Flood Reduction Research Articles

An AHP-based assessment of flood triggering factors to enhance resiliency in Dammam, Saudi Arabia

Assessing flood triggering factors and risk reduction approaches are increasingly critical policy issues, particularly in global south countries that suffer the highest human and economic losses resulting from flood disasters. In Saudi Arabia, several cities have been experiencing flash floods incessant incidences in recent times, especially in the coastal cities of Dammam and Jeddah and Riyadh, which is bounded by valleys. However, there is a dearth of studies on experts’ opinions to assess flash flood triggering factors and alternative approaches to mitigating the flash flood impacts. Therefore, based on an Analytic Hierarchy Process (AHP) questionnaire survey (n = 18), the objectives of this study are to explore experts’ opinions about the influence of specific climatic and non-climatic factors that trigger flash floods and the most effectual alternative approaches for reducing flash flood occurrence in the coastal city of Dammam. The findings indicate that rainfall has the highest likelihood of triggering flash floods with a priority weight of 32%, trailed by land use (19%) and slope (18%). Elevation and soil type were adjudged the least triggering factors with priority weights of 16 and 15%, respectively. Concerning flood reduction alternative approaches, drainage management (59%) is the most important alternative approach, followed distantly by disaster warning system (16%) and raising public awareness (15%). The study recommends drainage management, installing disaster warning systems, and raising public awareness in reducing flash flood disasters in the study area and the country at large.

Flood risk mapping of the Sukamahi Dam failure with overtopping scenario

Sukamahi dam at Cisukabirus river, part of the upper Ciliwung watershed, located at Bogor regency. Sukamahi dam was designed for flood reduction purposes, especially for the downstream region, e.g., City of Bogor, Bogor regency, City of Depok, and Jakarta. Sukamahi dam will give flood reduction 13.53 m3/s with probability exceeded 2 %, and time to concentration (tc) for peak discharge (Qp) at least 4 hours longer than existing condition. Despite providing the benefits of flood control, the construction of dams also has the potential to increase the risk, i. E if a dam fails due to overtopping. Based on the Sukamahi dam flood failure scenario, dam failure has the potential to occur if the bottom outlet ( tunnel) and spillway fail when flood discharge with a 1000 year return period or more occur. Modeling of Sukamahi dam failure using 2 D HEC-RAS with unsteady flow analysis from sta 0 + 000 to STA 8 + 500 produces a map of inundation area of 36.89 Ha. The flood flow velocity is reaching 8.43 m/sec with a maximum flood flow depth of 69.72 m.

Flood forecasting using quantitative precipitation forecasts and hydrological modeling in the Sebeya catchment, Rwanda

AbstractThe absence of a viable flood early warning system for the Sebeya River catchment continues to impede government efforts towards improving community preparedness, the reduction of flood impacts and relief. This paper reports on a recent study that used satellite data, quantitative precipitation forecasts and the rainfall–runoff model for short-term flood forecasting in the Sebeya catchment. The global precipitation measurement product was used as a satellite rainfall product for model calibration and validation and forecasted European Centre Medium-Range Weather Forecasts (ECMWF) rainfall products were evaluated to forecast flood. Model performance was evaluated by the visual examination of simulated hydrographs, observed hydrographs and a number of performance indicators. The real-time flow forecast assessment was conducted with respect to three different flood warning threshold levels for a 3–24-h lead time. The result for a 3-h lead time showed 72% of hits, 7.5% of false alarms and 9.5% of missed forecasts. The number of hits decreased, as the lead time increased. This study did not consider the uncertainties in observed data, and this can influence the model performance. This work provides a base for future studies to establish a viable flood early warning system in the study area and beyond.

Initial investigation of hydraulics engineering for flood mitigation: A case study in Krueng Aceh Sub-watershed

Problem of flooding in the Krueng Aceh Sub-watershed occurs almost every year, thus, the study is conducted. This article aims at the initial study of flood mitigation investigations in the Krueng Aceh Sub-watershed, which consists of an analysis of existing channel hydraulics and an ideal design plan at the study site for hydrological analysis of the Sub-watershed. In addition to the analysis of channel hydraulics, analysis of the safety factors of existing channel cliffs and plans is also carried out. In addition to flood mitigation in the form of redesigning existing canals, this article proposes the construction of an earth-embankment dam. In the analysis of this existing channel, discharge is obtained by 1098.857 m3/s. When compared with the design flood discharge for a period of 100 years, the channel discharge capacity cannot accommodate flood discharge. With the redesign of the channel, the storage capacity can accommodate the flood discharge with a safety factor of 2.804, greater than the existing channel of 2.711. Earth-embankment dam is proposed with a safety factor of 3.497. Further studies need to be done flood routing to find out how much the contribution of the dam reservoir to the reduction of flooding in the study area.

Pilot Application of Flood Management Techniques for Urban Planning in Smart Cities around Rivers - The Case of Busan Eco Delta Smart City -

Considering the recent trend of climate change and increased flood risk from urbanization, it is necessary to prepare for floods when developing a riverside city. Both of the national pilot smart cities in South Korea are located along the river, but the flood management technique based on the characteristics of smart city remain insufficient. This study presented flood management techniques for smart cities around rivers from urban planning perspective through the analysis of characteristics of domestic and foreign smart cities and applied the technique to the Busan Eco Delta Smart City as a pilot study. The study results confirmed the feasibility of the technique in smart city development in consideration of flood risk, which would help towards an effective and efficient flood reduction planning. Although the applicability of the technique in land use and building projects has been confirmed in this study, further review would be needed for the creation of housing complex and building adaptation.

Strengthening flood resilient development in malaysia through integration of flood risk reduction measures in local plans

The increasing flood hazards due to climate change and development pressures have called for the integration of disaster resilient attributes through holistic flood risk reduction measures in development plans. Strengthening flood resilience in development planning therefore is not only to prevent risk, but also to reduce vulnerability as well as inculcate preparedness to adapt and better respond to disaster. In Malaysia, the notion of disaster resilience has become a recent development agenda in response to disaster risks especially flooding since the country is highly prone to such hazard. Flood reduction measures have become the key elements in Malaysia’s development plans at all levels, but little is known about the range of such measures being integrated in local development plan, which is a statutory development plan that guides planning control decisions and enable local communities to participate in local development agenda. Therefore, this study seeks to analyse the extent to which flood risk reduction measures are being integrated into local plans in Malaysia towards flood resiliency. The study, however, is limited to qualitative approach based on literature and content analysis of selected local plans. The finding suggests that all studied plans have integrated most measures to avoid risk and reduce vulnerability although measures on disaster preparedness were inadequate. There is a need thus, to further strengthen disaster resilience measures in the local development plans to ingrain preparedness and adaptation with more inclusive participatory civil societies and stakeholders.

Factors impacting community’s prioritization towards the benefits of Sustainable Urban Drainage Systems: A case study of Nhieu Loc – Thi Nghe sub-basin, Ho Chi Minh City

Sustainable Urban Drainage System (SUDS) includes various drainage techniques designed to reduce the run-off flow, improve the water quality, and provide amenity or landscape features. However, selecting the appropriate SUDS technique depends on not only the technical characteristics but also the community's perception and preference. Therefore, this study aims to determine the impact factors on the probability of households' prioritization towards SUDS benefits in the context of Nhieu Loc - Thi Nghe sub-basin, including the benefits of flood reduction, environmental enhancement, and landscape improvement. Data processing methods used in this study consist of statistical tests and ordinal regression using SPSS software. The regression results show that the overall accurate prediction rate for the 3 priority levels of SUDS benefits ranges from 50% to 70%. Factors that statistically significantly influence the priority include household income, knowledge of SUDS, frequency of flooding, depth of flooding, the distance to the nearest park, the distance to the nearest water body, and the distance to the nearest flooded location. In particular, the proximity to the nearest park affects the priority choice for all SUDS benefits with the principle that households near the park will probably choose higher priority to SUDS benefits than those living further.

Preliminary research on sponge city concept for urban flood reduction: a case study on ten sponge city pilot projects in Shanghai, China

PurposeThis research aimed to determine the differences and similarities in each pilot project to understand the primary design forms and concepts of sponge city concept (SCC) projects in China. It also aimed to examine ten pilot projects in Shanghai to extrapolate their main characteristics and the processes necessary for implementing SCC projects effectively.Design/methodology/approachA literature review and field survey case study were employed. Data were mostly collected through a field survey in Shanghai, focusing on both the projects and the surrounding environment. Based on these projects' examination, a comparative method was used to determine the characteristics of the ten pilot SCC projects and programs in Shanghai.FindingsSix main types of SCC projects among 30 pilot cities were classified in this research to find differences and similarities among the pilot cities. Four sponge design methods were classified into ten pilot projects. After comparing each project size using the same geographical size, three geometrical types were categorized into both existing and new city areas. SCC project characteristics could be identified by combining four methods and three geometrical types and those of the SCC programs by comparing the change in land-use and the surrounding environment in ten pilot projects.Originality/valueThe results are valuable for implementing SCC projects in China and elsewhere and future research on the impact of SCC projects.

Flood mitigation in coastal urban catchments using real-time stormwater infrastructure control and reinforcement learning

Abstract Flooding in coastal cities is increasing due to climate change and sea-level rise, stressing the traditional stormwater systems these communities rely on. Automated real-time control (RTC) of these systems can improve performance, and creating control policies for smart stormwater systems is an active area of study. This research explores reinforcement learning (RL) to create control policies to mitigate flood risk. RL is trained using a model of hypothetical urban catchments with a tidal boundary and two retention ponds with controllable valves. RL's performance is compared to the passive system, a model predictive control (MPC) strategy, and a rule-based control strategy (RBC). RL learns to proactively manage pond levels using current and forecast conditions and reduced flooding by 32% over the passive system. Compared to the MPC approach using a physics-based model and genetic algorithm, RL achieved nearly the same flood reduction, just 3% less than MPC, with a significant 88× speedup in runtime. Compared to RBC, RL was able to quickly learn similar control strategies and reduced flooding by an additional 19%. This research demonstrates that RL can effectively control a simple system and offers a computationally efficient method that could scale to RTC of more complex stormwater systems.

On the Use of a Real-Time Control Approach for Urban Stormwater Management

The real-time control (RTC) system is a valid and cost-effective solution for urban stormwater management. This paper aims to evaluate the beneficial effect on urban flooding risk mitigation produced by applying RTC techniques to an urban drainage network by considering different control configuration scenarios. To achieve the aim, a distributed real-time system, validated in previous studies, was considered. This approach uses a smart moveable gates system, controlled by software agents, managed by a swarm intelligence algorithm. By running the different scenarios by a customized version of the Storm Water Management Model (SWMM), the findings obtained show a redistribution of conduits filling degrees, exploiting the whole system storage capacity, with a significant reduction of node flooding and total flood volume.

UAV and LiDAR Data in the Service of Bank Gully Erosion Measurement in Rambla de Algeciras Lakeshore

The Rambla de Algeciras lake in Murcia is a reservoir for drinking water and contributes to the reduction of flooding. With a semi-arid climate and a very friable nature of the geological formations at the lakeshore level, the emergence and development of bank gullies is favored and poses a problem of silting of the dam. A study was conducted on these lakeshores to estimate the sediment input from the bank gullies. In 2018, three gullies of different types were the subject of three UAV photography missions to model in high resolution their low topographic change, using the SfM-MVS photogrammetry method. The combination of two configurations of nadir and oblique photography allowed us to obtain a complete high-resolution modeling of complex bank gullies with overhangs, as it was the case in site 3. To study annual lakeshore variability and sediment dynamics we used LiDAR data from the PNOA project taken in 2009 and 2016. For a better error analysis of UAV photogrammetry data we compared spatially variable and uniform uncertainty models, while taking into account the different sources of error. For LiDAR data, on the other hand, we used a spatially uniform error model. Depending on the geomorphology of the gullies and the configuration of the data capture, we chose the most appropriate method to detect geomorphological changes on the surfaces of the bank gullies. At site 3 the gully topography is complex, so we performed a 3D distance calculation between point clouds using the M3C2 algorithm to estimate the sediment budget. On sites 1 and 2 we used the DoD technique to estimate the sediment budget as it was the case for the LiDAR data. The results of the LiDAR and UAV data reveal significant lakeshore erosion activity by bank gullies since the annual inflow from the banks is estimated at 39 T/ha/year.

Evaluation of the Main Function of Low Impact Development Based on Rainfall Events

Low Impact Development (LID) is one of the sustainable approaches to urban stormwater management in areas with rapid urbanization. Although LID has been shown to have a positive effect in flood reduction, the hydrological balance regulation effect of LID under a variety of rainfall events is not fully understood. In this study, we assessed the hydrological efficiency of LID at two residential–commercial mixed sites in Korea to investigate the main function of LID in terms of diverse rainfall characteristics. Storm Water Management Model (SWMM) was constructed to simulate the hydrological process numerical simulations in the pre-development, post-development and LID design scenarios, respectively. The model was calibrated and validated by using five observed rainfall–runoff events. Then, four single and four multiple LID practices (LIDs) were used to estimate their effectiveness under seven different designed rainfall events. The results indicate that LIDs substantially influence the hydrology cycle system, while the regulating effect varies with rainfall amounts. The efficiency of LIDs in flood reduction is proved to be more effective during lower storm events. However, LIDs should be designed to primarily prioritize the restoration of hydrological balance when the rainfall return period is longer.

The impact of Natural Flood Management on the performance of surface drainage systems: A case study in the Calder Valley

The evaluation of Natural Flood Management (NFM) has traditionally focused on the ability of interventions to mitigate downstream fluvial flooding by attenuating catchment response. However, the justification for the implementation of NFM projects at a local level is often supported by other benefits provided by such interventions (e.g. improvements to water quality or biodiversity). This study investigates the potential for a further, largely unrecognised, benefit. It is suggested that, by moderating water levels in downstream watercourses, upstream interventions could also help sustain free discharge from drainage outfalls, thereby improving the performance of urban surface drainage systems.A coupled modelling methodology is applied to the upper Calder Valley and the surface drainage in an area of the downstream town of Todmorden. The rural response and subsequent NFM interventions are characterised using hydrological (Dynamic TOPMODEL) and hydraulic (HEC-RAS) models. Several downstream surface drainage systems are then incorporated using an Infoworks ICM model to examine their response to changes in outfall inundation.The results suggest that catchment-scale tree planting and in-channel woody debris create modest benefits for downstream surface drainage systems. Under frequent storm events (e.g. a 1 in 10 year storm), the inundation of low-lying outfalls is completely removed. As storm severity increases (and surface flooding becomes an issue), impact from upstream NFM attenuation on outfall inundation durations diminishes significantly. However, the slight delay in rural response allows more water to escape surface systems, increasing the effective capacity of networks and reducing surface flooding. For instance, outfall inundation during an estimated 20 year event is delayed by 0.5 h, which results in up to 25% reduction in surface flood volumes.While the benefits are limited in extent, this modelling indicates that NFM can help improve downstream surface drainage performance.

Blue-green or grey, how much is the public willing to pay?

Flood reduction infrastructure is a vital aspect of many urban and peri-urban areas. To date, the majority of flood reduction projects use traditional “grey” materials and techniques. However, the use of blue-green infrastructures (BGI) is becoming more popular. This paper explores residents’ preferences for BGI or grey infrastructure projects to reduce flood risk. A discrete choice experiment using a split sample methodology was employed to determine if residents of the Carlingford Lough catchment in Ireland prefer either type of infrastructure to reduce flood risk. A random parameter logit was applied to the data. The results reveal that for the average person, they have a preference for flood risk reduction resulting in a flooding event once every 25 years rather than once every five years. The average respondent also holds a preference for BGI based solutions as opposed to a grey infrastructure solution. However, respondent living in a flood-prone area show no greater preference for a BGI solution.

Co-designed Land-use Scenarios and their Implications for Storm Runoff and Streamflow in New England.

Landscape and climate changes have the potential to create or exacerbate problems with stormwater management, high flows, and flooding. In New England, four plausible land-use scenarios were co-developed with stakeholders to give insight to the effects on ecosystem services of different trajectories of socio-economic connectedness and natural resource innovation. With respect to water, the service of greatest interest to New England stakeholders is the reduction of stormwater and flooding. To assess the effects of these land-use scenarios, we applied the Soil and Water Assessment Tool to two watersheds under two climates. Differences in land use had minimal effects on the water balance but did affect high flows and the contribution of storm runoff to streamflow. For most scenarios, the effect on high flows was small. For one scenario-envisioned to have global socio-economic connectedness and low levels of natural resource innovation-growth in impervious areas increased the annual maximum daily flow by 10%, similar to the 5-15% increase attributable to climate change. Under modest population growth, land-use decisions have little effect on storm runoff and high flows; however, for the two scenarios characterized by global socio-economic connectedness, differences in choices regarding land use and impervious area have a large impact on the potential for flooding. Results also indicate a potential interaction between climate and land use with a shift to more high flows resulting from heavy rains than from snowmelt. These results can help inform land use and development, especially when combined with assessments of effects on other ecosystem services.

Hydrological Risk Valuation on The Design of Sukamahi Dry Dam, Bogor, West Java

The flooding risk has always been considered as an important factor ofthe risk safety management of dams. The extreme flooding in the downstream of a dam could be either due to dam failure or sometimes without failure. In both cases, they give serious risks to people and property in the downstream of the dam.Sukamahi dry dam at Cisukabirus River is a part of the upper Ciliwung Watershed, located in Bogor regency. Sukamahi dry dam was design for flood reduction purpose especially for the downstream regione.g. Bogor City, Bogor Regency, Depok City and Jakarta. Sukamahi dam has a capacity in flood reduction of 13.53 m3/s with probability exceeded 2 %, and time to concentration (tc) of peak discharge (Qp) at least 4 hours longer than the existing condition. Construction of dry dam might increase the magnitude of flood prone risk especially on the dam breach caused by spillway capacity failure case, although with lower probability. Simulation using HEC RAS 4.1 and an ex-antehydrological risk valuation Xrisk model wereperformed with three scenarios, i.e. normal risk, risk averse and risk takers, with simplified option value and option risk calculation. Risk valuation can be used by decision makers to evaluate the technical and risk feasibility of Sukamahi dry dam construction.

Flood Control Reduction Analysis using HEC-RAS due to Local Floods in Central Jakarta

There are two types of floods in Jakarta: upstream flooding and local flooding. In general, floods in DKI Jakarta are caused by local floods. The main cause of this flood is the occurrence of high rainfall, poor drainage system, and land subsidence. This study will analyse the local flood that occurred in Gunung Sahari, Central Jakarta. Judging from the existing conditions, sedimentation occurs in the drainage channels. This sedimentation causes a reduction in the existing channel capacity. Based on a hydrological and channel capacity analysis, the existing drainage channels are designed based on annual rainfall i.e. return period 1-2 years, which is 133.10 mm/day. Flood modelling is done for existing conditions. Based on the results of modelling, floods that occur in locations between 50 cm - 100 cm. Due to dense housing conditions, widening and normalizing the channel is difficult. Therefore, flood reduction will be assisted by pumps. The pump will be installed in the downstream of the main drain, which is connected to Mati River. This pump is designed with a capacity of 0.5 m3 / sec. Based on the results of modelling, with a largest pump capacity of 0.5 m3/sec, flooding is only reduced by 5 cm - 7 cm. Due to the lack of effectiveness of the pump, retention ponds will be designed to reduce surface runoff. Retention ponds are designed with an area of 1 ha and a depth of 1.5 m. Modelling is done in the presence of a retention pond. With the addition of retention ponds, annual flooding for the 2-year return period on Gunung Sahari could be reduced. Therefore, the discharge that will be received by the drainage channel will be smaller than the capacity of the channel itself and the flood will be completely reduced.

Optimal Operation of Complex Flood Control System Composed of Cascade Reservoirs, Navigation-Power Junctions, and Flood Storage Areas

As more and more water projects are built on rivers, the flood control operation becomes more complex. Studies on the optimal flood control operation are very important to safeguard human life and property. This study focused on optimizing the operation of a complex flood control system composed of cascade reservoirs, navigation-power junctions, flood storage areas, and flood control points. An optimal model was established to jointly maximize flood peak reduction rates of downstream flood control points. A hybrid algorithm named the Dynamic Programming-Progressive Optimality Algorithm (DP-POA) was used to solve this model, and the middle and lower reaches of the Ganjiang River were selected as a case study. The results show that flood reduction at three downstream flood control points ranged from 1080 to 5359 m3/s for designed floods with different return periods, which increased by about 333~1498 m3/s in comparison with the conventional operation. Considering that the maximum water level of reservoirs using DP-POA and the conventional operation is the same, this indicated that DP-POA can make full use of the reservoirs’ flood control storage to reduce downstream flood peaks. In addition, the flood diversion volume of the flood storage area using DP-POA ranged from 0.33 × 108 to 1.79 × 108 m3 for designed floods with 200-year, 300-year, and 500-year return periods, which is smaller than that using the conventional operation.

Dynamic Trends of Urban Flooding Mitigation Services in Shenzhen, China

Urbanization is characterized by population agglomeration and the expansion of impervious land surfaces. As a result of ongoing urbanization, rain and flood events have increasingly affected the well-being of residents in cities across the world. This should draw attention to the role of urban ecosystems in providing runoff retention/flood mitigation services. Focusing on Shenzhen, a major city in southern China, we used a hydrologic model based on the Soil Conservation Service curve number (SCS-CN) model to evaluate this flood reduction ecosystem service and its dynamic trends based on long-term remote sensing data from 1980 to 2018. We find that Shenzhen’s capacity for flood reduction gradually decreased due to changes in land use. The spatial distribution showed strong reduction capacity in the eastern part of the city and weak capacity in the western part. Additionally, the city’s total flood reduction capacity decreased by over 1.88 × 108 m3 over the past two decades. This loss of ecosystem-based flood reduction capacity undermines Shenzhen’s resilience against extreme weather events. Due to climate change, Shenzhen should advance its plan to build a “Sponge City” rooted in the conservation, restoration, and construction of urban ecological spaces.

Efficiency of underground retention systems and reduction of urban floods in Tepic, Mexico

Many cities in Mexico experience recurrent floods, caused by changes in land use, the modification of surface and land runoff, the artificialization of areas initially intended for infiltration and recharge of groundwater and, in general, the insufficiency and deficiency of the local networks of urban drainage, incapable to evacuate the annual surpluses of precipitation. In this sense, the objective of this study evaluates the efficiency of an underground system of retention of rainwater in one of the main avenues of the city of Tepic, Mexico: Avenida Tecnologico. To this end, an analysis of the thematic contents and on-site inspection assisted by geographic information systems is carried out. Based on the systems approach and the logic of a qualitative model, it is concluded that the capacity of urban storm water networks for water evacuation is exceeded dimensionally. Also, it can be observed that retention systems can mitigate the urban entropy generated by the floods.