Estimating the Water Requirements for Plants of Floodplain Wetlands

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Focusing on depthWater regime analysis needs to consider all components of plant waterregime. A limitation of most field investigations is their emphasis on justone, sometimes two, components, with the assumption that othercomponents have not changed. Flood frequency is often chosen,probably because it is easily quantified by inundation mapping andhydrologic modelling, but it is only one of seven components.With floodplain wetlands, the sheer size and diversity of the floodplainarea presents particular challenges. Unlike small, isolated waterbodieswhere frequency, magnitude and duration of flooding are relativelyuniform or tightly correlated, water regime is not uniform across thefloodplain; thus, statistics based on spatial averages may not bemeaningful. Ideally, flood frequency and duration, and othercomponents of plant water regime, should be estimated forhydrologically homogeneous sub-units of the floodplain wetland.However, this could result in working with numerous, very smallmanagement sub-units, making modelling an impossibility. Typically,these sub-units are aggregated and larger spatial units such as plantcommunities are considered.An alternative is to reinterpret plant water regime as spatial andtemporal variations of just one component — depth — by workingwith three states:• inundated and submerged;• inundated, but not submerged; and• not inundated.In this way, plant water regime can be modelled as a time series of thesethree states. For each state, key statistics are the mean duration and thevariability of the duration. Other useful statistics are the mean andvariability of the period between the occurrence of a given state, andthe seasonal occurrence of the three different states.Focusing on depth represents an ideal, targeted at developing models.Even if modelling is not the aim, focusing on depth is one way toreduce complexity and make it easier to work with water regime.32 Estimating the Water Requirements for Plants of Floodplain Wetlands
Section 3: A StepwiseProcedureThe process for determining the water requirements for plants offloodplain wetlands can appear complicated and even circular tothose involved in the process, but in fact it follows a series of welldefinedsteps. These steps are similar regardless of politicalprocess or which floodplain wetland is being considered. Thissection describes the five steps in this general procedure. OnlySteps 3 and 4, both purely biophysical, are treated in detail here.OutlineThe general procedure comprises five steps (Figure 11) which shouldbe followed in every investigation.Figure 11. Flow chart showing five steps for determiningthe water requirements of floodplain wetlandsplants5aRefine vegetationmanagementobjectives?ImplementationAcceptable balance?5Trade-off process with otherwater uses4Determine water regime to achievemanagement objectives3aImproverelationshipsto generatenew ones?Relationship definitions OK?3Describe relationships betweenvegetation & water regime2Set vegetation relatedmanagement objectives1Describe ecology, hydrology,uses & valuesSection 3: A Step-wise Procedure 33
Page 1 and 2: Estimating the WaterRequirements fo
Page 3 and 4: ContentsPreface 7Acknowledgments 8G
Page 5: List of Tables1 Spatial variability
Page 8 and 9: Note that the guide is concerned pr
Page 10 and 11: ecomes a matter of how to use what
Page 12 and 13: Figure 1. Floodplain featuresThe fl
Page 14 and 15: Figure 4.Wanganella Swamps, souther
Page 16 and 17: Floodplain wetlands, being a mosaic
Page 18 and 19: Section 2:Introducing theVegetation
Page 20 and 21: size and vigour rarely reach their
Page 22 and 23: floodplains survive there because t
Page 24 and 25: The lagoon floor is then colonised
Page 26 and 27: Note 11Growth-formsField guides to
Page 28 and 29: identical conditions. PFTs differ f
Page 30 and 31: Note 13Changes in depthSome herbace
Page 34 and 35: Note 15Internet dataEnvironmental d
Page 36 and 37: Step 3: Vegetation-hydrologyrelatio
Page 38 and 39: Note 19Modelling and time-stepsIn s
Page 40 and 41: Section 4: Old andNew DataOne of th
Page 42 and 43: see Figure 15), despite a three-fol
Page 44 and 45: frequency. This is rather limiting,
Page 46 and 47: Figure 13. Lippia, a floodplain wee
Page 48 and 49: single measure of the vegetation to
Page 50 and 51: Section 5:ObtainingVegetation DataW
Page 52 and 53: However, if the chosen species has
Page 54 and 55: Figure 15. Range of tree condition
Page 56 and 57: Figure 16. Spatial-temporal sequenc
Page 58 and 59: Note 26Canopy condition indexA visu
Page 60 and 61: Note 27Mapping floodplainwetland ve
Page 62 and 63: Shape of species responseThe shape
Page 64 and 65: Figure 18. Heat pulse sensorHeat pu
Page 66 and 67: section, using storage volume and i
Page 68 and 69: Figure 20. Crack volume and drying
Page 70 and 71: Figure 21. The relationshipbetween
Page 72 and 73: epresentative, there should be no m
Page 74 and 75: All of the curves are described by
Page 76 and 77: monitoring, precision levels, scali
Page 78 and 79: sites of significant recharge and d
Page 80 and 81: Figure 24. Degraded channelPart of
Page 82 and 83:
and so depth estimates are inaccura
Page 84 and 85:
Section 7:PredictingVegetationRespo
Page 86 and 87:
AEAM and the Macquarie Marshes. An
Page 88 and 89:
Category 3: hydraulic/empiricalAppr
Page 90 and 91:
For example, changes in surface and
Page 92 and 93:
ReferencesPrefaceArthington AH and
Page 94 and 95:
Section 3Roberts J and Marston F (1
Page 96 and 97:
Kunin WE and Gaston KG (1993). The
Page 98 and 99:
Singh VP (1995).“Computer models
Page 100 and 101:
Web ListingsNote 40Data on the WebM
Page 102 and 103:
flood. This has not been attempted,
Page 104 and 105:
Seven points over the flow range is
Page 106 and 107:
used as exclusions; or can be quant
Page 108 and 109:
Table A1 - 4. A flooding overlay ch
Page 110:
Table A2 - 1.(cont’d) K c and K s
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Estimating the Water Requirements for Plants of Floodplain Wetlands

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