217217217
200200200
255255255
000
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