Pierce County Upper Nisqually Protection & Stabilization Project

Mount Rainier National Park –Upper Nisqually Protection and Stabilization Project

Ingo Kuchta - Project Manager/EngineerBrian Bennett - EngineerMarty Ereth - BiologistRob Wenman - Planner

Pierce County Surface Water Management

November 17, 2017

. .

Problem Statement: Reoccurring damage to the existing levee structure during high flows.

– Location – Nisqually River: Right Bank

(near Nisqually gate main entrance to Mt. Rainier National Park)

– What is at Risk? – Mount Rainier National Park access and utility infrastructure. Nisqually Park Subdivision

– Proposed Project or Action - Construct a series of 28 rock deflectors

Project Overview

11/17/2017 MRNP– Upper Nisqually Protection and Stabilization Project

Why is protection and stabilization necessary?

To protect critical infrastructure and maintain access to the Mount Rainier National Park

Protect the Nisqually Park Subdivision downstream

Substantially reduce reoccurring repair costs associated with damaging floods

Project Overview

MRNP– Upper Nisqually Protection and Stabilization Project11/17/2017

Maintenance Costs

11/17/2017

Note:

Costs do not factor in

today’s costs

MRNP– Upper Nisqually Protection and Stabilization Project

YEAR PIERCE COUNTY USACE

1991 $ 74,610

1992 $142,718

1993 $217,000

1995 $ 50,000* $200,000

1996 $ 50,000* $200,000

2003 $122,500

2004 $203,000

2005 $131,000

2006 $900,760

2010 $529,500

2011 $185,629* $752,529

2012 $652,655

2017 $243,440* 973,800

Subtotal $3502,812 $2,126,329

TOTAL $5,629,141

* County share is typically min. 20% of total cost

Levee/Revetment

Repair Costs

Since 1990

Reach Characterization – Glacial Fed


Project

Site

Reach Characterization - continued

11/17/2017

• Contributing basin is 65 square miles

• Mostly within Mt. Rainier National Park

• Relatively undeveloped

• 80 inches of rain annually (avg.)

• Short duration runoff/steep gradient

• Large amounts of sediment transport

• Sediment drives channel thalweg.


Reach Characterization


Nisqually Levee

Na

tio

na

l P

ark

Bo

un

da

ry

Reach Characterization - continued


Braided river

channel

High bench

terraced

floodplain

Lahar deposit/

old growth

forest

Levee

structure

Mt. Rainier

National Park

Sunshine Point

Campground

Reach Characterization


2006 flood event


2006 flood event

11/17/2017

• Sunshine Point Campground and entrance road to Mt Rainier National Park washed out.

• Major damage to roadways, buildings and infrastructure.


Source: MNRP

2006 flood event


Source: MNRP

2006 flood event


Ongoing repairs 2006- present


2011

Repair

USACE

Ongoing repairs 2006- present


2012 Repair

(Pierce County)

River Diversion Plan - 2012


Existing Conditions – flow velocity


Existing Conditions 9580 cfs

ELJ Proposed Alternative

11/17/2017

• Construct a series instream engineered logjam structures (ELJ) to encourage sediment deposition in the washout area and lower water velocities. Additional deflector structures could be built along the revetment face as part of a second phase.

• Desired effect was to encourage the thalweg to move away from the revetment.

• Reduce water velocity around the logjam and revetment face encouraging sediment deposition.


ELJ Alternative


ELJs

Mt. Rainier

National Park

Flow Velocities with ELJs


Conditions After ELJs Construction 9580 cfs

ELJs

ELJs in updated flow model


ELJs

Deflector alternative


Deflector

structures

• 4,760 feet of levee treated

• 28 structures

• Sized: approx. 80 ft. x 30 ft P

ark

boundary


Deflector alternative – plan view


Deflector alternative – x-section

Flows- Existing vs Deflector alternative


Deflector alternative – Flow Model


Deflector alternative – flow model


Permits:• Pierce County – Shoreline conditional use permit, SEPA review

(submitted Jun. 2017)

• WDFW – Hydraulic Permit (HPA) (Jan. 2018)

• Ecology – Section 401 Water Quality Cert. (Jan. 2018)

• USACE – Section 404 Individual Permit (Jan. 2018)

• National Park Service – Construction Permit, NEPA review




9/15/2015

Questions?


Pierce County Upper Nisqually Protection & Stabilization Project

Environment

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