Tailrace Slough Instream Flow Study Packwood Lake Hydroelectric - - PowerPoint PPT Presentation

Tailrace Slough Instream Flow Study

Packwood Lake Hydroelectric Project Fish/Aquatics Subcommittee Meeting December, 2006

Slough Below Project Tailrace

• Tailrace Slough (TS) is used by anadromous

salmonids in the spawning life stage:

– Chinook Salmon (Observed) – Coho Salmon (Observed) – Steelhead Trout (Potential) – Cutthroat Trout (Potential)

• Flows and Habitat in the TS are affected by:

– Cowlitz River Flows – Project Operational Flows – Project Operations

Slough Below Project Tailrace (cont’d)

• Project Operations Have the Potential to

Impact Spawning Habitat in TS

– Project has shut down annually for maintenance in October. This can potentially impact redds in the TS.

Cowlitz River and TS are Dynamic

• 2004

Tailrace Slough completely dependent upon Project flows, except at very high Cowlitz River flows

• 2005

Floods in Dec 2004/Jan 2005 reconfigured TS and TS was mostly dependent upon Cowlitz River flow (20% of Cowlitz R in TS)

• 2006

Floods in Jan 2006 again reconfigured TS.

– More dependent upon Project Flows, esp. at Low Flows – Cowlitz R contributes 13% ONLY when Cowlitz R Flows > approximately 625 cfs.

• Floods in November 2006 again reconfigured TS,

with Cowlitz River now contributing more flow.

• 1.96

41.04 43 604 3/23/2006 2.52 44.52 42 650 3/28/2006 20.29 79.89 59.6 843 3/9/2006 12.28 87.28 75 823 2/23/2006 44.05 88.85 44.8 1040 4/6/2006 68.266 112.866 44.6 1260 4/12/2006 122.13 242.23 120.1 1540 2/9/2006 Cowlitz R Contribution (cfs) Tailrace Slough Flow (cfs) Plant Flow (cfs) Cowlitz R Flow (cfs) Date

Contribution of Cowlitz R to Tailrace Slough (cfs)

• 20

20 40 60 80 100 120 140 200 400 600 800 1,000 1,200 1,400 1,600 1,800 Cowlitz R Discharge Contibution to Tailrace Slough

r2 = 0.9746

Tailrace Instream Flow Study

• Project Area: Immediately downstream of

Project tailrace downstream to confluence with the Cowlitz River. Includes

– Main Channel Below Tailrace (Transportation and Spawning) – Right Channel (Transportation) – Left Channel (Transportation and Spawning)

T Tailrace Slough and Cowlitz River (1996)

Instream Flow Study Issues

• How much habitat is available for anadromous

salmonids in the TS for:

– Chinook Salmon Spawning – Coho Salmon Spawning – Steelhead Trout Spawning

• During what time periods are redds most

vulnerable to dewatering?

• What impact does Project operation have on

potential redd dewatering?

• What role can the Project have in protecting

redds in the TS?

TS Spawning Habitat

• Geomorphology Studies currently

underway to map and quantify spawning substrates in TS

• Transects have been selected to address

spawning habitat in:

– Main channel, TS – Left side channel, TS

• These transects will be used to model

habitat and assess dewatering risk

Trans 8 Trans 7 Q Meas Q meas Trans 5 Trans 6

Trans 4

Trans 3 Trans 2 Trans 1

Transects

• Transect 1: Glide w/lateral pocket water
• Transect 2: Riffle below Split Channel
• Transect 3: Split Channel Run (LB larger)
• Transect 4: Split Channel Run (RB larger)
• Transect 5: Pool
• Transect 6: Spawning Riffle/Run on L Side

Channel approx. 50 yards DS of confluence w/Main channel

• Transect 7: Main channel glide
• Transect 8: Plunge pool/run below tailrace

Tailace IFIM Measured Flows

50 100 150 200 250 300 350 400 450 500 Left Channel Right Channel Mainstem Discharge (cfs)

Tailrace Low Flow

Tailrace Middle Flow

Tailrace IFIM – High Flow

November 2006 Flood

November 2006 Flood

Can you see the pool in this picture?

How ‘bout now?

CAVEATS

• Channel is dynamic and subject to change

– sometimes annually

• Results will not provide “the Answer” since

the channel is changing all the time

• Result will provide a “Snapshot” of how

habitat will respond to differences in flow – given the configuration that is measured and modeled at the time.