217217217

200200200

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163163163

131132122

2396553

110135120

1129256

62102130

1025648

130120111

237237237

8011927

252174.59

“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”

Prepared by Scott Pozarycki9 August 2018

HOWARD A HANSON DAM

Water Management and Natural Resources

1

2Green River Watershed

HAHD Purposes

Flood Risk Reduction is primary mission– 104k acre-feet of authorized flood storage; 1962

Fish Conservation– 24k ac-ft stored for low flow augmentation; 1962

Section 1135 ecosystem restoration project– 5k ac-ft stored for low flow augmentation; 1997– Tacoma is local sponsor

Water supply – Additional Water Storage Project– 20k ac-ft; 2007– Tacoma is local sponsor

3

Required Flood Storage Capacity4

1 Oct10 May

1 Nov20 Feb

Spring Water Storage And Allocation5

Fish Conservation

Goal: maintain minimum of 110 cfs at the Palmer stream gage (98% reliability)

– Protects against late fall drought– Requires capture and storage of 24k ac-ft– Water released/conserved based on guide curve to

meet this goal– Minimum discharge from the dam would be based on

the 110 cfs flow target plus the Tacoma first diversion water right claim (113 cfs or reservoir inflow, whichever is least)

6

Fish Conservation Refill and Guide Curve 7

20 Feb1 Dec

1 June

Section 1135 Ecosystem Restoration

Objectives: – Capture 5k ac-ft during spring refill– Release water to achieve maximum benefits as

determined by the Green River Flow Management Coordination Committee

Adaptive management alternative– Storage and release is adaptively managed based on

hydrologic conditions, natural resources, regulatory considerations, other factors – flexibility is key

– Project sponsor is Tacoma

8

Water Supply for Tacoma

Additional Water Storage Project (Phase 1) – Authorized by Congress in 1999– Corps captures and stores 20k ac-ft for Tacoma use– Tacoma determines release schedule– First captured and stored in 2007– AWSP phase 1 not yet fully implemented; 50% of water

being used to benefit fish resources in the interimPhase 2 water storage of additional 12k ac-ft potentially in the future

9

Green River Flow Management Coordination Committee

Biweekly conference calls during the refill and augmentation period (late Feb to Nov)

Any agency/individual can participate

Discussion of environment & resource conditions, water supply, water needs

Develop capture & release strategy; adjust in real time as needed

Provides recommendation to Corps - goal is to achieve consensus on path forward

10

Spring Refill ObjectivesCapture and store 49k ac-ft for all purposesAdaptively capture water minimizing impacts to natural

resourcesMaintain natural character of the hydrograph downstream

of the dam by capturing percentage of total flow Capture strategy considerations include:

– Status of snowpack, rain storms– Juvenile salmon emigration, habitat– Instream flows, side channel connection flows– Steelhead spawning– Opinions of the GRFMCC

11

Typical Augmentation ObjectivesEnsure instream minimum flows

– 110 cf at Palmer stream gage (Corps fish conservation authority)

– 250 cfs at Auburn stream gage (GRFMCC objective; Tacoma requirement under their HCP, MIT agreement); 225 cfs if declared drought

Protect steelhead redds, minimize dewateringMaximize summer rearing habitat (steelhead, coho)Support Chinook salmon adult migration and spawning

12

Operation In 2016 – Average Water Year

reservoir

HAHD outflow

HAHD inflow

2016 Flow at Auburn stream gage– with and without flow augmentation

with flow augmentation

without flowaugmentation