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Restoration of flow and inundation regimes

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Title: Restoration of flow and inundation regimes


1
Restoration of flow and inundation regimes
  • Tom Dunne
  • ESM 299 Autumn 2008

2
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

3
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)

4
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)
5
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)
6
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)
7
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)
8
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)
9
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)
10
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

11
Hydromulching to restore infiltration capacity
and reduce erodibility
SB Independent
12
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

13
Tuolumne R. regulated streamflow
(Tuolumne R. Technical Advisory Committee, 2000)
14
Flood-frequency curves for Merced R. before and
after impoundment (Tuolumne R. Technical Advisory
Committee, 2000)
15
R. Euphrates hydrograph
Partow 2001
16
Mesopotamian Marshlands(Partow, UNEP, 2001)
17
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

18
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
19
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)
20
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
21
Degree of hydrologic alteration along Missouri R.
Galat and Lipkin, Hydrobiologia, 2000
Read methodology
22
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

23
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

24
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.).

25
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

26
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.

27
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)

28
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)

29
Map of stream cells from PHABSIM
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
30
Effective habitat concept in PHABSIM
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
31
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
32
Flow-habitat simulationInstream Flow Incremental
Methodology IFIM
33
Relation between weighted usable area and
standing crop of cutthroat trout, Yellowstone NP
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
34
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
35
Floodplain habitats(Tuolumne R. Technical
Advisory Committee, 2000)
36
Digital Elevation Data (1990s)
1 meter contour elevation map
37
www.fort.usgs.gov/products/Publications/3910/3910.
pdf
38
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

39
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

40
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
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