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METHODS FOR ASSESSING ENVIRONMENTAL FLOWS

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METHODS FOR ASSESSING ENVIRONMENTAL FLOWS Powered By Docstoc
					METHODS FOR ASSESSING
ENVIRONMENTAL FLOWS


  Curso de Caudales Ambientales
       ,                  ,
  Lima, Peru. Nov 25 to 27, 2009


                O Keeffe,
            Jay O’Keeffe
WWF Professor of Freshwater Ecosystems,
Department of Environmental Resources
          Tennant
      HYDRAULICS
      Velocity, Depth,
   Hughes Extrapolation
         Substrate
           IHA



HYDROLOGY
Flows in m3/sec




The Engineer      The Ecologist   2
        HYDRAULICS
        Velocity, Depth
        Velocity Depth,
       Substrate, Wetted
           Perimeter

                             ECOLOGY
                              Habitat types
                           Ecological processes
HYDROLOGY                   Indicator species
Flows in m3/sec




The Engineer         The Ecologist                3
4
                                                 Maintenance Flow BBM 3 Mara River

                                45
                                                                       Present Day
                                                                                   (BF
                                                                       Recommended (BF+ Floods)
      onthly flo (cub. m/sec)



                                40                                     Recommended Base Flow (BF)
                                35
                     .




                                30
                                25
               ow




                                20
                                15
Ave. Mo




                                10
                                5
                                0
                                     Jan   Feb Mar   Apr   May   Jun   Jul   Aug Sep Oct   Nov Dec
                                                                  Month
                                                                                                 5
                                                        Drought Flow BBM 3 Mara River

                                25                                          Present Day
                                                                            Recommended (BF+ Floods)
                                                                            Recommended Base Flow (BF)
Ave. Monthly flow (cub m/sec)




                                20
                     b.




                                15
             f




                                10
     M




                                 5


                                 0
                                     Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec
                                                                    Month


                                                                                                             6
    GENERIC TYPES OF
ASSESSMENT METHODOLOGY


•   Hydrology-based/Look-up table approaches
•   Extrapolation approach
•    y             g          g
    Hydraulic rating methodologies
•   Habitat simulation methodologies
•   Holistic   th d l i
    H li ti methodologies


                                               7
HYDROLOGY-BASED/LOOK-
 UP TABLE APPROACHES
• Range of Variability Approach (Richter et al,
  1997)
  – 32 hydrological statistics (Mean annual max and
           da      day max           etc.)
    min; 7 day, 30 da ma and min etc )
  – Range of acceptable variation defined
  – Aim: to maintain essential variability


                 (Tennant,
• Montana Method (Tennant 1976)


                                                      8
Wet Season   Dry Season




                          9
          The Indicators of Hydrologic Alteration (IHA)
A software program developed by The US Nature Conservancy, examines
                                                                      data.
over 67ecologically relevant statistics derived from daily hydrologic data




                                                                     10
ADVANTAGES AND DISADVANTAGES
    (HYDROLOGY-BASED/LOOK-UP
    (HYDROLOGY BASED/LOOK UP TABLE APPROACHES)

•   I        i      d    id i h i l d           i
    Inexpensive and rapid, with simple data requirements
•   Potential for regionalisation
•   Suitable for reconnaissance level assessments
•   Can be upgraded by professional j g
             pg        yp                                  p
                                      judgement or local input
But:
• Absence of ecological support
• Low confidence answers, difficult to defend
• Danger of extrapolation to unsuitable different regions


                                                         11
EXTRAPOLATION APPROACH
  Hughes d Munster
• H h and M t (2000)
 – Correlation of previous detailed assessments
 – Rivers typed by regional and site-specific flow
   characteristics
 – and by generic ecological objectives: A (natural,
   unmodified) to D (Largely modified)




                                                12
                                        Flow requirements for ecological categories A to D
                                                (after H h      d Munster, 2000)
                                                ( ft Hughes and M       t


                                        2
                                        75 5
Annual T otal Re quire me nt (% M AR)




                                        2
                                        60 0
                        e




                                        45 5
                                        1




                                                                                                A
               e




                                        30 0
                                         1


                                                                                                B
                                                                                                    C
                                        15 5


                                                                                                    D
                                          0
                                               0   5      10           15            20    25                30
                                                          H y d r o lo g ic a l In d e x                13
ADVANTAGES AND DISADVANTAGES
                (Extrapolation approach)
                (E t    l ti          h)



 • Incorporates previous expertise and experience
 • Very inexpensive and simple to apply
 • Suitable for assessments at the reconnaissance level
 But:
 • Requires extensive previous detailed assessments to
   develop
 • Assumptions of ecological homogeneity
 • Low to medium confidence, difficult to defend.

                                                      14
      HYDRAULIC RATING
       METHODOLOGIES


• eg Review by Gippel and Stewardson (1996)
  – Rated river x-sections
                  g g y          (depth,
  – Measure changing hydraulics ( p velocity,  y
    wetted perimeter), with changing discharge




                                                   15
                            IFR 2 : SKIETDRIFT - 1.48 m3/S




                 2

                1.8

                1.6

                1.4
Elevation (m)




                1.2
          (




                 1

                0.8

                0.6

                0.4

                0.2

                 0
                      10   20   30           40     50   60   70
                                     Chainage (m)


                                                                   16
ADVANTAGES AND DISADVANTAGES
       (HYDRAULIC RATING METHODOLOGIES)



•   Can incorporate ecological habitat information
•   R l i l inexpensive and simple to apply
    Relatively i        i     d i l          l
•   Flexible according to available data
•   Suitable for assessments at the reconnaissance/medium
    level
But:
• Simplistic assumptions extrapolating from single
  cross-sections
• Low to medium confidence difficult to defend
                  confidence,             defend.
                                                      17
   HABITAT SIMULATION
    METHODOLOGIES
       (Milh        l
• IFIM (Milhous et al, 1989)
  –   Model habitat changes with changing flow
  –   Use multiple X-sections
  –   Link to habitat preferences for selected biota
  –   Identify flows at which optimum habitat is
      available




                                                   18
19
                             3
IFR 14 : Lower Buffalo 0.68 m /S




                                   20
21
22
ADVANTAGES AND DISADVANTAGES
        (        S U     ON     O O OG S)
        (HABITAT SIMULATION METHODOLOGIES)

•   High resolution characterisation of habitat availability
•   Flexible for the assessment of different flow scenarios
•               use,
    In frequent use high degree of scientific acceptability
•   Legally defensible in the USA
But:
B t
•   Largely confined to target species
•   Resource and time intensive
•   Limited transferability between rivers
                          y
•   Complexity of computer programming
•   Low resolution of other aspects
                                                           23
HOLISTIC METHODOLOGIES
   Building Bl k M th d l   (King d
 • B ildi Block Methodology (Ki and
   Louw, 1998)
   – Use multi-disciplinary expert panel
   – Relate habitat availability for a range of
     indicators to different flows
   – Reach consensus on flows required for prepre-
     defined objectives



                                                     24
25
ADVANTAGES AND DISADVANTAGES
              ( O S C       O O OG S)
              (HOLISTIC METHODOLOGIES)

•   Ecosystem (rather than limited species) assessement
•   Multi-disciplinary consideration of riverine processes
•   Flexible in response to data availability
•   High confidence answers (because of specialist concensus)
•   Potential f      i li ti
    P t ti l for regionalisation
But:
• High resource requirements
• Subjectivity may result in variable results from different
  S j         y y
  specialists

                                                         26
SOME RECENT DEVELOPMENTS
 • DRIFT – D        t
             Downstream R             to Imposed
                             Response t I      d
   Flow Transformations (Brown and King,
   2000)
                                     (O Keeffe
 • FS/R – Flow Stressor Response (O’Keeffe et
   al, 2002)
 • ELOHA – Ecological Limits of Hydrologic
              (                    )
   Alteration (Poff et al, in Press)


                                             27
                   DRIFT
  Holistic t d           th d l
• H li ti top-down methodology
• Predicts the effects of successive flow reductions on
  a range of indicators
• Develops a database of thousands of individual
  consequences and their severity
• Social and economic costs and benefits are also
  assessed




                                                  28
    ADVANTAGES AND DISADVANTAGES
                             (     )
                             (DRIFT)

•      Top down
       Top-down approach is precautionary
•      Database facility allows assessment of a wide range
       of flow scenarios
•      Provides an audit trail for decisions
•      Can be used with a wide range of data availability
•      Potential for regionalisation
But:
B t
•      Initially resource intensive
•      Database lists indiv. impacts, but lacks integration facility
•         p          pp         y
       Top-down approach may be less defensible
                                                             29
FLOW STRESSOR/RESPONSE

• Standardised index of increasing stress as flows reduce
                                            abundance
• Responses characterised as changing abundance,
  increasing risk to critical life stages, and finally
  extinction
• Stress levels related to site-specific flows
                                       series,
• Hydrologist provides stress time series duration curves
  and spell analyses for any flow scenario
• Specialists assess consequences of each scenario


                                                      30
    ADVANTAGES AND DISADVANTAGES
                ( OW S    SSO / S ONS )
                (FLOW STRESSOR/RESPONSE)
•      Integrates the ecological risks of flow reductions
•                  magnitude
       Addresses magnitude, frequency and duration of effects
•      Allows for gradual changes, not assumed thresholds
•      1 ti capture of k
       1-time     t             l d        li d to ll flow   i
                        f knowledge applied t all fl scenarios
•      Encourages consistent application of expert judgement
•      Provides an audit trail for decisions
•      Can be used with a wide range of data availability
•      Potential for regionalisation
But:
•      Initially resource intensive
•      Only deals with low flows at present
                                                        31
                g
  ELOHA – Ecological Limits of
    Hydrological Alteration
      (In development)
      (I d l          t)
  Regional/global      l
• R i l/ l b l scale assessments
    y      g                         p
• Hydrologic models for undeveloped and
  developed rivers regionally
• Classification system: to delineate types of
  rivers/parts of rivers that can be treated as
  similar for EWA
• Regional flow-ecology response curves

                                                  32
THE USE OF MULTIPLE LEVELS
      OF ASSESSMENT
 • The South African policy: Increasing levels
   of detail, and confidence, using increasing
   resources
   An l        i          h Mi i         h d
 • A alternative approach: Mixing methods to
   get the maximum advantages




                                             33
 SOUTH AFRICAN POLICY
                    Low confidence,
• Desktop model: Lo confidence half a day da
• Rapid: Desktop model, plus limited
  verification, low/medium confidence, 2 to 4
  weeks
• Intermediate: Scaled down holistic methods,
  limited hydraulics, medium confidence, 60 days
• Comprehensive: Full holistic method, high
  confidence,
  confidence 8 months to 2 years


                                            34
     Ecological Reserve procedures
  Reference            Classification and
  conditions               objectives
                      DRIFT
 Present
Ecological
      i               DRIFT
  State              Database


 Ecological
       g            Flow Stressor
Importance          R
                    Response
    and
                             PHABSIM
 Sensitivity
 S ii i
       SOME CONCLUSIONS
•   Gradual changes and thresholds
•   Science and values
•   T i and verification
    Testing d       ifi i
•   Long-term effects of flow regulation
•   Non-flow related problems
•   Costs and benefits of environmental flows
•   Implementation
•   Social aspects of environmental flows, and stakeholder
    involvement

                                                     36

				
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