Natural Floodplain Research Articles

Strategic Integration of Catchment Level Natural and Structural Methods of Sustainable Flood Management: A Case Study of River Wharfe Catchment Area

Water has a crucial place in the advent of humankind the flourishing of mega population centres, and is an essential source of food, water transportation, and irrigation. The anthropogenic activities in taming the natural water streams to the optimum benefit of human beings disturb natural flood plains, ecology and habitat. The channelisation of streams and hydromodifications in dams, barrages or reservoirs result in climatic variations locally/ regionally and impact transborder stream flow. Researchers have been endeavouring to restore the flood plains to their natural conditions. Still, huge hydromodifications and the development of megacities right in the flood plains or adjacent to the streams have resulted in irreversible disturbances to the natural lay of ground/ landscape. Therefore, to avoid flooding disasters, further structural interventions are undertaken to augment the natural flood prevention methods using advanced materials like cement concrete, steel, and polymers rather than increasing the emissions of greenhouse gases. Considering the strategic necessity of engineering structures as an integrated catchment level solution to augment the natural methods, the researchers/ engineers are now focussing on the use of sustainable, eco-friendly materials and demountable/ hydraulic structures to minimise the carbon footprints of hydromodifications and to decrease the obstruction to the natural flow of streams by using the flood prevention structures/ gates/ walls/ reservoirs only in case of disastrous flooding and otherwise keeping them unemployed during normal stream discharges. This study has been used to review sustainable flood management using natural and structural techniques in the Wharf River catchment in the UK, reviewing the existing research/ flood management schemes giving the pictorial coverage. The study suggests that natural flood management techniques have restricted application parameters and must be augmented by engineering structures to achieve effective flood management against heavy flooding. Low CO2 embodied greener infrastructure structural materials containing supplementary cementitious materials (SCMs) can be a beneficial option for an environmentally friendly flood management strategy.

Estimating catchment‐scale sediment storage in a large River Basin, Colorado River, USA

Estimating <scp>catchment‐scale</scp> sediment storage in a large River Basin, Colorado River, <scp>USA</scp>

Tolerance to drought and flooding events provides a competitive advantage for an invasive over a native plant species

Abstract Changes in precipitation patterns are one of the most pervasive components of climate change. It has been suggested that the increased frequency of extreme drought and flooding events could affect the outcome of competition between native and invasive plants. However, empirical evidence for this prediction remains scarce. We combined controlled experiments and field observations in a freshwater floodplain to assess how drought and flooding events affect growth and biomass production of a native and an invasive plant species, grown in monoculture and mixed culture. We used the native Panicum dichotomiflorum and the invasive Urochloa mutica, which are two common grasses that frequently grow in natural floodplains of the Neotropics. The experimental and observational data showed that biomass production, growth and relative dominance of the native species were higher under more stable water levels. By contrast, the invasive species had higher biomass production, growth and relative dominance under extreme drought and flooding conditions. Thus, extremes in precipitation can alter the relative dominance of the two species in favour of the invader. Our study provides comprehensive evidence that water‐level oscillations may negatively impact the performance of the native species, whereas they did not alter the biomass production and growth of the invasive species. Under stable conditions, faster growth of the native species may hinder successful establishment of the invasive species. However, under extreme drought and flooding events, the invader could be favoured. Although our findings are based on the outcome of the interaction between only one native and one invasive plant species, our results suggest that biotic resistance might be higher under stable water conditions.

Overlap relationship between the priority of land consolidation and the floodplain wetland potential in paddy field

AbstractEcosystems that offer several ecosystem services can be used as green infrastructure for human well‐being. In recent years, human activities have substantially engineered ecosystems to produce the desired ecosystem services. However, such efforts could lead to losses of other ecosystem services. Paddy fields are a seminatural ecosystem that can provide several ecosystem services other than rice production. Land consolidation in paddy fields aim to increase the efficiency of food production as a provisioning service, but it could depress the quality of wetland habitat as a supporting service. Recently, the Japanese government aimed to agricultural production with biodiversity conservation. Therefore, prioritizing a control strategy for future land consolidation is needed. Land consolidation work is effective for large areas and may incorporate the paddy field, previously a floodplain wetland that played a crucial role in regional biodiversity. However, land consolidation could result in the loss of this function. In this study, I investigated the spatial overlapping between land consolidation and paddy fields, which were previously natural floodplain wetlands in Kanagawa Prefecture, Japan. Here, terrain parameters and flow accumulation value (FAV), that can reflect wetland potential, along with the latest land use map, were used. The consolidation records in 1‐km cell for the whole of Kanagawa prefecture were used to test the hypothesis. Results showed that high FAV area with high wetland potential has large paddy fields and was heavily consolidated. Thus, there is need for drastic policy changes to align both food production and biodiversity in paddy fields in Japan.

Investigation of the Spatial Changes in Overbank Floodplains and Sedimentations on the Study Site of the Middle Tisza

River systems and their floodplains can be studied and evaluated according to different aspects. The natural processes of the Tisza were mostly influenced by the river training and levee construction works named after Vásárhelyi, as well as the main channel regulation works. After the construction of the embankments, the fluvial formation of the natural floodplains ceased, as these processes limited it to areas of the floodplain along the main channel. Another consequence of the river regulations is that the river is forced to deposit the sediment transported during the floods in this narrow floodplain causing increased filling up, so the role of floodplains in flood conveyance has increasingly been reduced. In this study, the author aimed to investigate the bed changes that occurred as a result of the river regulation works, as well as the sediment accumulation in the flood plain, focusing on a typical section of the Middle Tisza.

Interpreting floodplain heterogeneity: Using field data to understand unsupervised floodplain classifications

The dynamic environment of natural river floodplains creates spatial heterogeneity that influences floodplain functions. Diverse human activities have homogenized natural floodplains and reduced their functions across many river networks in the temperate latitudes. Consequently, quantification of floodplain heterogeneity is needed to understand patterns of spatial heterogeneity on diverse floodplains and to inform floodplain restoration. We use a novel approach of spatially connecting field and remotely sensed data in order to interpret the output of, and build upon, a previous unsupervised classification workflow. We apply the method to three rivers in the US Pacific Northwest and the Altamaha River in the southeastern US and compare our results to a previous study. We find that field classifications, relative topography, and NDVI are useful for interpreting results from the unsupervised classification workflow. The interpretations are visually interesting, but we propose that it is the heterogeneity within the groups that is vital to floodplain functioning. Natural floodplains in the Pacific Northwest and coastal Southeast have moderate to high evenness, moderate to high intermixing, and moderate aggregation; and aggregation and evenness similar to rivers in Colorado and Oklahoma, USA, but lower intermixing. We attribute lower intermixing at the Altamaha River to slower rates of lateral channel migration, and lower intermixing at the Hoh River to the different hydrologic and sediment regimes and less stable braided planform. The results show that the larger rivers in this study (Altamaha, Hoh, and Sol Duc Rivers) have spatial heterogeneity similar to beaver-modified and shortgrass prairie rivers in Colorado, whereas the more inland and smaller river (Lookout Creek) has spatial heterogeneity similar to the tallgrass prairie site (Sand Creek). From the results of an ad hoc sensitivity analysis, we suggest using the highest spatial resolution topographic data available, using aerial imagery/mosaics from the same sensor, and removing largest patch index from the suite of comparable indices. The metrics reveal similarities and differences between rivers in the United States, and indicate that discernable trends may arise from a meta study comparing heterogeneity from more rivers across the country.

A long-term case study indicates improvements in floodplain biodiversity after river restoration

Natural floodplains are complex systems embodying an interwoven network of biodiverse aquatic and terrestrial ecosystems. Many floodplains have been impaired and disconnected from the river, leading to declines in biodiversity. River restorations often affect floodplains, yet monitoring programs rarely investigate effects on floodplain organisms. This study examined a river restoration project, which improved river hydromorpholgy and partly reconnected the adjacent floodplain. We applied a ‘control–impact’ design to investigate changes in floodplain community composition and diversity four, six, eight, and ten years after the restoration of the Nidda River in central Germany. Investigated taxonomic groups included ground beetles, birds, dragonflies, and spiders. We examined trends of abundance, richness, Shannon diversity, Shannon evenness, and temporal turnover over time post-restoration by comparing restored sites to a non-restored control site. Abundance and diversity increased in bird, dragonfly, and spider communities after the restoration. Effect sizes between restored and unrestored sites were mainly positive, indicating that restoration benefitted the investigated taxonomic groups. However, initially high abundance and diversity numbers of ground beetles declined at the restored sites over time, indicating differing responses across taxonomic groups. Our study accentuates and underlines the necessity for ongoing post-restoration monitoring of both floodplain and aquatic biota.

Comparative analysis of information products of land cover types&#x0D; of high spatial resolution in mapping floodplain landscapes

Intrazonal floodplain landscapes in the southern Russia remain relatively unaffected by the direct impact of anthropogenic activity, while zonal steppe landscapes are almost completely plowed, and semi-desert and desert are subject to high pasture loads. At the same time, climatic changes and the regulation of river flow by hydroelectric dams lead to the redistribution of river flow, which leads to the degradation of floodplain ecosystems due to a decrease in the duration and height of the flood. The construction of hydraulic structures, including shafts, dams, and arrays of irrigated lands, contributes to the withdrawal of significant areas from the floodplain regime. Reducing the duration of high water and the areas of flooding during them entails an increase in the mineralization of groundwater and stabilization of their level, which negatively affects natural floodplain ecosystems. Similar trends of hydrological and climatic changes are characteristic of floodplain landscapes of rivers in the zone of insufficient moisture, for example, the Don and its tributaries, the Volga in its lower reaches, the rivers of Central Asia. For these reasons, it is important to monitor the condition of floodplain landscapes, one of the tools of which is mapping based on remote sensing data. The purpose of this work is to map the types of land cover of floodplain landscapes of the Lower Volga on the basis of thematic information products ESA GlobCover, ESRI WorldCover, FROM-GLC10 with a spatial resolution of 10 m and GlobCover30 (GLC30) with a resolution of 30 m. It has been established that the actual area of wetlands regularly flooded during floods is 48% of the area of the entire territory. The most accurate estimates of the areas of wetlands, reservoirs, meadows and forests were obtained from the data of the ESA GlobCover information product, which is associated with the use of not only Sentinel-2 optical satellite images, but also Sentinel-1 radar. ESA data is recommended for analyzing the state of floodplain landscapes in the zone of insufficient moisture.

Natural Floodplains Are Quickly Vanishing

From 1992 to 2019, 600,000 square kilometers of natural floodplains were lost globally due to land conversion.

Large wood supports Elwha revegetation by reducing ungulate browsing

IntroductionThe increasing number of dams approaching obsolescence drives a need for knowledge about riparian restoration associated with dam removal. Restoring woody vegetation on exposed reservoir beds following dam removal is essential to stabilizing sediment, reconnecting riverine and terrestrial systems, and providing future sources of shade, nutrients, and wood. Revegetation after dam removal on many rivers can be challenging due to rapidly drying sediment, low sediment nutrient content, and heavy ungulate browse pressure. Revegetation in Elwha River restoration, the largest dam removal to date, used large woody debris (LWD) to mitigate moisture and nutrient limitation but ungulate browsing has constrained woody plant growth in many coarse sediment deposits. We evaluated potential for LWD to reduce ungulate browsing following Elwha dam removal.MethodsWe studied LWD mitigation of browsing in the largest former reservoir and a comparable valley upriver with a natural floodplain. We measured browse intensity in randomly located plots stratified by four levels of LWD extent, from no LWD to complete LWD enclosure.ResultsLWD reduced browse intensity four-fold in the former reservoir, but only in plots fully surrounded by LWD. Partial LWD enclosure provided little browse reduction. We obtained similar results in the upriver valley, where browse intensity was somewhat lower except within wood clusters. Wood-mediated browse reduction was slightly greater in the former reservoir than in the upriver valley. Protection from browse was greatest for plant species preferred by ungulates.DiscussionThese results suggest forest restoration after dam removal can be expedited by surrounding young trees with large logs. Planting within LWD clusters or placing LWD clusters in restoration sites can facilitate establishment of forest islands in strategic locations. These forest islands can support dispersal of seeds and marine derived nutrients, reconnect established forest to the river, and potentially advance restoration by decades.

Beyond the Case Study: Characterizing Natural Floodplain Heterogeneity in the United States

AbstractWe use the five landscape ecology metrics of aggregation index, percentage of like adjacencies, interspersion and juxtaposition index, patch density, and Shannon's evenness index to assess spatial heterogeneity at 15 floodplains in the continental United States. Assessments are based on floodplain classes and patches delineated remotely using topography and vegetation. Floodplain reaches examined here represent diverse drainage areas, flow regimes, valley geometries, channel planforms, and biomes. We selected sites with minimal direct human alteration. Our objectives are to quantify floodplain spatial heterogeneity; evaluate whether statistically significant patterns are present; and interpret the statistical analyses with respect to the influence of lateral channel mobility and valley‐floor space available. We develop a conceptual model of the influences on lateral mobility and space available, and then test specific hypotheses derived from this conceptual model. These natural floodplains have a median aggregation index of 58.8%, median percentage of like adjacencies of 58.5%, median interspersion and juxtaposition index of 74.9%, median density of 1,241 patches/ha, and median Shannon's evenness index of 0.934 (n = 15). In other words, natural floodplains have moderate aggregation of classes, high evenness and intermixing of classes, and a wide range of patch densities. Drainage area, the ratio of floodplain/channel width, elevation, precipitation, total sinuosity, large wood volume, planform, and flow regime emerge as important variables to floodplain heterogeneity. These results highlight the influence of biotic‐abiotic interactions in shaping floodplain heterogeneity across diverse river corridors.

Human alterations of the global floodplains 1992–2019

Floodplains provide critical ecosystem services; however, loss of natural floodplain functions caused by human alterations increase flood risks and lead to massive loss of life and property. Despite recent calls for improved floodplain protection and management, a comprehensive, global-scale assessment quantifying human floodplain alterations does not exist. We developed the first publicly available global dataset that quantifies human alterations in 15 million km2 floodplains along 520 major river basins during the recent 27 years (1992–2019) at 250-m resolution. To maximize the reuse of our dataset and advance the open science of human floodplain alteration, we developed three web-based programming tools supported with tutorials and step-by-step audiovisual instructions. Our data reveal a significant loss of natural floodplains worldwide with 460,000 km2 of new agricultural and 140,000 km2 of new developed areas between 1992 and 2019. This dataset offers critical new insights into how floodplains are being destroyed, which will help decision-makers to reinforce strategies to conserve and restore floodplain functions and habitat.

Seed banks of rare Physostegia correllii (Lamiaceae) in Lady Bird Lake, Austin, Texas, U.S.A.

Rare species threatened by climate and land-use change may harbor seeds in soil seed banks for periods of time even if adults have disappeared from the site. Soil samples were collected from sites with current Phyostegia correllii populations and from sites with former populations in Lady Bird Lake (a reservoir of the Colorado River, Austin, Texas. A seedling emergence study was conducted under greenhouse conditions, and the presence/absence of seedling emergence was recorded for two years. Seeds germinated from the seed banks of all current and former colonies tested. The presence of seed banks in a historical site (Blunn Creek) of Physostegia correllii suggests that management to encourage the germination of seeds might help to encourage the establishment of populations of this species. The re-establishment of disturbance fugitives might be facilitated by removing overhanging ground vegetation or imposing water management regimes that mimic natural floodplain dynamics.

The ‘Deluge’ of 25 October 1822 in Genoa, Italy

The ‘Deluge’ of 25 October 1822 in Genoa, Italy

Quantifying floodplain heterogeneity with field observation, remote sensing, and landscape ecology: Methods and metrics

AbstractFloodplains provide numerous ecosystem services that depend on the spatial heterogeneity, or patchiness, of the floodplain. Direct and indirect human alterations of rivers can reduce floodplain heterogeneity and function, but relatively little is known of patterns of floodplain heterogeneity in natural, fully functional floodplains. We quantify floodplain heterogeneity at four sites in the United States with the objectives of (i) developing a method of combining field measurements and remote sensing data products to calculate integrative landscape‐scale metrics of floodplain spatial heterogeneity and (ii) demonstrating which metrics from landscape ecology are likely to be useful for identifying qualities of natural floodplains, differentiating floodplains, and inferring processes, based on a case study of three prairie floodplains and one beaver‐modified floodplain in the continental United States. We developed a new unsupervised classification workflow that combines field data, topography, and Sentinel‐2A imagery to create classified floodplains for all four field sites that could be used to calculate heterogeneity metrics. We identified six heterogeneity metrics for characterizing natural floodplain heterogeneity: aggregation index, interspersion and juxtaposition index, largest patch index, patch density, percentage of like adjacencies, and Shannon's evenness index, and these metrics capture both intermetric (variation in spatial heterogeneity between the floodplains) and intrametric variation (variation in the patterns of the metrics). Results show that natural floodplains have high evenness and interspersion and juxtaposition of classes, and we attribute this to natural flow and sediment regimes driving channel migration, erosion, deposition, vegetation succession, and active beaver modifications. Colorado floodplains show higher aggregation and lower fragmentation than the Oklahoma floodplain. We attribute this to the greater incision and lower hydrologic variability at the Oklahoma site.

Florix, an index to assess plant species in floodplains for nature conservation – Developed and tested along the river Danube

Natural floodplains are ecosystems with a diverse mosaic of habitats and site conditions, but also highly threatened due to anthropogenic pressures. Plant species occur in all habitat types and can indicate their value for nature conservation. To improve sustainable management of rivers and floodplains, several indices such as the River Ecosystem Service Index (RESI) have been developed. However, there are so far no assessment schemes for the entire range of floodplain plants. The common assessment approaches like biological integrity, achievement rates or threatened species (Red list), applying to other species groups or other ecosystems, are not appropriate in floodplains. Legal obligations and the need to restore floodplains clearly call for an index assessing the ecological value in a reference area which can be combined with a 5-scale assessment in accordance to established assessments like RESI or the Water Framework Directive.Five typical characteristics describing vascular plants’ adaptation to floodplain habitats were identified. These can be derived from published data sets available for all species in Germany. We checked these indicators for multicollinearity and selected three of them: species number, hydrodynamic indicators, nature conservation indicators. Species number highly correlate with habitat indicators and geographic occurrence. For the selected three indicators we determined thresholds to group habitats and their indicator rate to five classes (very low to very high value for nature conservation). These thresholds are valid for the river Danube and for the habitat types scrutinized in this study.The Florix approach was sensitive in data sets testing active against former floodplains and protected against unprotected areas: For the entire reference region ‘Danube floodplain’, Florix values were higher in the active floodplain and in the protected areas. Only the habitat type ‘water bodies’ showed better scores for habitats in the former floodplain, for ‘softwood forests’ the status of being part of a protected area had no effect. Florix results were validated in two case studies differing in land use intensity. The region with dominant agricultural use showed significantly lower values than that with a higher portion of forests and grasslands.Florix can be used for a floristic conservation status assessment at single habitat level or for the entity of a study region in comparison to a reference region. It allows to identify main pressures and to complement a habitat-type based evaluation. To achieve higher comparability, we should strive for a generalized monitoring in Europe like it is common in aquatic ecosystem monitoring.

Capitalization of reduced flood risk into housing values following a floodplain restoration investment

ABSTRACT Vast resources are allocated across the US and elsewhere for flood control in floodplains. Increasingly, these efforts involve restoring the function of natural floodplains to attenuate flood risk and provide a range of other ecosystem services. We investigated the capitalization of reduced flood risk from floodplain restoration into housing values in the city of Orting, Washington, USA. Our identification strategy exploits the occurrence of a major high-flow event directly following project construction, which demonstrated the ability of the widened floodplains to attenuate flooding. The prices of homes located within established 100-year or 500-year floodplains were discounted by 3%. Reduced flood risk associated with the floodplain restoration led to a 5% increase in the prices of homes in the 500-year floodplain on average. No evidence of reduced flood risk capitalization was found for homes the 100-year floodplain, where flood insurance rate maps and mandatory insurance requirements remained unchanged across the study period. The results suggest that reduced flood risk associated with floodplain restoration can capitalize into homes outside of designated high-risk zones.

New formulas addressing flow resistance of floodplain vegetation from emergent to submerged conditions

ABSTRACT Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied successfully for non-submerged conditions whereas its suitability for submerged conditions requires further development. This study investigates the vegetative flow resistance at low relative submergences and extends existing LAI-based approaches building upon new flume data and prior experiences from field-scale applications. We provide advanced LAI-based formulas for modelling the flow resistance from emergent to submerged conditions, with water depth up to three times higher than the vegetation height. Such low relative submergences are highly relevant in hydraulic analyses of riverbank and floodplain flows but not adequately represented in existing formulas. The use of the deflected vegetation height as the characteristic height provided the most accurate modelling results, whereas the use of undeflected height resulted in significant errors. As a new development for submerged conditions, we proposed von Kármán scaling factor for improved model predictions. Overall, the results proved that LAI-based modelling is suitable also at low relative submergences for a wide range of vegetation densities (LAI = 1–5) and mean flow velocities (0.05–1.2 m s−1). For both emergent and slightly overtopped vegetation the JAR and VAS approaches outperformed the BAPmod-LAI approach that does not account for reconfiguration. For modellers, we provide a workflow and guidance on the use of the newly developed LAI-based formulas in 1D/2D hydrodynamic models for both emergent and submerged conditions.

Hydrological Analysis and Statistical Modelling of Swat River Basin for Flood Risk Assessment

The climatic variations and anthropogenic activities in the river catchments worldwide are causing severe weather events and flooding. The narrowing down of natural floodplains/ channels, land-use changes, deforestation and mushroom urbanisation with unplanned infrastructure development are aggravating causes of severe storms and floods, especially in developing countries. Hydrological studies, flood modelling and statistical flood frequency analysis are considered imperative to assess the hazards/ risks of flooding and their mitigation measures. Estimating predicted storms/ floods for different return periods can give a reasonable idea about the frequency of storm events. This study analysed the Swat river basin to determine the predicted return periods with expected storm/ flood in its catchment and Swat river. The weather and rainfall in the Swat river basin remain unpredictable. Historically, it has seen peak precipitation of 150mm – 274mm and a super flood of 10050 m3/sec in 2010, more than its 200 years return period. Flood frequency and statistical analysis using Log Pearson 3 (LP3), Generalized Extreme Value (GEV) and Gumbel Maximum (Gumb-Max) on Easy Fit software and Log Pearson 3 equations have predicted weather instability in the Swat basin with the prediction of super flood like 2010 happening in 40 years return period. Construction of Swat expressway on elevated embankment will disturb the natural drainage pattern and likely result in inundation in flood plains due to inadequate capacity of cross drainage structures to withstand the spontaneous flash flooding. However, these have been designed on 100 years return period. However, probability density and hazard functions show a lesser probability of any mega hazard; therefore, cross drainage structures and crisscrossing channels in the river catchments may be planned on a minimum 100 years return period as an economic/ reasonable safe limit. Still, additional structural/ non-structural measures should augment these for efficient flood-fighting like plantation and maintenance of drainage structures, construction of small dams/ reservoirs for swift water management in case of a flash flood and placement of rescue/ relief resources at accessible points as per flood zoning.

Comparison of Urbanization, Climate Change, and Drainage Design Impacts on Urban Flashfloods in an Arid Region: Case Study, New Cairo, Egypt

Urban flooding is considered one of the hazardous disasters in metropolitan areas, especially for those located in arid regions. Due to the associated risks of climate change in increasing the frequency of extreme rainfall events, climate-induced migration to urban areas leads to the intensification of urban settlements in arid regions as well as an increase in urban expansion towards arid land outskirts. This not only stresses the available infrastructure but also produces substantial social instability due to unplanned urban growth. Therefore, this study sheds light on the main factors that are increasing the flood risk, through examining the consequences of rapid urban growth and the performance of drainage networks on urban flood volumes and comparing it with the effects induced by climate change on the surface runoff. The effect of urbanization is assessed through land use maps showing the historical urbanization conditions for the past 30 years, while considering the role of urban planning and its effect on exacerbating surface runoff. Six climate projection scenarios adopted from three Global Climate Models under two Representative Concentration Pathways (4.5 and 8.5) during the period (2006–2020) were compared to ground observed rainfall data to identify which climate scenario we are likely following and then evaluate its effects on the current rainfall trends up to the year 2050. The significance of the drainage design in the mitigation or increase of surface runoff is evaluated through capacity-load balance during regular and extreme storms. It is found that using impervious surfaces coupled with poor planning causing the blockage of natural flood plains led to an increase in the total runoff of about 180%, which is three times more than the effect induced by climate change for the same analysis period. Climate change decreased the intensities of 2- and 5-year rainfall events by 6% while increasing the intensities of extreme events corresponds to 100-year by 17%. Finally, the urban drainage had a distinguished role in increasing surface runoff, as 70% of the network performed poorly during the smallest rainfall event of 2-year return period. The study emphasizes the urgency to re-evaluate the existing and future urban drainage design approach: although urban development and climate change have inevitable effects on the increase in urban flood volumes, it could be alleviated through improved infrastructures.