Hydrology Report

Conner Creek Fish Passage Improvement Project

USDAForest Service Region 5

Shasta-Trinity National Forest

Trinity River Management Unit (TRMU)

Prepared by: /s/ Mark S. Lancaster

CA Registered Professional Forester

Five Counties Salmonid Conservation Program

Northwestern California Resource Conservation and Development Council

Reviewed by: /s/Fred S. Levitan

West Zone Hydrologist

Shasta-Trinity National Forest

June 15, 201

Conner Creek Fish Passage Improvement Project - Hydrology Report – June 15, 2011

I. Description of Proposed Project

The Five Counties Salmonid Conservation Program (5C)[1] in cooperation and partnership with the Trinity County Department of Transportation (DOT) proposes to replace the existing culverts on Conner Creek at Red Hill Road (County Road 415) and Conner Creek Road (County Road 449). Red Hill Road is the sole access and egress route for the Cooper’s Bar Estate subdivision and[CJordan1] Red Hill Lake neighborhoods, providing access to more than 100 private parcels and/or homes. It also accesses Forest Service Road 33N41 and the Hocker Meadow area, the main route to the upper elevations of the Conner Creek watershed. Conner Creek Road is a dead end road that serves approximately 10 private parcels and homes.

The project is located in Section 2 T 33N, R 11W MDBM. Crossing #1 is at milepost 0.06 on Conner Creek Road and Crossing #2 is at milepost 2.4 on Red Hill Road (Figures 1-3). The project is located in the Conner Creek-Trinity River 7th-field subwatershed and Conner Creek is a fourth[CJordan2]-order perennial tributary to the Trinity River (Table 1).

Table 1. Conner Creek Fish Passage Improvement Project watershed hierarchy

HUC4 (Subbasin)Level / 18010211Code / Trinity River
HUC5 (Watershed) / 1801021109 / Canyon Creek
HUC6 (Subwatershed) / 180102110803 / Lower Canyon Creek
HUC7 (Drainage) / 18010211080306 / Conner Creek-Trinity River

Both stream crossings create backwater conditions during moderately high flows (~Q15); the roads overtop during larger flows (Q18 and Q43) and prevent upstream migration for salmonids and resident trout during nearly all flows. The proposed project will replace the existing culverts with structures designed to allow fish to migrate upstream, convey the Q100-year storm flows and allow improved downstream transport of bedload, wood and debris. While the project was recognized as a priority following the Trinity County Migration Barrier Inventory (conducted between May 2001 and June 2002) of stream crossings on county roads (Taylor, 2002), the need for the project increased following the 2008 Eagle Fire which burned the upper 41% of the Conner Creek watershed within the Eagle Inventoried Roadless Area.

The project is proposed because the existing crossings are inadequate to meet federal, state and local goals, policies and objectives for threatened and endangered species conservation and recovery. The crossings fail to meet water quality objectives (refer to Section IV). Specifically, the current stream crossings are deficient because:

  • They prevent nearly all upstream migration of adult and juvenile salmonid fish species and the outlet jumps at both crossings exceed 1+ feet, limiting juvenile salmonid passage during all flows (Taylor 2002; refer to Figure 3);
  • The existing offset baffles that line half of the concrete box culvert floor on Conner[CJordan3] Creek Road jam with debris and are ineffective at improving adult migration following larger storm flows (Figure 3);
  • Both stream crossings impede natural bedload, wood and debris transport;
  • Both stream crossings have the potential to overtop and fail, cutting off access to over 100 private parcels and access to public lands;
  • Both stream crossings, if they were to fail, could yield 750-2,189 cubic yards (yd3) of sediment to Conner Creek (5C DIRT Inventory, 2001; DOT 2011).
  • The 2008 Eagle Fire in the upper portions of the Conner Creek watershed increased the potential peak discharge of small to moderately large storms for the short and mid-term periods. Additionally, the fire increased the potential for sediment, bedload and debris transport (USFS, 2008).

Figure 1. Project Location Map[CJordan4]
Figure 2. Crossing (#1 and #2) Locations[CJordan5]

Figure 3 (photos above). Red Hill Road perched outlet and jump (left); Conner Creek Road crossing offset baffle debris jam (center) and Conner Creek Road outlet jump (right).

Figure 4 (photos below). Multi-plate arch set on concrete abutments on a nearby comparative watershed (Soldier Creek at Evans Bar Road). The left photo is similar to the proposed structure to be installed on Red Hill Road, while a bridge similar to one installed on Little Browns Creek at Roundy Road (right) would be installed on Conner Creek Road.

Conner Creek is designated as critical habitat for threatened coho salmon by NOAA’s National Marine Fisheries Service (NMFS) and as a tributary to the Trinity River, it is designated as impaired by excess sediment and siltation and excess water temperature under Section 303(d) of the Clean Water Act by the State Water Resources Control Board. There is an EPA-approved sediment Total Maximum Daily Load (TMDL) in place for the Mainstem Trinity River system (EPA, 1999). The five-acre project area and stream crossings are located within designated Riparian Reserves under the Northwest Forest Plan (NWFP) and the Shasta-Trinity National Forest Land and Resource Management Plan (Forest Plan), as it lies within 300 feet of a fish-bearing perennial stream (Conner Creek). One acre of the proposed project area (Conner Creek Road staging area) is outside of Riparian Reserves, but all proposed project activities will meet the Aquatic Conservation[CJordan6] Strategy Objectives. Additional details regarding application of all applicable environmental laws and regulations are provided in Section IV below.

The proposed project would remove the 10-foot diameter corrugated metal culvert at Red Hill Road (Crossing #2) and replace it with an 18-foot wide, embedded metal plate arch culvert. It would also remove the 18-foot long, 6-foot tall, 14-foot wide concrete box culvert at Conner Creek Road (Crossing #1) and replace it with a 24-foot wide by 7-foot tall bridge (14-foot wide travel way). Specific information for each Crossing is provided below.

Red Hill Road (Crossing #2): The existing 10-foot diameter, 66-foot long corrugated metal (CMP) culvert would be replaced with an embedded 18-foot wide, 12-foot tall, 70-foot long multi-plate arch culvert set at a maximum 5% gradient (refer to Figure 4 for a similarly designed project in the Junction City area). The new stream crossing gradient would be consistent with the average channel gradient in the area of 5%. The project would not require the installation of headwalls, flared inlets/outlets or other inlet/outlet controls, except for minor rock slope protection (RSP). This design minimizes the disturbance to riparian vegetation outside of the road fill prism during construction. The increased road width could eliminate the need for guard rails (to be determined by DOT engineering staff).


Figure 5. Red Hill Road Crossing (#2)

A Bailey bridge would be installed over the crossing once the road base and portion of the roadfill material are excavated to allow for installation. The Bailey bridge will allow for full excavation of the remaining roadfill, existing culvert and remaining construction activities while providing for one-way traffic throughout construction. The excavation is expected to be approximately 22 feet wide at the bottom and approximately 60 feet wide at the top and 70 feet long, with an average 12-foot depth. Approximately 740yd3 of material would be excavated. The multi-plate arch structure would be assembled within the excavation area and approximately 460yd3 of fill would be reincorporated into the roadfill after the new structure is constructed. The roadfill slopes would be at reconstructed at the same angle as the existing fill (1½:1). Spoils material would be stored the existing open, flat staging areas for re-use in the project. Any excess material (~280yd3) would be stored at a pre-approved disposal site or recycled at a DOT yard. All material will be stored in a manner to not deliver to a watercourse.

Approximately 20% (or 2 feet) of the bottom of the new arch crossing (~85yd3) would be embedded with D5-D85 particle size engineered stream channel mix and a low flow channel would be shaped within the crossing floor. The engineered streambed will be placed, the low flow channel shaped and the bed jetted to seal the voids in the streambed material. Rock weirs/ribbons may be installed within the crossing to define the low flow channel and provide grade control at 5%. A rock ribbon consisting of 1 to 2 ton boulders would be set in the existing outlet pool for grade control and the pool would be backfilled with engineered streambed mix and sealed. The rock ribbon would be set 6 inches below the designed streambed elevation. The channel gradient from the downstream control point (tailwater control for the outlet pool) to above the upstream rock ribbon would conform to the average 5% channel gradient in this reach.

The new crossing would span the 12 to 14-foot active channel width as well as the 2-year channel width, but would not have a 1:1.5 ratio associated with a stream simulation design project. The current crossing (~79ft2 surface area) can convey less than the 20-year flow before it backwaters and requires active management for removal of large wood debris accumulation at the inlet. The road overtops on the 43-year flow and the new design (~144 ft2 surface area) would convey the 100-year recurrence interval flow and provide for more efficient transport of bedload and debris.

While stream and groundwater dewatering would not be necessary during excavation of the roadfill material (initial construction phase), surface water re-routing and groundwater seepage controls would be installed during the subsequent removal of the existing metal culvert, installation of the multi-plate arch, excavation and placement of two sub-grade grade control boulder ribbons and placement of the engineered stream bed material. Dewatering and fish exclusion fencing placement would be conducted consistent with BMPs and species relocation would be conducted by a qualified fisheries biologist. Fish, if present, would be relocated to areas both upstream and downstream of the fish exclusion fencing (for complete details on fish exclusion fencing installation and location and channel reach dewatering, refer to the project Fisheries Biological Assessment and Evaluation). Channel dewatering should only be necessary for 3 to 4 weeks.

Approximately 37 sapling sized trees (<1” diameter), 24 small trees (1” to 6” diameter), 12 medium sized trees (6” to 12” diameter) and two larger big leaf maples (19” and 22” diameter) would be removed from the road prism. Cores from two trees indicate that the older trees in the road prism are approximately 50 years old. Trees to be removed include white alder, big leaf maple, madrone, ponderosa pine, incense cedar and Douglas fir. Other shrub/ground species to be removed from the road fill include wild grape, English ivy, poison oak and small amount of native and non-native grass species. After installation of the new crossing, replacement of theroadfill and shaping of the fillslopes native grass seed and shrubs/tree species would be planted and mulched with rice straw, ground wood mulch or similar suitable weed-free mulch material. Portions of the fill face would be armored with RSP and/or cobble-sized material. Interim slope erosion control techniques such as silt fencing and large wood placement would be utilized on fill slopes (refer to BMPs in Section V).

Conner Creek Road (Crossing #1): The existing 6-foot tall, 14-foot wide, 18-foot long concrete box culvert would be replaced with a pre-fabricated 7-foot tall, 16-foot wide, 40-foot long steel beam bridge. The freespan width would be 24 feet, more than 1.5 times the active channel width of the reference reach. The surface area of the new crossing floodplain is ~156 ft2 compared to the 70 ft2 floodplain of the existing opening. HEC-RAS[2] modeling indicates that the crossing would be able to convey the 100-year peak flow (1,806 cfs) while the existing box culvert overtops at less than the 25-year recurrence flood interval (885 cfs). Removing the offset baffles would reduce the potential for debris accumulation within the crossing. The left bank would be in the current location of the existing wingwall. The right bank would be excavated back sufficiently to widen the active channel width to 24 feet and provide clearance for placing the new abutment. The new abutments would be 7 feet tall, 1 foot wide and 16 feet long. These abutments would sit on a 3-foot wide footing placed on a 6-foot deep concrete keyway that is set below the maximum scour depth.

Figure 6. Conner Creek Road (#1)

All excavation would be within the road prism and its associated toe slope. A “V” shaped low flow channel would be formed using D5-D85 sized engineered streambed material that would have a 1-foot drop from the edge of each stream bank to the center of the channel; representing an approximate 8.5% stream bank gradient. The low flow channel would not conform to the riffle and run habitat immediately upstream, but would maintain fish passage during low flows.

A detour bridge would be placed adjacent the existing roadway/culvert on the downstream end and the approaches will conform to the road shoulders. Minor rock placement would be placed to transition the approaches. Three alder trees may need to be trimmed or removed due to overhang near the existing culvert but if retention is deemed safe and feasible, every effort to retain all or the majority of the trees will be made. It is anticipated that the detour bridge would be needed for 1 to 2 weeks. There are no underground or overhead utilities to be relocated.

After aquatic species relocation, temporary bridge and stream diversion (clean water bypass) installation, the 3-foot wide, 6-foot deep, 16-foot long concrete footing (keyway) will be formed and placed in the existing roadway directly behind the existing culvert’s left bank abutment (abutment will be left in place as a support wall). This work will be completed outside of the active channel and there should be limited potential for ponding of groundwater and delivery of roadfill material to the stream. A 1-foot wide, 7-foot tall, 16-foot long abutment will be formed/placed atop the footing. A similar sized footing and abutment will be excavated and constructed on the right bank. This will also require excavation of the material between the right bank footing/abutment and the existing culvert (~120yd3). Once the footings and abutments have cured, structural backfill will be placed (~40yd3) to fill the voids behind the abutments and compacted with a manual whacker and/or other small equipment to compaction specifications. The box culvert will be left in place for the duration of footing excavation/placement and abutment construction. Once cured, the culvert will be excavated (with exception of the left bank abutment) and removed to the equipment staging area or DOT yard. Partially grouted rock slope protection (¼ to ½-ton boulders) will be placed at a 1:1 slope along the left bank wing wall for stabilization and scour protection. Engineered streambed material (D5-D85 size) will be placed and jetted to compaction in the crossing to form a low-flow channel (~20yd3), providing for fish passage at low flows. A rock-ribbon grade control structure (1 to 2-ton) will be installed 6” below the designed streambed elevation in the outlet pool area (already e-fished and dewatered). The outlet pool will be backfilled with D5-D85 sized streambed mix (~23yd3) and jetted to compaction. A similar grade control structure will be installed immediately upstream of the crossing. The rock slope protection/ribbons and streambed will be installed from the roadway using an excavator or other heavy equipment. After placement of all RSP and grade control, the pre-fabricated bridge deck will be set with a crane.

Dewatering would be necessary during excavation of the left wingwall, pouring of the left keyway and footing, during demolition of the box culvert, excavation and placement of the two grade control structures and construction of the new stream channel. Installation of fish exclusion fencing, species relocation and dewatering would be consistent with BMPs. Channel dewatering would be necessary for 1-2 weeks.

Guardrails would be installed prior to removal of the detour bridge. Paving would be completed at a later date. The entire construction window is estimated at 8 weeks.

II. Field Evidence

Conner Creek Watershed Scale

Conner Creek is a fourth-order perennial tributary to the Trinity River that flows through moderately steep terrain in a northeasterly direction. Elevations range from 1,450 feet at the mouth to 5,507 feet northeast of the Hayfork Divide. The majority of the watershed is within the Eagle Inventoried Roadless Area, with the lower part of the watershed located in rural residential areas of Junction City. Extensive mining activity in the lower reaches of Conner Creek modified the historic channel and altered conditions at the confluence with the Trinity River.

A Stream Condition Inventory (SCI) survey was completed by the USFS fisheries staff on a 2,290 foot reach upstream of Crossing #2 in 2007 (SCI records, Weaverville Ranger District). The 2007 SCI located 36 pieces of large woody debris (LWD) in the survey reach (equates to 83 pieces of LWD/mile). All pieces were at least 16” dbh[CJordan7], but only three were ≥ 50 feet in length (indicating non-functioning LWD recruitment). It is anticipated that LWD recruitment will increase over the next decade as a result of the Eagle Fire and the existing crossings on Red Hill and Conner Creek Roads presently require the removal of larger LWD from the channel to avoid plugging the culverts.