnection from the adjacent floodplain and historic side channels.  Over time, the river abandoned the flood plain and side channels, resulting in the loss of critical spawning habitat, high-flow refugia, and rearing habitat for listed fish.

In the decades following the historic 1948 flood, people began clearing the Twisp River to remove large woody debris.  Many areas in the mainstem channel, including the area adjacent to the Elbow Coulee flood plain, currently have extremely high velocities and homogenous habitat types that are not favorable to the key life stages of the anadromous salmon, specifically during the spawning and rearing life stages.

There are three historic side channels in the Elbow Coulee floodplain.  The first, an active side channel on the river right bank, starts above the project area and is about 750 feet long.  This channel provides some winter refugia and rearing habitat for fish in the project area.

On the river left bank, a well-defined historic side channel, called the primary side channel, starts near RM 6.65 and extends through the floodplain for about 1,000 feet before exiting back to the river near RM 6.44.  Photographs of the 1948 flood show the mainstem Twisp River flowing through the primary side channel.  A manmade rock and earthen dike, built sometime after 1948, extends along the left bank from about RM 6.65 to RM 6.62, preventing live flows from entering the abandoned flood plain and primary side channel.  The levee is four feet tall and extends approximately 300 feet.  With the levee and subsequent river incision, the primary side channel entrance is approximately six feet higher than the main river channel.  The primary side channel outlet has stable banks with coarse substrates and is accessible to fish.

A smaller side channel, referred to as the secondary side channel, starts on the river left bank near RM 6.63.  The secondary side channel lies south of the primary side channel and extends about 450 feet through the floodplain before returning to the river near RM 6.49. The smaller secondary side channel lacks the definition of the primary side channel, but can function as an existing floodplain feature.  The outlet is steep, contains large substrate materials, and is inaccessible to fish.

Project elements will reconnect the river with the abandoned flood plain and restore fish habitat.  
• Construct a rock sill in the river left bank at the entrance to the primary side channel inlet that will be a grade-control structure for flows exceeding elevation 1942;  
• Install a woody debris structure at the upper end of the primary side channel for erosion protection.

Staging and Access
The initial staging area will be located on the south side of the Twisp River Road just before the first crossing as shown on Figure 1 attached. An excavator will cross the Twisp River using the area adjacent to the initial staging site and traverse along the right river bank of the river until reaching the secondary channel outlet area at which point the excavator will cross the river again to the left river bank. It will continue to traverse the left riverbank of the Elbow Coulee floodplain until it reaches the reconnected channel entrance location.  The excavator will cross the river four times: twice to reach the project site, and twice to return to the staging area.  The area of impact for the staging and access route is approximately 0.5 acre.

Excavation and Disposal
Rock Sill
Excavation of the sill area is approximately 70 cubic yards of earthen material to get to the sill elevation of 1942 feet. The rock sill will be a trapezoidal shape with a low flow notch.  Rock that is 2.5  to 3.5 feet in diameter and round, angular, and subround, will be used to construct the sill entrance to the new channel; this rock will be obtained from the site.  Roughly 120 cubic yards of additional earthen material will need to be overexcavated and replaced with rock.  This results in approximately 75 (blocky, preferred) to 140 cubic yards (round) of 3.5-foot diameter rock.  Excavated material will be disposed of on site.  Wood taken out will be salvaged for use in the woody debris complex (see below).

Woody Debris Materials
One field-designed woody debris complex will be installed at the upper end of the primary side channel, just downstream of the rock sill.  The wood material will be found on site.

Construction Work Period and Dewatering
The construction work period will be from July to August. In-water work period will be from mid-July to mid-August. All in-stream work is expected to be conducted in the wet so no dewatering will be necessary. However, there exists the potential for severe storm event(s), which could cause the channel areas to become inundated, and require isolation of the work area to prevent entrainment or injury to fish.  Therefore, a dewatering contingency is itemized in the budget.

Rock approved for retrieval from the main channel will be obtained during this time.

Vegetation
All areas impacted by construction including the access route (approx. ½ acre) will be revegetated according to USFS regulations and the requirements of all federal and state permits as well as the USFWS and NMFS biological opinions resulting from consultation.