Restoration of flow and inundation regimes

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Restoration of flow and inundation regimes

• Tom Dunne
• ESM 299 Autumn 2008

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Flow and inundation in rivers, floodplains,
lakes, estuaries

• The most fundamental characteristics of aquatic
  regime
• Also affect water-table elevations and degree of
  saturation in riparian zones
• Affect conditions for regeneration, feeding,
  growth, and refuge for plants and animals in the
  water and in the riparian zone
• Also mold the habitat through erosion and
  sedimentation, especially in river channels and
  floodplains

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Ways in which flow regimes are altered

• Flood peaks increased by altering watershed
  conditions or reduced by impoundment
• Flows decreased by water diversion or consumptive
  use (evaporation)
• Seasonal timing altered by impoundment and
  releases for food and energy production or flood
  relief
• Annual amplitude reduced at both ends of flow
  scale
• Water temperatures altered by impoundment and
  altered seasonality
• Severing of connections between channel and
  floodplain or other wetlands (altering
  hydroperiod)

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Common needs for flow restoration
Generalization

• Favorable instream flow conditions for animals
• Improve inundation regimes of refuge water bodies
  (e.g. flooded areas for migratory waterfowl at
  critical seasons widespread wildlife refuges in
  Central Valley)
• Re-establish preferred channel and floodplain
  conditions and processes for ecology, recreation,
  esthetics
• Reduce flood risk

Karr (1991)
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Examples of the role of flow magnitude and
frequency in defining habitat A Water tables
sustain riparian vegetation and delineate
in-channel baseflow habitat
A
Poff et al., Bioscience (1997)
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Examples of the role of flow magnitude and
frequency in defining habitat B Small,
frequent floods transport fine, organic sediments
(food) and maintain spawning substrates for
fishes
B
B
Poff et al. (1997)
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Examples of the role of flow magnitude and
frequency in defining habitat C
Intermediate-sized floods transport and clean bed
material, scale the size and shape of most
channels, and inundate lower parts of floodplains
C
C
Poff et al. (1997)
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Examples of the role of flow magnitude and
frequency in defining habitat D
Intermediate-sized floods inundate floodplains,
depositing fine sediment and seeds for pioneer
plants
D
D
Poff et al. (1997)
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Examples of the role of flow magnitude and
frequency in defining habitat E Rare, large
floods uproot mature trees from banks and topple
them into channels as LWD jams, scour new
channels across floodplains, break up dense
floodplain tree covers and spread seeds creating
diverse vegetation communities.
E
E
Poff et al. (1997)
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Watershed scales at which flow restoration
problems arise (often flow not the only problem)

• Post-fire flooding in small watersheds Los
  Alamos, Goleta
• Urban effects and hydromodification in small
  watersheds
• Flooding in small watersheds devastated by
  agricultural soil erosion
• Etc., etc.

• Missouri R spawning conditions off-channel
  rearing.
• Colorado R. flood reduction reduces sand bars
  and allows buildup of dangerous rapids
• Dams, reservoirs, and flow diversions
• San Joaquin
• Sacramento pumping and delta smelt
• Tributaries flow releases to flush smolts out
  of river before they die of heat stress

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Hydromulching to restore infiltration capacity
and reduce erodibility
SB Independent
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Watershed scales at which flow restoration
problems arise (often flow not the only problem)

• Post-fire flooding in small watersheds Los
  Alamos, Goleta
• Urban effects and hydromodification in small
  watersheds
• Flooding in small watersheds devastated by
  agricultural soil erosion
• Etc., etc.

• Missouri R spawning conditions off-channel
  rearing.
• Colorado R. flood reduction reduces sand bars
  and allows buildup of dangerous rapids
• Dams, reservoirs, and flow diversions
• San Joaquin
• Sacramento pumping and delta smelt
• Tributaries flow releases to flush smolts out
  of river before they die of heat stress

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Tuolumne R. regulated streamflow
(Tuolumne R. Technical Advisory Committee, 2000)
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Flood-frequency curves for Merced R. before and
after impoundment (Tuolumne R. Technical Advisory
Committee, 2000)
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R. Euphrates hydrograph
Partow 2001
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Mesopotamian Marshlands(Partow, UNEP, 2001)
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Characteristics of water regime important for
ecosystem functions in rivers, lakes, estuaries

• Duration and season of inundation (hydroperiod)
• Depends on climate and drainage area of basin
• Altered by reservoir storage or flow diversion
• Reliability of inundation
• Some species require secure flow regimes others
  opportunistic
• Connectivity
• Dam construction or dewatering of reaches
  interrupts passage of organisms, reduces usable
  area, or confines a species that was formerly an
  upstream, cold-water species to a lowland species
  in warmer water (e.g salmon in Sacramento River
  tributaries)
• Channel-floodplain connection increases diversity
  and range of habitat conditions and food
• Flow depth and velocity
• Depend on discharge, gradient, and channel
  resistance Mannings equation
• All driven by the discharge regimes, which are
  complex

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Seasonal and inter-annual discharge regimes
Upper Colorado, snowmelt and late summer rains
Mississippi, rain-fed summer maximum Poff and
Ward (1990)
Difficult to describe in any simple general way
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One response could be to pick a single
reasonable metric of flow regime alteration
thought to be related to some habitat
changeExample of channel change resulting from
flow regulation, Duchesne R, Utah
Gaeuman et al, Geomorphology (2005)
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Another could be to develop more complex metrics,
e.g. Indicators of Hydrologic AlterationIHA
method
Galat and Lipkin, Hydrobiologia, 2000 Richter et
al, Conservation Biology, 1996
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Degree of hydrologic alteration along Missouri R.
Galat and Lipkin, Hydrobiologia, 2000
Read methodology
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Purposes for altering flow regimes (1)

• Flood control either to reduce inundation hazard
  or to keep flow from eroding channel or levees.
• Requires flood routing (HEC-RAS)
• Flushing fine sediment out of impacted gravel
  spawning areas (flushing flows). Usually
  empirically established thresholds using after
  initial calculation of bed mobility (Shields).
• scour chains
• MacNeil samplers (15 cm diameter pipes hammered
  into bed and sediment excavated for sieving)
• freeze-coring for fine sediment characterization
  
• Reduce water temperatures (occasionally raise
  them by avoiding release of cold, deep water from
  reservoirs).
• Requires water temperature modeling or
  empirically established relations

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Purposes for altering flow regimes (2)

• Alter extent and/or connectedness of habitat
  depth and velocity.
• Modeling of instream flows for characterizing
  habitat quality
• Life-history models for a species
• Restoring channel mobility, floodplain
  disturbance, and connection of channel flow and
  floodplain water bodies (geomorphic flows)
• Chronosequences of maps, aerial photos,
  cross-section surveys
• Modeling of probable channel change for an
  expected flow regime

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Methods for restoring flows

• Remove dams or diversions and breach artificial
  levees
• (CA Bay-Delta, Lower Danube, Elwah R., WA. And
  other dam removal projects)
• Release more water, but very expensive
• (Calfed 800,000 acre-feet/yr of environmental
  water). Requires extensive negotiation and
  justification through habitat-flow simulation.
• Purchase smaller amounts of water for targeted
  releases on an opportunistic basis,
• e.g. for planned floods (Colorado R.) or for
  emergency relief of fish or water quality or
  temperature constraints (Trinity R.).

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Water releases

• Political agreements
• Users ordered or agree to forgo a certain
  proportion of their water rights in order to
  retain the rest (w/wo recompense)
• Economic agreements
• Willing sellers agree on a year or multi-year
  basis to sell their water to an agency so that it
  can be released at a time and place that is
  favorable to ecological processes. E.g..
• Water Acquisition Program of Central Valley
  Project of BuRec and USFWS
• Environmental Water Account of CalFed
• Purchase water (15-700/acre-foot depending on
  year and season) and release to improve access to
  spawning, lower temperatures for spawning, flush
  smolts from tributaries, passage of fish thru
  delta (www.usbr.gov/mp/cvpia/wap).
• come from water and power users and State
  bonds

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Methods for restoring flows

• Remove dams or diversions and breach artificial
  levees
• (CA Bay-Delta, Lower Danube, Elwah R., WA. And
  other dam removal projects)
• Release more water, but very expensive
• (Calfed 800,000 acre-feet/yr of environmental
  water). Requires extensive negotiation and
  justification through habitat-flow simulation.
• Purchase smaller amounts of water for targeted
  releases on an opportunistic basis,
• e.g. for planned floods (Colorado R.) or for
  emergency relief of fish or water quality or
  temperature constraints (Trinity R.).
• Re-scale river channel to smaller flows
• increase mobility of channel bed and banks,
  increase frequency of overbank flow.

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Operationalizing flow restoration design to
produce benefits (e.g. of habitat) after deciding
why you want to restore/alter flows Design phase
for cost-benefit analysis Factors that control
the distribution of a given discharge of water in
a channel-floodplain system

• Discharge
• Cross sectional geometry of lowest flow path
• Gradient of flow path (channel)
• Hydraulic resistance to flow (bed texture,
  vegetation, woody debris)

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Operationalizing flow restoration design to
produce benefits (e.g. of habitat) after deciding
why you want to restore/alter flows Design phase
for cost-benefit analysis

• PHABSIM model one-dimensional flow assumed
• RIVER2D model two-dimensional flow allowed
• Both require large inputs of topographic survey
  data and therefore of labor
• Both predict distribution of flow depth and
  velocity and require measurement of substrate
  texture.
• Output compared to tables of habitat preferences
  for various species to produce maps of the
  distribution and amount of various forms of
  habitat (e.g. chinook spawning habitat
  juvenile steelhead rearing habitat)

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Map of stream cells from PHABSIM
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
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Effective habitat concept in PHABSIM
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
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PHABSIM translation of structural and hydraulic
characteristics into an area of suitable
microhabitat for a target species
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
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Flow-habitat simulationInstream Flow Incremental
Methodology IFIM
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Relation between weighted usable area and
standing crop of cutthroat trout, Yellowstone NP
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
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Steady uniform flow downstream in a
channel-floodplain system
Floodplain A
Floodplain B
Channel
Q is the sum of three channels coupled by a
horizontal water surface
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Floodplain habitats(Tuolumne R. Technical
Advisory Committee, 2000)
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Digital Elevation Data (1990s)
1 meter contour elevation map
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www.fort.usgs.gov/products/Publications/3910/3910.
pdf
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Full habitat-flow simulation requires

• Combination of hydraulic modeling with
  hydroperiod
• Consideration of geomorphology of stream channels
  and floodplains --- can they be re-engineered to
  provide improved conditions?
• Negotiation of regulated flows

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Public safety

• Dont forget that flood hazard regulation is
  likely to trump ecological flow needs in most
  restoration projects near developed areas.
• In dam removal projects in remote areas there is
  a better chance of negotiating the flexibility to
  allow flows that will disturb channels and
  floodplains
• See Watershed Analysis or River Restoration
  courses for flood hydraulics modeling exercises

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Readings on Flow Restoration

• Poff, N. L. et al. The natural flow regime.
  Bioscience, 47, p. 769784, 1997.
• Junk, W.J. The flood pulse concept new aspects,
  approaches, and applications an update, undated
  ms.
• Gaeuman, D. et al., Complex channel responses to
  changes in stream flow and sediment supply on the
  lower Duchesne River, Utah, Geomorphology, 64,
  185206, 2005