DesignReport10_30_17rev.pdf

Fish Creek Crossing Stream Simulation Design Report

October 30, 2017

Fish Creek Crossing culvert looking at the inlet, May, 2017

Jim Wilcox Plumas Corporation P.O. Box 3880 Quincy, Ca. 95971

Project Description:

The Sequoia NF (FS) is intending to replace the existing arch culvert on Forest Road 22S05 at the Fish Creek crossing with a bridge. The crossing was originally built over the confluence of Fish Creek and Jackass Creek. Since installation the culvert has destabilized the two channels, leaving Jackass Creek incised and Fish Creek perched with headcuts moving upstream. The project would provide a channel/floodplain design through the bridge footprint to stabilize the upstream channels, reduce the sedimentation downstream, and optimize the movement of native fish species through the crossing. This is of particular value given the concurrent development of five (5) meadow restoration projects totaling 210 acres in the watershed upstream of the crossing. These meadow projects, Powell, Granite Knob, Little Troy, Troy and Jackass meadows, are intended to re-establish the hydrologic connectivity of the channels and floodplains. Collectively, these activities would improve water quality, timing of flows along with enhanced aquatic and terrestrial habitats available to the South Fork Kern River system.

Conceptual Design Narrative:

Plumas Corporation (PC) conducted cross-section and longitudinal profile surveys in mid-May, 2017.

After data collation and analysis, a draft conceptual design was developed and staked (flagged) on the ground in mid-June, 2017. Control elevations were established and ultimately rectified with FS bridge elevations. Early review of the design was complicated by the initial differences in PC and FS datum elevations. A common point was established in June at centerline culvert/centerline road to serve as the common datum of 7406.28. All PC design elevations have been rectified to this datum.

The replacement of a culvert with a 50-foot span bridge will improve floodplain function significantly.

However, the full width of the historic floodplain will not be restored. This will result in higher than ‘natural’ shear stresses on the channel/floodplain feature and materials through the bridge footprint, as well as some distance upstream and downstream of the bridge. Therefore this reach of constructed channel/floodplain would be designed to act as a hardened, anchor section with energy dissipation, energy resistance and grade control functions. The constructed reach would not have the geomorphic response characteristics of the up- and downstream reaches. Fill material would be comprised of 2-foot minus rock with at least 20% soil to provide plant medium and seal structure against leakage. Total fill would be approximately 600 yds3. Some material may be available onsite, with the bulk of the rock material imported.

There is some debate over the efficacy of anchoring the residual alluvial wedge of Fish Creek, while concurrently raising the base level of Jackass Creek. Sierra Nevada watersheds, north to south, have suffered significant degradation from channel incision processes related to land use. This is due to the fact that the Holocene alluvium is predominately fine-grained, with coarser, more resistant material associated with the Altithermal period at some depth. With severe channel incision already present in the upstream Troy Meadow area, instituting extra precautions against further incision migrating upstream is thought prudent.

Since the stability of the design channel(s) is not dependent on a particular discharge, the channel dimensions are developed to provide the most effective aquatic organism passage conditions for the range of flows where movement typically occurs. The principal parameters are width-to-depth ratio and riffle/pool frequency. The width-to-depth ratio is intended to maintain adequate depth for movement at lower discharges while not promoting excessive velocities at higher flows. The bed profile is designed to provide 60% riffle and 40% pool. Each riffle/pool segment totals a length of ~60 feet. This allows for frequent resting areas between short, steeper riffles. Dimensions summarized: channels- 12’ width, 0.75’ mean depth; channel thalweg depth 7393.20 or less at bridge entrance, floodplain elevation 7394.20 or less at bridge entrance. The appended photo series illustrates the evolution of a similar structure over a 4-year period

Figure 1. Design plan view

Channel Velocities @ "Bankfull" Slope/Area Method ‐ Riffle only

Mannings Formula: V = 1.4/n(r)^2/3(s)^1/2 Chan Area: 9 sqft Ave. Width: 12 ft

Q = AV

Wetted Perimeter: 13.5 ft Ave. Depth: 0.75 ft

Hydraulic radius = A/WtP

Slope: 0.04 ft/ft *Enter slope as a decimal. Ex: 0.0055

Roughness Co.: 0.035 Hydraulic Radius: 0.666667

1.4 40 0.763143 0.2

V = 6.1 fps

Q = 55 cfs

Slope/Area Method ‐ Pool only

Mannings Formula: V = 1.4/n(r)^2/3(s)^1/2 Chan Area: 22.5 sqft Ave. Width: 15 ft

Q = AV

Wetted Perimeter: 18 ft Ave. Depth: 1.5 ft

Hydraulic radius = A/WtP

Slope: 0.005 ft/ft *Enter slope as a decimal. Ex: 0.0055

Roughness Co.: 0.045 Hydraulic Radius: 1.25

1.4 31.11111 1.160397 0.070711

V = 2.6 fps

Q = 57 cfs

Enter values in shaded cells

Enter values in shaded cells

Figure 2. Proposed cross-section at Station 00+00, 90 feet upstream of the culvert inlet

7390.00

7392.00

7394.00

7396.00

7398.00

7400.00

7402.00

7404.00

7406.00

7408.00

7410.00

0 50 100 150 200 250 300 350 400

El e va ti o n fe e t)

Distance (feet)

Fish Creek Crossing‐ Cross‐section #3 (proposed) @ sta. 00.00 ‐ 90 feet upstream of bridge entranceLB RB

20 X vertical exaggeration

Figure 3. Proposed cross-section at Station 0+90, @ bridge inlet

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7398.00

7400.00

7402.00

7404.00

7406.00

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7410.00

‐25 ‐15 ‐5 5 15 25 35 45 55 65 75

El e va ti o n fe e t)

Distance (feet)

Fish Creek Crossing‐ Cross‐section #3a (proposed) Sta. 0+90 at entrance to bridge

LB RB

Q100 El. 7402.00

Thalweg elevations‐ 7393.20

Jackass Creek

Fish Creek

Floodplain elevation 7394.20 Finish grade

Figure 4. Proposed cross-section at Station 1+18, @ bridge exit

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7398.00

7400.00

7402.00

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7408.00

7410.00

‐25 ‐15 ‐5 5 15 25 35 45 55 65 75

El e va ti o n fe e t)

Distance (feet)

Fish Creek Crossing‐ Cross‐section #3b (proposed) Sta. 1+18 at exit from from bridgeLB RB

Q100 El. 7401.50

Thalweg elevations‐

Jackass Creek

Fish Creek

Floodplain elevation 7393.30

Finish grade

Figure5. Fish Creek Crossing Design Profile

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0 50 100 150 200 250 300

El e va ti o n fe e t)

Distance (feet)

Fish Creek Design Channel Profile

Cross‐section

Cross‐section 3b

Photo 1: Yellow Creek in Humbug Valley one month after construction (11/22/2013)

Photo 2: Yellow Creek in Humbug Valley (6/6/2014)

Photo 3: Yellow Creek in Humbug Valley (7/16/2015)

Photo 4: Yellow Creek in Humbug Valley (5/24/2016)

Photo 5: Yellow Creek in Humbug Valley (6/9/2017)