Floodplain Management SESSION 7

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Floodplain ManagementSESSION 7

• Stream Systems on Dynamic Earth
• Floodplain Management
• Principles Practice
• Prepared By
• Donald R. Reichmuth, PhD.

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Management Framework

• Objectives
• 1 Stream sediment cycle in terms of source,
  transport and deposition.
• 2 Difference between the engineering and geologic
  approaches in developing analytical tools for
  stream management.
• 3 Channel blockages and overall stream stability.
• 4 Behavior and stabilization methods used in
  drainages showing vertical instability.
• 5 Problems associated with horizontal stream
  channel migration.
• 6 Management 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.

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Elements Of Channel Formation
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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

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Energy EquationsNoteExtra Friction Loss For
Expanding Sections
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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

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Channel Blockages

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

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Effects Of In-stream Obstructions
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Debris Flow ExampleAmero, Colombia -- 1985
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Regional Uplift Erosion PatternsNote Colorado
River Maintained Original Grade
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Cross Section ViewNote Grand Canyon Formed At
TopOf Structural Warping
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FromCanyons of the ColoradoByJ. W.
Powell1895
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ErosionPatternsNoteStream GradientMaintained
During Tectonic Uplift
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Effects Of Dams
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Colorado River HydrographBelow Lake Powell
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Clean Water ReleasesFrom Lake Powell -- Nov. 2004
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Typical Fish Passage ProblemNoteThe Extreme
Turbulence At The Base Of The Structure
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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 ---------- 4 Cells (5 Drops)
• Repair Costs --------- 200,000 Est.
• (130,000 Spent)
• Other Problems ----- Apron Undercut

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Irrigation Diversion DamTypical Concrete
Structure With Fish Ladder
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Improved Safety
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Fish Passage Proof
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Vertical Change

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

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Headcuts Cause should we do anything?
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Headcut-Caused FailureOpen Arch Culvert --- Bed
Scoured To Bedrock
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Vertical Grade StabilizationExcess Energy
Removed With Drops
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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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Rock Drop ExampleLow Flow Concentrated At
Mid-Channel
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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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Meander Loop CutoffLoss Of Energy
DissipationMust Be ReplacedFor Stable
Conditions To Exist
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Bank ErosionCaused By Uncontrolled Upstream
Sediment Source
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Cumulative Impacts

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

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Quick FlushPoor Management Technique Shifts
Problems To OthersEncourages Unsound
Development
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Floodplain UtilizationGood Management
TechniqueHelps Protect Downstream
ReachesIncreases Base FlowEncourages
Sustainable Development
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Cumulative ImpactsOn Roaring Fork River
Floodplain
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Roaring Fork River1985 Aerial View Before
Highway Construction
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Roaring Fork RiverAerial View Of Bottleneck Area
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Roaring ForkRiverGround PhotoShowingFailing
Gabion BasketWall
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Slide Presentation Prepared ByGeomax, P.C.Dr.
Donald R. Reichmuth, President1023 W. 30th
Ave.Spokane, WA 99203-1324Phone FAX
509-838-6390E-mail geomax_at_comcast.net