Ecosystem Management Efforts Should Be Considered Experiments, Testing The

Ecosystem management efforts should be considered experiments, testing the need to maintain or restore natural hydrologic regime characteristics in order to sustain ecosystem integrity. Only some limited studies have closely examined hydrologic influences on ecosystem integrity and this is mainly because most of the commonly used statistical tools are poorly suited for characterizing hydrologic data into biologically relevant attributes (BD, Richter, etal, 1997). Without such knowledge, ecosystem managers will not be compelled to protect or restore natural hydrologic regime characteristics. However, recently, there have been some significant developments in the field of hydrological studies and importantly few robust computer statistical tools and models like IHA & Range of Variability Approach (RVA) using the (Indicators of Hydrologic Alterations, BD, Richter, etal, 1997), Wetted Physical Habitat Simulation System (PHABSIM Model, Jowett, 1997)35, Flow Incremental Methodology (FIM), other Hydrologic Modelling Software like GAWSER, Ontario Flow Assessment Techniques (OFAT), etc. are now know to exist (Jowett, 1997).
The following sections attempt to evaluate and assess the possible effects of hydrological alteration specifically induced by human interventions or activities. A very useful computer model called the IHA model (available at Freshwaters.com) has been used for generating and evaluating the effects of flow variations. The ecological zone considered for analysis in this paper is the 'Exe river Estuary' region and the gauging station selected is 45001 - Exe at Thorverton.
The Indicators of Hydrologic Alteration (IHA) Method Approaches & Application
The evaluation and assessment of the flow regime of the Exe-river system and the variations it witnessed after the construction of the 'Wimbleball Reservoir' have been accomplished by the application of a very detailed computer-modeling tool known as the IHA or 'Indicators of Hydrologic Assessment' model. The software basically takes birth from the concept of integrity and wholesomeness of the 'natural flow regime' and is configured and capable of determining the relative transformations and variations in this natural flow regime subject to any natural or artificial modifications or alterations (BD, Richter, etal, 1997). At first, it requires defining and identifying a series of biologically-relevant hydrologic attributes that characterize intra and inter-annual variations in water conditions which are further processed for a robust statistical variation analysis after isolating the data-sets to represent two different periods resembling the pre-impact and post-impact scenarios (Rosenberg, et al, 2002).