Presentation on theme: "1 Floodplain Management SESSION 7 Stream Systems on Dynamic Earth Floodplain Management Principles & Practice Prepared By Donald R. Reichmuth, PhD."— Presentation transcript:
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
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
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
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
32 Rock Drop Example Low Flow Concentrated At Mid-Channel
34 Horizontal Change Horizontal channel migration is most common in regions that have low stream gradients and have reached an equilibrium grade.
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
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