Estimating the Water Requirements for Plants of Floodplain Wetlands

and so depth estimates are inaccurate and the storage volume decayfunction is not seasonally variable. This means that the strongly seasonalpatterns in evapotranspiration cannot be represented.The lower River Murray, South AustraliaFor the floodplain of the lower River Murray in South Australia, aninundation prediction model has been developed based on satelliteimagery.The model predicts the area of the floodplain inundated solely on thebasis of river flow level. River and weir–pool water levels are simulatedusing the River Murray Flow Model. Satellite images taken at knownriver levels were used to develop a relationship between area inundatedand river water levels.The floodplain is represented as a series of ‘flood inundation responseunits’ each of which floods in response to a given water level at a given‘trigger point’ (Sykora 1999). The model predicts whether an area of thefloodplain will be wet or dry at any given time, but does not predictwater depth. Because there are several locks to regulate water levels onthe lower river, there is a considerable degree of control over whatareas will be flooded. Furthermore, the low river gradients mean theflood hydrograph travels slowly, and so with advance warning, lockscan be manipulated either to minimise flooding (opening locks), or toinundate certain areas for environmental purposes.The Macintyre and RUBICONThe model developed for the lower Macintyre River floodplain used theRUBICON unsteady flow hydraulic model. The RUBICON model wasdeveloped by the Wallingford Institute of Hydrology (UK) and theDanish Hydraulics Institute. It was applied to the Macintyre Riverfloodplain to investigate the impacts of proposed levee constructions,but could also be used for environmental investigations. RUBICONrepresents floodplains as a network of nodes and linking branches.Hydraulic model for the Condamine–BalonneFor the Condamine–Balonne River floodplain, SMEC used an ‘in-house’hydraulic model which employs an implicit finite difference algorithmto solve the equations for conservation of water mass and momentumand thus route flows through a multi-channel network. Importantly,even during the rising limb of the flood hydrograph, the direct rainfallinputs to the water surface and the evaporation and infiltration losseswere large, and had to be computed at every time step (Marr 1999).IQQM in New South WalesThe Integrated Quantity and Quality Model (IQQM) of river hydrologydeveloped by the New South Wales Department of Land and WaterConservation has used several different representations of floodplainsand wetlands (Podger, pers. comm. 1999).• In the model of the Border Rivers system, several floodplainstorages are linked to the river channel. Variable flows into thesestorages are calculated as a function of the water level differencebetween the river and the storage, and of the crest level betweenthe river and the storage. Flows back from the storage to the riveroccur at a constant rate below a given level difference threshold.82 Estimating the Water Requirements for Plants of Floodplain Wetlands