Prognosebaseret vandindvinding og modeller for vandløbspåvirkning

Abstract

I dag gives indvindingstilladelser til bl.a. den almene vandforsyning som en tilladelse til indvinding af en fast årlig vandmængde. Størrelsen af tilladelsen er, grundet de naturlige variationer i ressourcens størrelse, i nogle tilfælde konservativ, og den bæredygtige tilgængelige ressource er større, end hvad der indvindes. I dette projekt undersøges en indvindingsstrategi, hvor der både tages hensyn til de naturlige variationer i grundvandsressourcens størrelse og muligheden for maksimal udnyttelse af ressourcen. Det undersøgte koncept tager udgangspunkt i udvikling af modeller til fremskrivning af årsminimumvandføringen og undersøgelse af en simpel habitatmodel til vurdering af habitatkvantiteten i vandløb. Der er brugt to metoder til fremskrivning af årsminimumvandføringen: Lineære regressionsmodeller og trænede neurale netværksmodeller. Begge metoder tager udgangspunkt i pejledata som inputdata. På baggrund af størrelsen af årsminimumvandføringen bestemmes det tilgængelige habitatareal med habitatmodellering. Ud fra dette kan den kommende sæsons indvindingsstrategi tilrettelægges. I dette projekt er ovenstående undersøgt gennem et case-studie af Binderup Å. Hertil er der med lineær regression udført en model til fremskrivning af årsminimumvandføringen med 95% sikkerhedsinterval på 95 l/s og en model trænet med neurale netværk med et 95% sikkerhedsinterval på 61 l/s. Ydermere er der udført en simpel habitatmodel med tværsnit fra DK-modellen, hvis resultater kun afviger minimalt fra en habitatmodel med tværsnit opmålt i forbindelse med dette projekt. Konceptet med den simple habitatmodel er benyttet til at lave habitatmodeller for hele Binderup Å for yngel, juvenil og voksen ørred, så habitatkvantiteten kan vurderes ved forskellige vandføringer

Today Danish groundwater abstraction licenses are given as a license to abstract a certain amount of groundwater every year over a period of years. Due to the natural variations in the size of the groundwater reservoir, this is a rather conservative approach to giving groundwater abstraction licenses, as the availability of the sustainable resource is sometimes higher than what is being abstracted. Thus, it is the aim for this project to investigate a strategy for groundwater abstraction in which it is possible to abstract a maximum amount of groundwater whilst taking the natural variations in the available resource into account. Furthermore, the possibility to perform habitat modelling with simpler habitat models is investigated. The investigation of this strategy commences with a study of the possibility to develop models for prediction of the yearly minimum flow in streams and assessing the equivalent habitat area with habitat modelling. Two methods for prediction of the yearly minimum flow in streams are investigated: Linear models and trained neural network models. Both prediction model concepts use measurements of groundwater level from late winter or early spring as input data. Based on the prediction of the minimum flow, the goal is to assess the corresponding habitat area in order to evaluate the possibility to abstract more or less the following year. In this project, the above mentioned is investigated through a case study of Binderup Å situated in North Jutland, Denmark. For this purpose, the two model concepts, linear modelling and neural network models, have been used to produce models for prediction of the yearly minimum flow in Binderup Å based on measurements of groundwater level in three wells. The linear regression model with the highest Nash-Sutcliffe Effeiciency amongst the developed models has a 95% confidence interval of 95 l/s and is based on groundwater level measured in February in well no. 26.1943. The neural network model with the highest NSE is based on measurements of groundwater level in February, January and December in the three wells 34.492, 26.1943 and 26.536. This model has a 95% confidence interval of 61 l/s. The study of a simple habitat modelling concept is based on a comparison between a habitat model with cross sections and modelled water levels from the National Water Resources Model for Denmark and a habitat model with cross sections and water levels measured for this project. This study concludes that with the available data, the simple habitat model is adequate for further modelling in this project. The simple habitat model concept is then used to produce habitat models for three life stages of trout for sections of Binderup Å. These models can be used to evaluate the habitat area at different flows, including the effect of flow reductions from increased groundwater abstraction.

A master thesis from Aalborg University

Prognosebaseret vandindvinding og modeller for vandløbspåvirkning

[Prediction Based Groundwater Abstraction and Models for Habitat Assessment]