Estimating the Water Requirements for Plants of Floodplain Wetlands

Table A2 – 1.(cont’d) K c and K s for plant communitiestypical of south-eastern AustraliaPlant community(Structure + Dominant)AQUATIC HERB-dominated plant communities —cont’dSubmerged plants – with either blade or dissectedleaveseg. ribbon weed (Vallisneria) and sago weed(Potamogeton)Free floating vegetation• Small forms (LAI approx 1.0 and flat on surface) mainlyAzolla and duckweeds• Larger forms (LAI 2.0+ and over 25 cm high) unusual intemperate Australia, eg. outbreak of water hyacinthlimited to GwydirLINEAR features & PATCHESOpen water – in channels flanked by wet swamp 1.2vegetationChannels with tall riparian woodland 1.4–1.5Channels with open water patches and emergent 1.3grass-like macrophytesPaleostreams or dry channels which are vegetated by 0.4–0.6treesBare areas, salt encrusted areas of low infiltration and 0.05, rarely 0.2low water storage capacityK c1.15 Not applicable1.2 Not applicableK sEstimates of K c and K s values are expected to be applicable to differentplant communities on floodplain wetlands. Plant communities aredescribed by structural attributes, and assume large areas unlessotherwise stated, for example linear strips of woodland. Theseestimates are based on experience in evapotranspiration estimates,work done on different plant communities in the Okavango Delta,Botswana, and Australia, where relevant data are applicable. Publishedvalues in scientific literature are generally not available for Australianfloodplain communities (P.M. Fleming, pers. comm. 1999). When usingpublished evapotranspiration data for wetland plants, not only is itnecessary to be aware of whether evapotranspiration was measureddirectly or indirectly (Section 6) but to know what ‘reference’ value wasused as these differ. The magnitude of differences in reference values isbest appreciated by relating them (Table A2 – 2) to the standardreference surface recommended here, the well-watered grass surface(Section 6).Table A2 – 2. Range of reference values, relative to wellwateredgrassStandard grass surface 1.0Open shallow water 1.2Alfalfa or lucerne surface 1.3Standard US Class A pan evaporimeter 1.4–1.5US Class A pan with bird screen 1.3–1.4Australian sunken tank 1.2110 Estimating the Water Requirements for Plants of Floodplain Wetlands