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Integrated Design. Key engineering concepts Conveyance, capacity of the channel to move water Reliability, capacity of the system to maintain itself and function without breakdown Safety, ability to avoid hazards and recover from upsets.

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integrated design
Integrated Design
  • Key engineering concepts
    • Conveyance, capacity of the channel to move water
    • Reliability, capacity of the system to maintain itself and function without breakdown
    • Safety, ability to avoid hazards and recover from upsets
linking conveyance and reliability to restoration and enhancement
Linking Conveyance and Reliability to Restoration and Enhancement
  • Plant response to flows
    • How plants “react” to flow, how they steer flow
  • Modeling flood flows
    • How looking at roughness as a dynamic parameter changes the equation
  • Failure modes
    • Erosion
    • Overtopping, cracks, holes
  • Separating people from danger
plant water interactions
Plant-Water Interactions
  • Plant species
  • Branch density
  • Rigid/flexible/bending
  • Emergent/submerged
  • Scale
  • Plant scale/stand-reach
  • Leaf area index (LAI)
emergent submerged
Emergent/Submerged
  • Engineers love equations…..
slide6

Rigid/Flexible/Bending

  • Recent research with field tests of bending.
  • Modulus of elasticity estimated for tree species; natural materials exhibit high variability.

From: Stone et al (2013)

slide7

Rigid/Flexible/Bending

  • Bending characteristics estimated for flow velocities using vegetation-bending algorithm.
  • Results provide approach for predicting bending behavior; i.e., “dynamic” hydraulic roughness.

From: Stone et al (2013)

energy losses from vegetation
Energy Losses from Vegetation
  • Plant geometry
  • Topology
  • Age
  • Seasonality
  • Foilage
  • Volumetric/areal porosity
  • Density
  • Patchiness
hydraulic roughness
Hydraulic Roughness
  • Past – one value for entire floodplain, plants increase roughness
  • Current – multiple values for parts of floodplains, plants affect roughness +/-
  • Emerging – dynamic values accounting for velocity and depth, plants used to place roughness
variations in hydraulic roughness
Variations in Hydraulic Roughness
  • Channel-floodplain hydraulic geometry
  • Flow depth and plant height
  • Plant age
hydraulic roughness variations with hydraulic geometry
Hydraulic Roughness - Variations with Hydraulic Geometry
  • Depth in Channel and Floodplain

From Chow (1959)

hydraulic roughness variations with hydraulic geometry1
Hydraulic Roughness - Variations with Hydraulic Geometry
  • Shearing effects and resistance from vegetation and topography slow floodplain overflows.
  • This, in turn, causes a reduction in the velocity of the flow in the main channel also and leads to a point when channel-floodplain storage is optimized.
floodplain storage optimization
Floodplain Storage Optimization
  • Independent research indicates channel-floodplain storage is optimized when average channel and floodplain velocity is minimized at depth ratios of 1.2 > D/Dc > 1.6, where D = flood depth and = Dc bankfull depth.

D= 19-feet

Dc= 16-feet

D/Dc = 19/16 = 1.2

From: Bhowmikand Demissie, 1982

hydraulic roughness variation with flow depth and plant height
Hydraulic Roughness – Variation with Flow Depth and Plant Height
  • Hydraulic resistance varies with canopy height (CH) and foilage/branch density (FD).
  • Conceptually, as plants submerge roughness decreases from FD value to near novegetation (NV) value.
  • This neglects understory complexity, bending, etc.

From: Anderson et al (2006)

hydraulic roughness variation with flow depth and plant height1
Hydraulic Roughness – Variation with Flow Depth and Plant Height
  • Four plant scenarios modeled using NWS FLDWAV (1D); 0.0m, 0.5m, 1.5m, 3.0m.
  • Bare earth n=0.043 and maximum n=0.150.
  • Weighted average approach of horizontal “slices” defined roughness variation with depth.

From: Anderson et al (2006)

hydraulic roughness variation with flow depth and plant height2
Hydraulic Roughness – Variation with Flow Depth and Plant Height
  • Q2 and Q100 flood waves routed 60 km.
  • Peak flow attenuation greater for Q100 .
  • Rising limb flattens more for Q2 with more peak flow lag in various plant scenarios.

From: Anderson et al (2006)

hydraulic roughness variation with vegetation community age
Hydraulic Roughness – Variation with Vegetation Community Age
  • For the same flood stage, plants present a different hydraulic resistance during their life cycle – not addressed much in the literature!

n2>n3>n1

n1

n2>n1

Colonization

Juvenile

Old Age

floodplain definitions
Floodplain Definitions
  • Hydraulic floodplain - “The surface next to the channel that is inundated once during a given return period regardless of whether this surface is alluvial or not.”

(Hydraulic Engineering Centre, 1976; Ward, 1978)

  • Genetic floodplain - “The largely horizontally-bedded alluvial landform adjacent to a channel, separated from the channel by banks, and built of sediment transported by the present flow-regime.”

Nanson and Cooke (1992)

  • Polyphase floodplain – “The product of secular climate or other environmental (e.g. base level or land use) change.”

Nanson and Cooke (1992)

floodplain evolution
Floodplain Evolution
  • Floodplain terraces.

From: Leopold et al (1992)

floodplain evolution1
Floodplain Evolution
  • Natural levees.

From: Greenfieldgeography – Floodplain Mangement (2013) http://greenfieldgeography.wikispaces.com/Floodplain+management

slide22

Update with Central Valley example

From: Cook Inlet Wetlands (2013) http://www.kenaiwetlands.net/EcosystemDescriptions/Riparian.htm

floodplains and groundwater
Floodplains and Groundwater

From Malanson (1993)

floodplains and microclimate
Floodplains and Microclimate

From Malanson (1993)

changes in land cover
Changes in Land Cover

Bay Institute, 2003

CWEMF – April 2013

changes in hydrology
Changes in Hydrology

CWEMF, April 2013

changes in ecology
Changes in Ecology

CWEMF – April 2013

ecohydrology management concepts
Ecohydrology Management Concepts
  • Ecologically Significant Floods
  • Ecosystem Function Relationships
  • Seasonal Recruitment of Floodplain Vegetation
  • Survival of Floodplain Vegetation in Regulated Systems
  • Long-Term Seasonal Sustainability
ecologically significant floods
Ecologically Significant Floods
  • Large events are important geomorphically to create, disturb and maintain floodplain habitat.
  • Small/moderate longer duration events are important for species utilization.

From: McBain and Trush (XXXX)

additional design concepts
Additional Design Concepts
  • Natural levee emulation
  • Non-uniform floodplain levee storage
  • Strategic flow resistance schemes
  • Levee modifications
non uniform floodplain levee storage and levee modification concepts
Non-Uniform Floodplain Levee Storage and Levee Modification Concepts
  • Consider maintaining/modifying existing levees near river (similar to natural levees).

Uniform Floodplain Levee Storage

  • Two-stage levees increase detention storage function of floodplain.

(Jansen et al, 1979)

Non-Uniform Floodplain Levee Storage

strategic flow resistance plan view
Strategic Flow Resistance (Plan View)

Establish tree plantings in “chevron-shaped” patterns on wide floodway areas to distribute and slow the movement of overbank flood flows.

flood modeling approach
Flood Modeling Approach
  • Advantages of models in floodplain restoration design
  • Types of models
  • 1, 2 and 3 dimensional hydraulic models
  • What you need to build a model
  • Where you get the information
  • What the models show you/how to read the outputs
types of models
Types of Models
  • Hydraulic [HEC-RAS, M11, M21, M3, Delft3D]
  • Ecological [HEC-EFM, ??]
  • Biological [RIVER2D, ??]
1 2 and 3 dimensional hydraulic models
1, 2 and 3 Dimensional Hydraulic Models
  • Differences
  • Advantages/disadvantages
  • Simplification of complex systems
differences between 1 2 and 3d models
Differences Between 1, 2 and 3D Models

Source: Colorado Floodplain and Stormwater Criteria Manual (Chapter 12)

CWEMF – April 2013

differences between 1 2 and 3d models1
Differences Between 1, 2 and 3D Models

NCHRP-106, 24-24, Criteria for Selecting Hydraulic Models, December 2006

CWEMF – April 2013

differences between 1 2 and 3d models2
Differences Between 1, 2 and 3D Models

NCHRP-106, 24-24, Criteria for Selecting Hydraulic Models, December 2006

CWEMF – April 2013

differences between 1 2 and 3d models3
Differences Between 1, 2 and 3D Models

NCHRP-106, 24-24, Criteria for Selecting Hydraulic Models, December 2006

CWEMF – April 2013

take home messages
Take home messages
  • Integrating means thinking dynamically about physical and ecological process
  • Modeling is a powerful tool to help design for ecological integrity with flood safety
  • Roughness is dynamic, need to think about how it changes with conditions
  • Plants influence flow, show different roughness with different conditions, can help or hurt achieving flood management goals