1 Floodplain Management SESSION 7 Stream Systems on Dynamic Earth Floodplain Management Principles & Practice Prepared By Donald R. Reichmuth, PhD.

2 Management Framework Objectives: 1Stream sediment cycle in terms of source, transport and deposition. 2Difference between the engineering and geologic approaches in developing analytical tools for stream management. 3Channel blockages and overall stream stability. 4Behavior and stabilization methods used in drainages showing vertical instability. 5Problems associated with horizontal stream channel migration. 6Management practices to determine how to insure low impact development. 7 Present floodplain as a product of the geological floodplain -- case study exercises 8 Module 2 examination.

3 Elements Of Channel Formation

4 Analytical Methods Engineering Approach Initiated By Irrigation Designers Mathematical Approximations Equations Have Limited Utility Geologic Approach Initiated By Field Explorers Descriptive Physical Principals Universal Concepts Developed

5 Energy Equations Note: Extra Friction Loss For Expanding Sections

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7 Stream Problem Types Channel Blockage In-channel Obstructions Geologic Accidents Impoundments Vertical Change Headcutting Channel Aggradation Horizontal Change Meander Loop Migration Bank Erosion Channel Cutoffs

8 Channel Blockages Blockages can vary in size from a single downed tree to total channel filling.

9 Effects Of In-stream Obstructions

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11 Debris Flow Example Amero, Colombia

12 Regional Uplift Erosion Patterns Note: Colorado River Maintained Original Grade

13 Cross Section View Note: Grand Canyon Formed At Top Of Structural Warping

14 From Canyons of the Colorado By J. W. Powell 1895

15 Erosion Patterns Note: Stream Gradient Maintained During Tectonic Uplift

16 Effects Of Dams

17 Colorado River Hydrograph Below Lake Powell

18 Clean Water Releases From Lake Powell -- Nov. 2004

19 Typical Fish Passage Problem Note: The Extreme Turbulence At The Base Of The Structure

20 Typical Concrete/ Steel Design Yakima River -- Town Diversion U.S. Bureau of Reclamation Design Age About 15 Yrs. Drop Height About 6 Feet Fish Ladder Cells (5 Drops) Repair Costs $200,000 Est. ($130,000 Spent) Other Problems Apron Undercut

21 Irrigation Diversion Dam Typical Concrete Structure With Fish Ladder

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23 Improved Safety

24 Fish Passage Proof

25 Vertical Change The sediment availability causes most channel filling and degradation. Many regions are experiencing downcutting as earlier glacial deposits are mobilized.

26 Headcuts – Cause & should we do anything?

27 Headcut-Caused Failure Open Arch Culvert --- Bed Scoured To Bedrock

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29 Vertical Grade Stabilization Excess Energy Removed With Drops

30 Rock Drop Characteristics Stable Fish Friendly Overhead Cover Low Velocity Eddy Macro-Invertebrates Safe For Boaters Unstable Poor Habitat Standing Wave Unsafe

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32 Rock Drop Example Low Flow Concentrated At Mid-Channel

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34 Horizontal Change Horizontal channel migration is most common in regions that have low stream gradients and have reached an equilibrium grade.

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37 Meander Loop Cutoff Loss Of Energy Dissipation Must Be Replaced For Stable Conditions To Exist

38 Bank Erosion Caused By Uncontrolled Upstream Sediment Source

39 Cumulative Impacts Low Impact Development can only occur when long range goals are adopted that minimize cumulative impacts.

40 Quick Flush Poor Management Technique Shifts Problems To Others Encourages Unsound Development

41 Floodplain Utilization Good Management Technique Helps Protect Downstream Reaches Increases Base Flow Encourages Sustainable Development

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43 Cumulative Impacts On Roaring Fork River Floodplain

44 Roaring Fork River 1985 Aerial View Before Highway Construction

45 Roaring Fork River Aerial View Of Bottleneck Area

46 Roaring Fork River Ground Photo Showing Failing Gabion Basket Wall

47 Slide Presentation Prepared By Geomax, P.C. Dr. Donald R. Reichmuth, President 1023 W. 30 th Ave. Spokane, WA Phone & FAX – –