Cost–benefit analysis of flood mitigation measures: a case study employing high-performance hydraulic and damage modelling

Natural Hazards - This paper shows a detailed, advanced procedure to implement cost–benefit analyses (CBAs) in order to assess the effectiveness of flood mitigation measures. The town of Lodi...     

Assessment of flood mitigation through riparian detention in response to a changing climate – a case study

Considering that urban areas may suffer more substantial losses than riparian farmlands during floods, diverting floodwater into riparian areas for temporal detention is expected to mitigate flood damage in downstream urban areas. In this study, an assessment has been conducted to evaluate the effect of flood mitigation through riparian detention in response to a changing climate in the Tou-Chien River basin of Taiwan. An integrated 1D–2D flow model was used to simulate the movement of flood wave in the main stream and the overbank flow inundating into the nearby lowlands. Based on the numerical simulation results, the flooding extents in the basin corresponding to different return periods of flood using existing flood prevention infrastructures were investigated. A detention strategy by lowering the levee along the riparian farmlands was proposed to avoid severe flooding in the densely populated urban areas of the basin. Research findings showed that the proposed detention measure can completely protect the downstream areas from overbank flooding when a flood having 20-yr period occurs, and can effectively alleviate the downstream flooding area from 27.4 to \(7.6\,\hbox {km}^{2}\) for a flood possessing 200-yr period.     

Severity–duration–frequency curves in the mitigation of drought impact: an agricultural case study

Severity–duration–frequency (SDF) curves are very useful in the analysis of drought phenomena. Station-level information obtained from SDF curves can be interpolated to obtain severity maps for fixed return period, in order to jointly analyse the spatial variability of drought characteristics (e.g. severity, duration and frequency). This approach is limited because the severity is usually quantified through indices that use hydrological and meteorological data, depending on the type of requirements. Therefore, drought indices can only reflect hydrological conditions, but are unable to quantify economic losses associated with droughts. In other words, SDF curves do not allow effective quantification of the impact expected with a certain return period. This paper proposes the methodology drought economic risk assessment (DERA) as an approach that emphasizes the importance of the relationship between a generic drought index (which quantifies water deficit) and the economic impact of the failure to meet water demand. Using integrated SDF curves, this relationship enables drought severity and corresponding impacts to be mapped. This procedure was applied to agricultural droughts (sunflower crop) in Umbria Region (central Italy). The agricultural drought impact variable was identified by sunflower yield (Y); the economic impact variable by net benefit depletion (EL); and the drought index by Relative Severity Index (RSI), which is quantifiable by a soil–water balance model. The relationships Y = g(RSI) and EL = f(Y) were specifically determined. Using DERA, it was possible to derive curves for SDF, impact–duration–frequency, and economic losses–duration–frequency (ELDF), which were then used to map severity, impact and economic losses for the assigned return period and duration. From the ELDF curves, further information was obtained by mapping critical drought durations for the assigned return period and economic loss threshold. The case study supports the potential of the proposed approach, both in the planning and real-time management of drought effects.     

Multi-scenario flash flood hazard assessment based on rainfall–runoff modeling and flood inundation modeling: a case study

Flash flooding is one of the most devastating natural disasters in China. A quantitative flash flood hazard assessment is important for saving human lives and reducing economic losses. In this study, integrated rainfall–runoff modeling (HEC-HMS) and hydraulic modeling (FLO-2D) schemes were used to assess flash flood inundation areas and depths under 5-year, 10-year, 25-year, 50-year, 100-year, 200-year, 500-year and 1000-year rainfall scenarios in a mountainous basin (Hadahe River Basin, HRB) in northern China. The overall flash flood hazard in HRB is high. Under the eight rainfall scenarios, the total flooded area ranged from 6 to 8.73 km²; the flash flood inundation areas with depths of 1–2 m, 2–3 m, and over 3 m was 1.53–2.69 km², 0.63–1.44 km² and 0.33–1.11 km², respectively; and these areas accounted for 25.5–30.8%, 10.5–16.5% and 5.5–12.7% of the whole flooded area. The total flooded area increases rapidly with the return period increasing from 5 to 200 years, and the increase gradient slows when the return period is greater than 200 years. In the downstream area of HRB, the flash flood area with inundation depths greater than 1 m accounted for 54–71% of the flooded area under the eight scenarios. In comparison to other areas in the HRB, the downstream area is at the highest risk given its extensive inundation and substantial property exposure. The quantitative hazard assessment framework presented in this study can be applied in other mountainous basins for flash flood defense and disaster management purposes.

     

Landslide hazard and risk assessment: a?case study from the Hlohovec–Sered’ landslide area in south-west Slovakia

Landslide hazard or susceptibility assessment is based on the selection of relevant factors which play a role on the slope instability, and it is assumed that landslides will occur at similar conditions to those in the past. The selected statistical method compares parametric maps with the landslide inventory map, and results are then extrapolated to the entire evaluated territory with a final product of landslide hazard or susceptibility map. Elements at risk are defined and analyzed in relation with landslide hazard, and their vulnerability is thus established. The landslide risk map presents risk scenarios and expected financial losses caused by landslides, and it utilizes prognoses and analyses arising from the landslide hazard map. However, especially the risk scenarios for future in a selected area have a significant importance, the literature generally consists of the landslide susceptibility assessment and papers which attempt to assess and construct the map of the landslide risk are not prevail. In the paper presented herein, landslide hazard and risk assessment using bivariate statistical analysis was applied in the landslide area between Hlohovec and Sered?? cities in the south-western Slovakia, and methodology for the risk assessment was explained in detail.     

Different ways of landslide geometry interpretation in a process of statistical landslide susceptibility and hazard assessment: Horná Súča (western Slovakia) case study

The article draws a comparison between different ways of landslide geometry interpretation in the scope of the statistical landslide hazard and risk assessment processing. The landslides are included as a major input variable, which are compared with all of the input parametric factors. Based on the above comparison the input data are classified and the final map of landslide susceptibility is constructed. Methodology of multivariate conditional analysis has been used for the construction of final maps. Unique condition units was developed by combination of geological map (lithological units) and slope angle map. Lithological units were derived from geological map and subsequently reclassified into 22 classes. Slope angle map was calculated from digital elevation model (contour map at a scale 1:10,000) and reclassified into nine classes. As a case study, a wide area of Horná Súča (western Slovakia) strongly affected by landsliding (predominantly made of Flysch) has been chosen. Spatial data in the form of parametric maps, as well as final statistical data set were processed in GIS GRASS environment. Four different approaches are used for landslides interpretation: (1) area of landslide body including accumulation zone, (2) area of depletion zone, (3) lines of elongated main scarps, (4) lines of main scarp upper edge. For each approach, a zoning map of landslide susceptibility was compiled and these were compared with each other. Depending on the interpretation approach, the final susceptibility zones are markedly different (in tens of percent).     

Stability analysis and remedial measures of a landslip at Keifang,Mizoram – a case study

Landslips are often triggered due to non-engineered excavation of potential unstable slopes. Such slips can be stabilized by implementing suitable remedial measures.A landslip occurred at a drilling site of Oil India Limited in Mizoram State due to slope excavation. There was an immediate concern to protect the slope as the drilling platform and the highway at the top of the slope are at risk if further landslide occurs in future. Slope stability analysis of the failed slope was carried out to design suitable control measures for the protection of the slope from further sliding. Slope stability using various methods indicated that the slope is marginally stable. To improve the stability of the slope, suitable retaining structure at the toe of the slope was suggested and designed. Stability analysis performed with inclusion of retaining wall showed a significant increase in factor of safety of the slope. The suggested remedial measure has been implemented at the site and there is no landslip reported since then. The paper presents the results of the slope stability analysis and the design details of the retaining structure prescribed as the protection measure.     

Vulnerability assessment through index modeling: a case study in Muriganga–Saptamukhi estuarine interfluve,Sundarban, India

The coastal regions, deltas, and estuaries are severely affected by the sea level rise and cyclonic activities and climate changes. Sundarban delta is one of the most mysterious landscapes in the world, which has successively evolved due to sediment accumulation by the great Ganga and Brahmaputra river system. The area is characterized by low-lying islands and a flat topography coupled with macro-tidal activities, powerful surges, and seasonal cyclonic events. All these conditions put together this landscape defenseless to frequent flood and erosion. Since the last hundred years, the face of Sundarban has been changed remarkably from wildest to human-occupied territory by protecting this low-lying flat plain from tidal inundation through artificial embankment. In this background, the current study attempts to highlight the spatial extent and magnitudes of internal risk factors of the region using the composite vulnerability index. Coastal vulnerability defines a system’s openness to flood and erosion risk due to hydrogeomorphic exposures and socio-economic susceptibility in conjunction with its capacity/incapacity to be resilient and to cope, recover, or adapt to an extent. Coastal vulnerability assesses the potential risk from erosion and flooding of any low-lying coastal region due to its physiographical and hydrological exposures, socio-economic and political susceptibility, and resilience capacity. A natural system affects the socio-economic scenario of any region. Hence, multidimensional databases can be more effective to understand the extent of exposure, susceptibility, and resilience of any system. To throw some light on the situation of vulnerability of western estuarine Sundarban, between Muriganga and Saptamukhi interfluve, the composite vulnerability index has been carried out to delineate the magnitude and spatial extent of vulnerability with the help of quantitative techniques and geospatial tools. The estuarine tracts and coastal parts of the Ganga delta are two of the most densely populated areas in the world. The study highlights the critical situation of the population under different potential risk classes residing in the study area with the intention of suggesting some proper course of action of planning and management to conserve coastal communities in their original habitat.     

Integrated rainfall–runoff and flood inundation modeling for flash flood risk assessment under data scarcity in arid regions: Wadi Fatimah basin case study,Saudi Arabia

This paper presents a proposed integrated approach for flood hazardous evaluation in arid and semi-arid areas. Wadi Fatimah in Saudi Arabia is utilized for implementation of such an approach. The approach consists of four stages. In the first stage, a statistical analysis of rainfall data is performed to determine the design storms at specified return periods. In the second stage, geological and geomorphologic analyses are followed to estimate the geomorphic parameters. The third stage concerned with land use and land cover analyses linked with hydrological analysis to estimate the hydrographs. The fourth stage is related to the delineation of the inundation area under two scenarios: the presence and absence of the dam. The statistical analysis proved that some rainfall stations do not follow a Gumbel distribution. The presence of the dam reduces the inundation depth by about 10 %. The reduction in the inundation area due the presence of the dam is about 25 %.     

Mesozoic and Cenozoic structural deformation in the NW Tarim Basin,China: a case study of the Piqiang–Selibuya Fault

The Piqiang–Selibuya Fault is the most significant fault in the NW Tarim Basin, China. It has attracted increasing attention because of the discovery of a series of oil (gas) fields in and around the fault zone. The structural characteristics and evolution of the Piqiang–Selibuya Fault remain controversial. Field geological surveys and seismic data interpretation reveal that the fault has experienced three stages of activity. The thicknesses of the Permian and Miocene strata on opposing sides of the fault are clearly different, and these reveal that the fault has experienced two stages of significant thrusting. The first stage took place at the end of the Triassic and was associated with the Qiangtang Block amalgamated to the south margin of Eurasia. The second stage occurred at the end of the Miocene and might have been caused by the northwards overthrusting of the Pamir. These two stages of thrusting led to the lower–middle Cambrian detachment layer in the eastern part of the Keping thrust belt being 2 km shallower than in the western part. Since the Pliocene, the southern Tien Shan orogenic belt has been reactivated and thrust towards the interior of the Tarim Basin, and a series of ENE–WSW-trending thrust sheets have formed in the Keping thrust belt. Because of the different depth of the detachment layer on the opposing sides of the Piqiang–Selibuya Fault, the number and spacing of thrust sheets formed to the east of the fault differ from those to the west. This dissimilar deformation led to the strike–slip displacement on the Piqiang–Selibuya Fault. The three stages of fault activity record three important tectonic events in the NW Tarim Basin. Qualitative analysis of this activity helps us better understand the influence of the far-field effect of the collisions that occurred on the southern margin of the Eurasia plate on the structural deformation of the NW Tarim Basin.     

Water quality and risk assessment of dug wells: a case study for a poor community in the city of São Paulo, Brazil

Sparsely populated areas, or peripheral communities commonly lack access to a public water supply and sewerage systems. The inhabitants of these areas must make use of excavated wells to provide their water needs, and cesspits for domestic wastewater disposal. These on-site sanitation systems can release pathogens and nutrients into shallow groundwater. These poor communities urgently require cheap and efficient techniques for the detection of sanitary conditions, in order to prevent contamination of the water resources supplied by dug wells. The sanitary risk assessment methodology, applied in an irregular settlement south of the city of São Paulo, was based on a questionnaire with yes/no questions (risk factors), which allowed the identification of problems related to the well construction and operation, and the presence of potential contamination sources in its vicinity. These risk factors were compared against nitrate and bacterial analysis using the clustering statistical method, to verify the relationship between contamination and certain aspects surveyed in the questionnaire. Questions that were more related to contaminated wells were those concerning the presence of cover and its integrity; gaps between mouth and cover; the surrounding pavement and presence of ground irregularities; infiltration in the well casing; water-suspended materials; and proximity to contamination sources. Contamination models based on variograms allowed to observe that bacterial contamination presented a strong localized component, which was associated frequently with the way residents handled the wells, whereas nitrate contamination was related more to a regional (spatial) component; that is, the distance between wells and cesspits.     

Aquifer vulnerability assessment using GIS and fuzzy system: a case study in Tehran–Karaj aquifer,Iran

Aquifer vulnerability assessment techniques have been developed to predict which areas are more likely than others to become contaminated as a result of activities at or near the land surface. This research focuses on the evaluation of groundwater vulnerability to pollution in an urban area. Among several assessment methods, DRASTIC has been selected for this study. ArcGIS has been used to overlay and calculate different layers and obtain the vulnerability map. In order to show the importance of fuzzy algorithms in classification, both Boolean and fuzzy algorithms were used and compared. The fuzzy algorithm could recognize the areas with low and negligible vulnerability potentials whereas the Boolean model classified them as moderate. Two sensitivity tests, the map removal sensitivity analyses and single-parameter sensitivity analysis, were performed to show the importance of each parameter in the index calculation.     

Environmental study on a long history of Cu mining in Hubei, central China

The Tonglushan Cu mine situated in a densely populated, humid temperate ecoregional domain, so called the Birthplace of the Bronze age in the world, has been mined for over three thousand years. However, there is no significant pollution in surrounding area yet. To understand the mechanism controlling the environment the geological controls, including regional geology, deposit type, deposit size, host rocks, mineralogy, texture, alteration, ore controls, were studied by re-evaluating data from mineral exploration and mining activities; the geochemical factors including soils both in rice field and dry land, underground water and rice were investigated in 2003-2004. The results show that the ground water around the mine is not contaminated,     

Mechanism of water inrush driven by grouting and control measures—a case study of Chensilou mine,China

Water inrush into coal mines from aquifers underlying coal seams often causes serious casualties and economic losses. The key to preventing the disaster is to discover a water inrush mechanism suitable for specific geological and hydrogeological conditions and apply reasonable control measures. A case of the Chensilou mine is studied in this paper. Complex geological and hydrogeological conditions, such as 12 aquifers in the floor and small distance between coal seam and aquifer, make the mining face in the synclinal basin have a great risk of water inrush. In addition, as an important way to prevent the disaster, grouting will aggravate the risk of water inrush from the floor. The slurry will drive groundwater in the limestone aquifers L₈, even L₇ and L₆ along the horizontal (fracture zone in L₁₁~L₈) and vertical (Fs1 ~Fd1) water flow channel into the mining face and synclinal basin. A new water inrush mechanism driven by grouting is formed. In order to prevent this disaster, based on statistical law of hole deviation, the relative error of vertical depth and the angle between the borehole and the rock formation are obtained. Finally, an improved grouting method is proposed, which is useful to ensure the safe production of coal mine and reduce the cost of grouting.     

Implementation and evaluation of multivariate analysis for groundwater hydrochemistry assessment in arid environments: a case study of Hajeb Elyoun–Jelma, Central Tunisia

In most arid zones, groundwater (GW) is the major source of domestic, agriculture, drinking, and industrial water. Accordingly, the monitoring of its quality by different techniques and tools is a vital issue. The purpose of this paper is the evaluation of the combination of principal components analysis (PCA) and geostatistics as a technique for (1) identifying the processes affecting the groundwater chemistry of the detrital unconfined Middle Miocene Aquifer (MMA) of the Hajeb elyoun Jelma (HJ) aquifer (Tunisia) and (2) mapping the controlling variables for groundwater quality. This work is based on a limited database recorded in 22 wells tapping the aquifer and unequally distributed in the field. The proposed approach is carried out in two steps. In the first step, the application of PCA revealed that rock–water interaction, agriculture irrigation and domestic effluents could explain 85 % of the observed variability of the chemical GW quality of the MMA. As a result, two new variables are defined: V1 (rock–water interaction influence) and V2 (irrigation and domestic effluent influence). In the second step, the spatial variability of these variables over the extent of the MMA is mapped by applying a kriging interpolation technique. The results of this study suggest that, while both natural and anthropogenic processes contribute to the GW quality of the MMA, natural impacts can be considered as the most important.     

Assessment of microscale economic flood losses in urban and agricultural areas: case study of the Santa Bárbara River,Ecuador

Natural Hazards - To reduce and prevent significant economic flood losses, reliable tools are required to estimate potential river inundation effects. This paper focuses on the estimation of direct...