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Title: Determining The Freshwater Flow Needs Of Estuaries
Author: Bartlett JM
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_527, Representation ID: 186, Object ID: 1865
Scope of study The overall-aim of this study is to establish best practice, shortcomings and future research needs in determining freshwater flow needs of estuaries. In particular, the study.examines the use of computational, including statistical, modelling. The study has reviewed: . . . existing relevant R and D; estuarine processes and uses; andthe present and.possible future use of computational modelling techniques for estuarine analysis, especially in determining the minimums flow needs of estuaries. It gives guidance,on: . . . a methodology!for.the determination of minimum flow needs; the general and data collection requirements of various types of models; and carrying- out a preliminary assessment before starting a major study., The outputs from the study are: . . . This R and D Technical Report (W113) that identifies shortcomings, best -practice, implementation benefits and future R and D of freshwater flow needs to estuaries; and A quality control-manual (R and D Technical-Report W168) to be used when undertaking a computational model study. R and D Technical Summary WS107:. Relevant:R and D Relatively little -R and D:has been directed towards the freshwater flow needs of estuaries and the determinatiorrof residual flows. There is, however existing or ongoing research into: . . . . . Aspects, of computational modelling, providing support to residual flow determination; Residual flows in rivers, The Surface Water Abstraction-Licensing Policy (SWALP) procedure is designed to consistently assessapplications for surface water abstractions. Morphology., Current MAFF looking at methods-for the prediction of long term morphological change caused by changes in the estuary. Fisheries research.: This includes research into minimum acceptable flows and-the effect of temperature on Risk assessment. Research into risk assessmentmethods in management decision making and long term.corporate planning.. A risk assessment,approach. has been used in the determination of freshwater flow needs in this study. R and D Technical Report W 1.13 iv Estuarine processes and uses Most short term estuarine processes are well understood and can be simulated by computational models or other analytical methods. However, there are major gaps in knowledge in: . . . Long term morphological change; The relationship of sediment and ecology; and Ecological mechanisms. Present and future use of modelling techniques Computational modelling is closely linked to the computing power available. It is certain that the power available on the average modelleras desk at low cost will continue to escalate. It will become possible to create models that are: . . . . more realistic, using more complex algorithms to simulate hydrodynamic, chemical or ecological functions; more detailed in space and longer in time; more integrated, with a single model being used for a range of functions; and simulates morphology and ecology with confidence. Modelling is widely used in the Agency for flow and quality analyses. However, less advance has been made in the use of models to determine the freshwater flow needs of estuaries. Methodology for determining freshwater flow needs This report sets out a management and technical approach to freshwater flow need studies. The approach is designed to make best use of existing and emerging technology. The approach also allows the manager to use simple methods of analysis where budget dictates, although it should be stressed that the use of such simple methods should be seen as less than ideal, adding little to oneas knowledge of the management or needs of an estuary than the methods used to fix the last round of Minimum Residual Flows (MRFs) a generation ago. The management approach stressesthe need for a coherent data management policy. At present data collected by the Agency may not always be easily retrievable for future studies. A policy is needed that: . . . . Encourages project teams to archive data; Creates a simple, yet comprehensive, database to allow retrieval of this data; Makes use of the best technology, such as geographical information systems (GIS); and Collects long term morphological data in advance of computational modelling developments in this field. R and D Technical Report W 113 V A technical approach for the determination of freshwater flow needs is proposed, using concepts from.risk assessment, This approach-isshown below: Review existing reports and check data availability. Classify estuary-type and select estuary reaches. ISTAGE 1 Determine external review, complete data and impact matrices. For low impact uses and processes, use simple analysis methods. If appropriate, carry out preliminary analysis. Review design standards and set out study standards. Complete risk matrix, seasonal variations and risk assessment. For each use and reach, select appropriate analysis method. Rationalise and optimise model design. Cost modelling studies. Consider joint funding of modelling, or simpler models. Set up modelling contracts.. Carry out or manage modelling studies. Analyse model results and set MRF. i: Post-project appraisal. R and D Technical Report. W 113 I. vi .:, Recommendations This report recommends the following future R and D needs: . The technical approach described should: a> W . be trialed; and its application to disciplines other than water resources considered. Each region should develop a strategic computational modelling plan that: indicates the management approach for each estuary, as to whether modelling will be carried out in-house, jointly, or by audit only; proposes a strategic programme for in-house modelling; and . Data collection and management should be reviewed, then: 4 b) 4 4 a fi11ly integrated and focused data monitoring strategy adopted; a consistent policy on data adopted between regions; a minimum specification database to archive estuarine data developed; and a GIS should be used for this data archive. . An overview should be kept of advances in morphological techniques to identify any future R and D needs. . Data collected by the Agency does not include data sufficient for the building of morphological models to predict long term changes in an estuary. The Agency should: a> b) . and estuarine modelling keep the ongoing MAFF sponsored research on morphology in view; and implement a morphological data collection programme as soon as is practicable. Agency functional groups and policy makers should consider whether: a) b) 4 the Agencyas computational modelling budgets are adequate for the Agency to maintain its capability in computational modelling: the Agencyas regulatory role if carried out through review and audit of others work alone, if modelling is no longer carried out; and whether the Agency loses its independence as a regulator if it co-operates with other interested parties in developing estuary models. R and D Technical Report W 113 vii Part A -
Publisher: Environment Agency
Subject Keywords: River; Modelling; Flow; Estuaries
Extent: 194
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