Lower Lemhi River Project Reach SubReach 4 SubReach 3 Sub Reach 2 - - PowerPoint PPT Presentation

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Nov 10, 2022 298 likes •610 views

Lower Lemhi River Project Reach SubReach 4 SubReach 3 Sub Reach 2 SubReach 1 Lemhi Basin Historical Broad Fertile Valley Perspective Wide Vegetated Floodplain Complex Anabranching Channel Lemhi River

SLIDE 1

Lower Lemhi River Project Reach

Sub‐ Reach 2 Sub‐Reach 4

Lemhi Basin

Sub‐Reach 3

Sub‐Reach 1

SLIDE 2

Broad Fertile Valley
Wide Vegetated Floodplain
Complex Anabranching Channel

…. he found the weir extended across four channels of the river which was here divided by three small islands…..

First recorded historical observation of Lemhi Shoshone‐Bannock Fishing (Journals of the Lewis and Clark Expedition, Moultin 1998)

Historical Perspective

Lemhi River

Reference to Anabranched Watershed

SLIDE 3

Historical Perspective

Lower Lemhi Mainstem

Productive Salmon Habitat to mouth of Lemhi

Gebhards 1958

Project Location

SLIDE 4

Railroad was removed in 1939, and transferred to the State of Idaho 1952. The highway engineers preferred to “move the river” rather than construct the many bridges required.

Historical Perspective

Lemhi Channelization

SLIDE 5

Historical Perspective

Lemhi Channelization

Gebhards 1958

SLIDE 6

Historical Perspective

Current Lemhi Floodplain

Agricultural Development

SLIDE 7

Anabranched Channel

Configuration

Sinuosity
Expansive Floodplain

Historical Perspective

Current Lemhi Floodplain

SLIDE 8

Agricultural Development

Historical Perspective

Current Lemhi Floodplain

SLIDE 9

Lemhi Chinook Salmon

Life Stage Specific Distribution

Lemhi RST

Spawning Upper River/Hayden
“Early” Parr

Fry Displacement (20 – 45k) ‐ Hayden Creek ‐ Upper Lemhi Adult Production Early Migration

SLIDE 10

Lemhi Chinook Salmon

Life Stage Specific Distribution

Lemhi RST

Juvenile outmigration

50 100 150 200 250 300 Total Captured Date

2011 Hayden Cr Screw trap ‐ Chinook

Fry

SLIDE 11

Life Stage Specific Capacity – Lemhi Summer Parr

SLIDE 12

500,000 1,000,000 1,500,000 2,000,000 Number of Summer Parr

Lemhi Winter Presmolt Capacity

Available (QRF) Contemporary (Mean) Contemporary (Max) MAT MAT + 25%

Life Stage Specific Capacity – Lemhi Summer Parr

SLIDE 13

Project Updates; Sub‐Reach 2

SLIDE 14

Watered 1750’ Side Channel
5 Engineered Log Jams
375’ Bank Roughening
15 Habitat Structures

Channel Inlet

Channel

Project Updates

Sub‐Reach 2

ELJ

* 2016 Completion

SLIDE 15

Project Updates

Sub‐Reach 3

SR3‐Section 2 SR3‐Section 1 Lower Upper

Excavate Floodplains and Channels
Raise Surface Water Elevations at Channel Inlets
Install Substantial Wood Structures

SLIDE 16

SR3 – Section 1 Pre Construction

SLIDE 17

SR3 – Section 1 Construction

2017 2018

SLIDE 18

SR3 Construction

Spring 2018 Fall 2018 Fall 2018 Ongoing

SLIDE 19

Project Updates

SLIDE 20

Lidar Elevation Data

Stokes Ranch Flooding

SLIDE 21

Stokes Ranch

Prior Scour and Erosion 1992

SLIDE 22

Stokes Ranch

Prior Scour and Erosion 2014

SLIDE 23

Stokes Ranch

IDFG Bank Treatment

SLIDE 24

Stokes Ranch Flooding 2017

Riprap

SLIDE 25

Flooding 2018

Riprap

SLIDE 26

Flooding 2018

Riprap

Bridge

SLIDE 27

Flooding 2018

SLIDE 28

Temporary Flood Control

IDFG Supported
Collaborated with

Lemhi County

Reduced Overland

Flooding

SLIDE 29

Temporary Flood Control

Completed Coffer Dam

SLIDE 30

Habitat Goal – Improve habitat capacity by increasing floodplain interaction and channel complexity

Develop lateral floodplain habitat/anabranched channels
Improve mainstem stream sinuosity
Add complexity (LWD) side channel/mainstem
Develop floodplain interaction

Project Goals and Objectives

Objectives Phase I – May 2019 Implementation Phase 2 – 2020 Implementation

Install bioengineered structures (LWD) to add habitat

complexity while stabilize eroding banks ‐ control downstream flooding

Incorporate structures into Phase 2