Modelling different flood mitigation measures using SWAT model and comparison of hydrological results with public perception : master thesis

Graham, Hannah Claire (author), Bezak, Nejc (mentor), Šraj, Mojca (comentor)

Under an increasingly variable future of weather extremes induced by global climate change, increased flooding and associated risks are a stark new reality. The August 2023 floods in Slovenia, with millions of euros worth in damage and 6 deaths, is just one recent example with the news increasingly abundant in such reports from around the world. It is against this backdrop that careful and urgent attention needs to be directed to what mitigation measures could and should be adopted to reduce this risk. The debate between the effectiveness of nature-based solutions (NBS) and other measures is hotly contended. There is much uncertainty in terms of the money, resources and focus that goes into these measures. In order to assess and compare the effectiveness of green, hybrid and grey measures on mitigating the flood risk in terms of reducing the peak discharge and flood peak, and increasing the lag time, a case study of the Gradaščica river catchment was selected. Wetland, retention polder and dam scenarios were developed to illustrate these measures by modelling them using the SWAT+ hydrological model, with a focus on the August 2023 flood event. This analysis showed that wetlands had only a minor effect on reducing the flood risk, whereas retention polders and dams were both able to significantly affect the discharge peak at the Dvor gauging station and the flood volume, as well as to increase the lag time, with dams being particularly effective. Following this hydrological assessment, a public perception analysis was done using data collected from a survey across Slovenia, the Czech Republic and the Netherlands. The survey data was analysed using the Kruskal-Wallis test and a Canonical Correspondence Analysis (CCA) was done to assess the factors that were influencing the public perception results. With a specific focus on Slovenia, and comparing across the general public and three expert groups – water engineers, researchers in the field of flood or water management, and agricultural workers – it was found that there were perception discrepancies between the groups. In general, the public overestimated the performance of green measures, whilst grey measures were considered most effective but least feasible. Comparing the hydrological and public perception results, it was found that most groups rated the grey measures the highest and green measures the lowest in terms of effectiveness, matching the order of hydrological results, although the researchers had a directly opposing view. This study concluded by highlighting the importance of multidisciplinary approaches to flood risk management and how hydrological models could provide more compelling, data-driven illustrations that could aid public in their perception of risks and risk mitigation, to allow for well-informed decisions to be made that are best suited to that particular catchment.

• Language: English
• Keywords: civil engineering, master thesis, flood risk management study, floods, SWAT+ hydrological model, nature-based solutions (NBS), flood mitigation measures, public perception, multidisciplinary approach
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Place of publishing: Ljubljana
• Publisher: [H. C. Graham]
• Year: 2024
• Number of pages: IX, 69 str., [18] str. pril.
• PID: 20.500.12556/RUL-160974-3a16d563-6779-3534-fd76-6ccba6ead612
• UDC: 556:627.51(043.3)
• COBISS.SI-ID: 206645763
• Publication date in RUL: 06.09.2024

Secondary language

• Language: Slovenian
• Title: Modeliranje različnih vrst protipoplavnih ukrepov z modelom SWAT in primerjava hidroloških rezultatov z javnim mnenjem : magistrsko delo

Abstract

V prihodnosti, ko bodo vremenski ekstremi zaradi podnebnih sprememb vse bolj spremenljivi, so vse pogostejše poplave in z njimi povezana tveganja nova realnost. Poplave v Sloveniji avgusta 2023 z več milijonov evrov škode in šestimi smrtnimi žrtvami so le eden od nedavnih primerov, saj so novice z vsega sveta vedno bolj polne takšnih poročil. V tem kontekstu je treba pozornost usmeriti v to, kateri ukrepi za zmanjšanje tega tveganja so najučinkovitejši. Razprava o učinkovitosti rešitev, ki temeljijo na naravi (NBS), in drugih ukrepov je zelo aktualna. Veliko je negotovosti glede sredstev in pozornosti, ki se namenjajo tem ukrepom. Da bi ocenili in primerjali učinkovitost zelenih, hibridnih in sivih ukrepov pri zmanjševanju poplavne ogroženosti v smislu zmanjšanja maksimalnega pretoka ter povečanja časa zakasnitve, je bila v nalogi izbrana študija primera porečja Gradaščice. Za ponazoritev teh ukrepov so bili razviti scenariji mokrišč, zadrževalnikov in večjih pregrad, ki so bili modelirani s hidrološkim modelom SWAT+, s poudarkom na poplavnem dogodku avgusta 2023. Izvedena analiza je pokazala, da imajo mokrišča le majhen vpliv na zmanjšanje poplavne ogroženosti, medtem ko lahko zadrževalniki in večje pregrade vplivajo na konico pretoka in obseg poplav na merilni postaji Dvor ter povečajo časovni zamik med največjo količino padavin in konico pretoka, pri čemer so bile pregrade še posebej učinkovite. Po tej hidrološki oceni je bila na podlagi podatkov, zbranih z anketo v Sloveniji, na Češkem in Nizozemskem, opravljena analiza javnega mnenja. Podatki iz ankete so bili analizirani s KruskalWallisovim testom, za oceno dejavnikov, ki so vplivali na rezultate zaznavanja javnosti, pa je bila izvedena CCA analiza. S posebnim poudarkom na Sloveniji in primerjavo med splošno javnostjo in tremi skupinami strokovnjakov - vodnimi inženirji, raziskovalci na področju poplav ali upravljanja voda ter kmetijskimi delavci - je bilo ugotovljeno, da med skupinami obstajajo razlike v zaznavanju učinkovitosti posameznih ukrepov. Na splošno je javnost precenila učinkovitost zelenih ukrepov, medtem ko so bili sivi ukrepi ocenjeni kot najučinkovitejši, vendar najmanj izvedljivi. Pri primerjavi rezultatov hidroloških raziskav in analize javnega mnenja je bilo ugotovljeno, da je večina skupin glede učinkovitosti najbolje ocenila sive ukrepe, najslabše pa zelene, kar se ujema z vrstnim redom hidroloških rezultatov, čeprav so bili raziskovalci nasprotnega mnenja. Na koncu te raziskave je bil poudarjen pomen multidisciplinarnih pristopov k obvladovanju poplavne ogroženosti in kako bi lahko hidrološki modeli zagotovili prepričljivejše, na podatkih temelječe ilustracije, ki bi javnosti pomagale pri dojemanju tveganj in njihovega zmanjševanja ter omogočile sprejemanje dobro informiranih odločitev, ki so najbolj primerne za določeno porečje.

• Keywords: gradbeništvo, magistrska dela, FRM študij, poplave, obvladovanje poplavne ogroženosti, hidrološki model SWAT+, na naravi temelječe rešitve (NBS), protipoplavni ukrepi, javno mnenje, multidisciplinarni pristop