Mark Henry Rubarenzya

Modelling in support of an interdisciplinary approach to ecosystem restitution

Modelling in support of an interdisciplinary approach to ecosystem restitution This paper reports on a study being undertaken to analyze the potential effects of rewetting when undertaken for the restitution of the catchment ecosystem of the Grote Nete catchment. In bringing together the expertise of both ecological and hydrological modelers, this study aims at ensuring that the science being performed is immediately relevant from both the environmental management and the socio-political perspectives. Like many European catchments, Grote Nete has been experiencing an increase in extreme hydrological events. In addition, there has been a decline in the ecological value of the catchment ecosystem. The problem is considered to be a conflict of interests arising between urban/agricultural and nature conservation needs. Rewetting has been considered as a possible intervention to reverse these trends. However, a shortcoming with rewetting is that the hydrological consequences remain largely unknown. A numerical model has been developed to study these potential effects. A land use model, SPAN was developed and coupled to a physically-based, fully distributed model (MIKE SHE) to complete an ecohydrological model. The paper describes the development of the model. Wykorzystanie modelowania wielodyscyplinarnym podejściu do resytytucji ekosystemów Artykuł przedstawia badania przedsięwzięte w celu analizy wpływu zwiększenia wilgotności na potencjalne efekty odtworzenia ekosystemu zlewniowego rzeki Grote Nete. Gromadząc razem w jednym miejscu wiedzę ekspercką oraz doświadczenia twórców i użytkowników, zarówno modeli ekologicznych, jak i hydrologicznych, celem niniejszego artykułu jest ukazanie, iż zintegrowane badania naukowe są niezwykle istotne z punktu widzenia gospodarowania środowiskiem, jak i perspektywy społeczno-politycznej. Taka jak wiele innych europejskich zlewni, rzeka Grote Nete doświadcza w ostatnim okresie wzrastającej liczby ekstremalnych zjawisk hydrologicznych. Dodatkowo, wartość ekologiczna ekosystemu tej zlewni również systematycznie maleje. Jest to przyczyną pojawiania się problemów związanych z narastającym konfliktem interesów pomiędzy potrzebami rolniczo-urbanizacyjnymi a potrzebami ochrony przyrody. Zwiększenie wilgotności rozważane jest jako jedno z możliwych działań, które może przyczynić się do zatrzymania czy wręcz odwrócenia procesu degradacji ekosystemu zlewni. Jednakże pewnym ograniczeniem związanym ze zwiększeniem wilgotności jest to, iż jego konsekwencje hydrologiczne pozostają w dużym stopniu niewiadome. Model numeryczny został opracowany w celu poznania i oceny potencjalnych efektów procesu zwiększenia wilgotności w zlewni. Stworzony model SPAN, opisujący sposoby użytkowania ziemi na obszarze zlewni, został połączony z modelem fizycznym o parametrach rozłożonych (MIKE SHE) w kompletny model ekohydrologiczny. Niniejszy artykuł prezentuje proces opracowywania tego kompleksowego modelu wraz z wynikami jego kalibracji i weryfikacji dla zlewni Grote Nete.

Application of multi-criteria tool in MIKE SHE model development and testing

The water resources in the northern part of Belgium have been profoundly influenced by anthropogenic activities. Physical deterioration of rivers and their floodplains is common. In general, hydrometeorological disasters have grown to be the most significant natural disaster in terms of frequency, but also in terms of costs to human life and property damage. River valley rewetting is believed to influence the ecology positively, especially during the dry summer months. However, its hydrological influence on the catchment over the annual cycle remains unclear, especially with regard to the winter months. Thus, this research undertook to build an integrated catchment model for a part of northern Belgium in order to study the hydrological influence of rewetting. The paper details the development and testing processes of the model. It highlights the design of a multi-criteria protocol that was used to develop and test the model, the process of determining recession constants corresponding to base flow, interflow, and overland flow components, and the paradox of homoscedascity. It describes WETSPRO, which is a tool for time series analysis which incorporates a recursive digital filter for exponential recessions to split total rainfall-runoff discharges into three components namely, base flow, interflow, and overland flow. The paper presents the results of an implementation of WETSPRO in multi-criteria model development and testing, during which the following plots were utilized: Modeled vs. observed discharge maxima during (nearly independent) quick-flow hydrograph periods; Modeled vs. observed discharge minima during (nearly independent) base-flow or slow-flow hydrograph periods; Cumulative flow volumes; High flow extreme value statistics; Low flow extreme value statistics; and Discharge time series, with and without log-scale for the discharge. Using the multi-criteria protocol, a hydrological model was built. The flow recession constants were determined as approx. 12 hours for quick flow, and 2 months for slow flow. This model is being used to study the effects of anthropogenic changes on the catchment hydrology.

Modeling of soil hydraulic processes and base flow in Flanders

This paper presents findings from an investigation into catchment hydrological response to changing stimuli, including land use change, climate change, and river valley rewetting. It outlines the central role of groundwater modeling in the development of a physically based, fully distributed catchment model, which role was as a consequence of the stream flow composition. The paper also examines the influence of the catchment’s hydraulic characteristics on the discharge. The study area was the Grote Nete catchment, located in the northeast of Belgium. Numerical digital filtration established that base flow constitutes the dominant stream flow of the river network, accounting for over 60% of the flow, followed by interflow with 25%. It was thus, considered paramount that these flow components be modeled accurately. The paper also highlights two issues that were taken into consideration when characterizing the catchment model. Firstly, the experimental procedures for measuring the soil hydraulic characteristics are difficult and not very reliable. Secondly, the use of pedotransfer functions to derive the characteristics from more easily measurable characterizing properties of the soil is equally as unreliable. The Averjanov method was used for the model. This method contains an exponent, whose value had a direct influence on the percolation rate in the soil and thereby influenced the actual evaporation rate. The MIKE SHE model code was adopted to model the temporal and spatial variability of soils. In testing the model hypothesis, the research made use of discharge data. For implementing a multi-criteria calibration protocol, a tool was sought that incorporates a recursive digital filter for exponential recessions to split total rainfall-runoff discharges into its three component sub-flows, and is able to determine the recession constants for each component. WETSPRO, a tool for time series analysis, was adopted. The catchment model is now being used to study trends of anthropogenic changes on catchment hydrology.