Identification of uncertainty sources in distributed hydrological modelling: Case study of the Grote Nete catchment in Belgium

The quest for good practice in modelling merits thorough and sustained attention since good practice increases the credibility and impact of the information, and insight that modelling seeks to generate. This paper presents the findings of an evaluation whose goal was to understand the uncertainty in applying a distributed hydrological model to the Grote Nete catchment in Flanders, Belgium. Uncertainties were selected for investigation depending on how significantly they affected the model’s decision variables. A Fault Tree was used to determine various combinations of inputs, mathematical code, and human error failures that could result in a specified risk. A combination of forward and backward approaches was used in developing the Fault Tree. Eleven events were identified as contributing to the top event. A total of 7 gates were used to describe the Fault Tree. A critical path analysis was carried out for the events and established their rank or order of significance. Three measures of importance were applied, namely the F-Vesely, the Birnbaum, and the B-Proschan importance measures. Model development of distributed models involves considerable uncertainty. Many of these dependencies arise naturally and their correct evaluation is crucial to the accurate analysis of the modelling system reliability.Keywords: distributed hydrological models, Grote Nete, MIKE SHE, uncertaint

The rainwater harvesting strategy for Uganda

This paper is a review of the study carried out to develop a national strategy for rainwater harvesting (RWH) in Uganda. RWH has been practiced over years although it had been treated as a ‘third-class’ water source in government policies and investment plans. The study assessed hindrances to utilisation of rainwater as one of the major sources, and the strengths that could be taken advantage of to promote its use. Seven districts in different climatic zones and regions were used for this study. RWH is possible throughout Uganda. However, the availability of suitable roofs varies between 28% and 95% for different areas. Affordable storage was modelled in different areas for household and communal facilities. RWH was recommended to increase safe water coverage where this is deemed low. The study recommends government participation in piloting investment in RWH, and provision of training support and subsidies

Responding to global challenges in food, energy, environment and water: Risks and options assessment for decision-Making

We analyse the threats of global environmental change, as they relate to food security. First, we review three discourses: (i) ‘sustainable intensification’, or the increase of food supplies without compromising food producing inputs, such as soils and water; (ii) the ‘nexus’ that seeks to understand links across food, energy, environment and water systems; and (iii) ‘resilience thinking’ that focuses on how to ensure the critical capacities of food, energy and water systems are maintained in the presence of uncertainties and threats. Second, we build on these discourses to present the causal, risks and options assessment for decision-making process to improve decision-making in the presence of risks. The process provides a structured, but flexible, approach that moves from problem diagnosis to better risk-based decision-making and outcomes by responding to causal risks within and across food, energy, environment and water systems

Assessment of the effect of change in land use and rewetting on catchment hydrology

The increasing awareness and concern about the potential impact of anthropogenic changes on river valley ecosystems have led scientists to realize that mankind’s economic strides made over the last two centuries were at the expense of the earth’s biodiversity, its environment, and the stability of its self-regulatory systems. This is resulting in a number of initiatives being planned to reverse past anthropogenic changes, of which, river valley rewetting is one. In this study, spatially distributed hydrological modeling was used to test for the response of the catchment’s hydrology and peak river discharge to alternative methods of implementing river valley rewetting. The Grote Nete catchment was taken as the study area. It is a middle-sized catchment located in the northeast of Flanders. The basin area of the outlet limnigraphic station at Varendonk is 385km2. Distributed hydrological modeling of the Grote Nete catchment was undertaken using MIKE SHE. MIKE SHE was chosen for its ability to generate a spatially distributed representation of the catchments’ hydrological processes, which was necessary for undertaking scenario analyses. A multi-criteria calibration protocol was used for model development. The land use modelling and spatial analysis was carried out using the spatial analysis tool, SPAN. A qualitative identification and evaluation of uncertainty in the context of the distributed hydrological modeling was undertaken, along with a study on the importance of river network representation in model development. A detailed discussion is presented on the unsuitability of most available land use maps for direct use in specific modeling applications, and how this challenge was overcome during this study. An evaluation was undertaken to understand the applicability and limitations that could be expected in the scenario analysis of rewetting. The study generated river valley rewetting scenarios in which consideration was made of the type and location of the wetlands. The study confirmed that different types of wetlands have many possible interactions with hydrology. The study found rewetting by infiltration restoration to be a catalyst for the greatest decrease in total river discharge. This was achieved through a decrease in the paved overland component of river discharge, and an increase in the saturated zone flow component. The greatest increase in discharge resulted from taking no rewetting action. In the event that no rewetting action is taken in the catchment, the return period of extreme river discharges is expected to reduce by nearly 4% which means that extreme river discharges will become more frequent in the future. It was determined that the scenarios with the two highest changes in return period of extremes are infiltration restoration and upstream valley bottom wetlands, respectively. It was established that the return period of extremes was decreased by 2.8% for upstream headwater wetlands. In analyzing the results the study, it was established that for any given scenario, a positive change in paved overland flow component of river discharge was accompanied with a negative change in baseflow + overland flow. Relationships were also established indicating the change in return period of peak river discharge varied with changes in discharge components, across the various scenarios. Some recommendations of the study were that: an interdisciplinary study approach continue to be adopted for rewetting studies; a similar procedure be followed in using land use information during future studies; the type and location of the wetlands be considered whenever modeling rewetting by wetlands restoration; research be undertaken into wetland classification methods, and wetlands’ hydrological behavior; and field data be obtained from the Grote Nete catchment for at least two or three years of the simulation period, and used to verify the output of the scenario simulations.Table of Contents ACKNOWLEDGEMENTS I ABSTRACT XV INTRODUCTION 1 1.1 MOTIVATION AND GENERAL OVERVIEW 1 1.2 RIVER VALLEY REWETTING 3 1.2.1 Definition and background 3 1.2.2 Runoff infiltration in the Grote Nete 5 1.2.3 Hydrological concerns regarding rewetting 5 1.3 WETLAND STATUS AND RESTORATION 7 1.4 HYDROLOGICAL MODELING 7 1.4.1 Physically based distributed models 8 1.4.2 Lumped/ conceptual models 9 1.4.3 Model development 9 1.4.4 Limitations of numerical models 12 1.5 STRUCTURE OF THE THESIS 13 METHODOLOGY AND MATERIALS 16 2.1 INTEGRATED CATCHMENT MANAGEMENT APPROACH 16 2.2 MODELING ENVIRONMENT 17 2.2.1 MIKE SHE 18 2.2.2 Land use modeling and spatial analysis 20 2.2.3 WETSPRO tool 22 2.2.4 ECQ tool for extreme value analysis 27 2.3 THE STUDY AREA 28 2.4 GROTE NETE NUMERICAL MODEL DEVELOPMENT 31 2.4.1 Time series input data analysis 31 2.4.2 Modelling of evapotranspiration 33 2.4.3 Saturated Zone model 41 2.4.4 Unsaturated Zone flow 43 2.4.5 Overland flow 45 2.4.6 Land use, vegetation, and soil type 46 2.4.7 River network 51 2.4.8 Model simulation control 55 2.5 MODEL PERFORMANCE EVALUATION 56 2.5.1 Model testing 56 2.5.2 Calibration and validation of Grote Nete model 58 IDENTIFICATION AND EVALUATION OF UNCERTAINTY SOURCES 60 3.1 INTRODUCTION 60 3.1.1 Uncertainty 62 3.1.2 Uncertainty sources in distributed modeling 62 3.2 MATERIALS AND METHODS 63 3.2.1 Model selection criteria 63 3.2.2 Uncertainty sources identification 63 3.3 RESULTS 64 3.3.1 Uncertainty sources: Importance evaluation 64 3.4 DISCUSSION 68 3.4.1 Uncertainty sources 69 3.4.2 Gates 69 3.5 CONCLUSIONS 72 SCENARIO ANALYSIS ON REWETTING 74 4.1 INTRODUCTION 74 4.1.1 Ecosystem-based river basin management 75 4.1.2 Land use mapping and classification 76 4.1.3 Application and limitations in scenario analysis 77 4.1.4 Concept of scenario design 82 4.2 METHODOLODY IN SCENARIO ANALYSIS 85 4.2.1 Land use maps of the Grote Nete 85 4.2.2 General approach of scenario generation 87 RESULTS AND DISCUSSION 96 5.1 RESULTS OF DISTRIBUTED MODEL DEVELOPMENT 96 5.1.1 Analysis of model calibration 96 5.1.2 Analysis of model validation 105 5.1.3 Analysis of second validation of model 115 5.2 DISCUSSION AND COMPARATIVE ANALYSIS 125 5.2.1 Filtered components of discharge 126 5.2.2 Efficiency coefficients, EF 126 5.2.2 Mean square error, MSE 127 5.2.3 Discharge, Rainfall, Area analyses 127 5.3 RESULTS OF SCENARIO ANALYSIS ON REWETTING 135 5.3.1 Reclassification of Grote Nete land use maps 135 5.3.2 Characteristics of Grote Nete land use maps 138 5.3.3 Properties of rewetting scenarios 143 5.3.4 Modeling output from the scenarios 147 5.3.5 Results of extreme value (EV) analyses 158 5.3.6 Average water content in the root zone 161 5.3.7 Discharge components and phreatic level 163 5.4 RIVER NETWORK REPRESENTATION AND COMMENT ON FUTURE MODEL DEVELOPMENT 167 5.4.1 Investigation into the importance of river network representation 167 5.4.2 Remarks on future model development 171 5.4.3 Remarks on scenario generation 175 GENERAL CONCLUSIONS AND RECOMMENDATIONS 177 6.1 SCENARIOS FOR RIVER VALLEY REWETTING 181 6.2 MODELING OF RIVER VALLEY REWETTING 183 6.3 RECOMMENDATIONS 184 REFERENCES 187 CURRICULUM VITAE OF ENG. RUBARENZYA MARK HENRY 212status: publishe