Floodplain Zoning Research Articles

Floodplain Zoning and Mapping for Lower Kelani River, Sri Lanka

Flood risk mapping and floodplain zoning are emerging as practical tools to reduce flood damage. The study intended to develop floodplain zoning maps in the lower Kelani River basin using Flood frequency analysis and MIKE 11 modeling. Flood quantiles estimated for River gauging station at Hanwella and Lower Kelani basin have been used for the flood map developments. The river gauge at Hanwella to the estuary River strip has been considered for floodplain zoning using MIKE 11 modeling software. The hydrologic modeling was performed using MIKE 11 Nedbor Afstromnings Model (NAM), while the hydraulic modeling was performed using MIKE 11 Hydro-Dynamic (HD) model. MIKE 11 rainfall-runoff (RR) NAM calibration and validation Nash-Sutcliffe efficiency (NSE) results were 0.766 and 0.607, respectively. Similarly, coupled NAM and HD model on Mike-Zero platform calibration and validation NSE results were 0.917 and 0.871, respectively. The return period floods estimated to the Hanwella River gauge and Lower Kelani River basin have been availed to generate flood inundation maps. Finally, the flood plain zoning maps have been developed for the Lower Kelani River for 10-, 25-, and 50-year return periods. These maps can be use to limit cultivations and reduce crop losses during monsoons.

Elevating Pakistan’s flood preparedness: a fuzzy multi-criteria decision making approach

In South Asia, Pakistan has a long and deadly history of floods that cause losses to various infrastructures, lives, and industries. This study aims to identify the most appropriate flood risk mitigation strategies that the government of Pakistan should adopt. The assessment of flood risk mitigation strategies in this study is based on certain criteria, which are analyzed using the fuzzy full consistency method. Moreover, flood risk mitigation strategies are evaluated by using the fuzzy weighted aggregated sum product assessment (WASPAS) method, considering previously prioritized criteria. According to the results, lack of governance, lack of funding and resources, and lack of flood control infrastructure are the most significant flood intensifying factors and act as major criteria for assessing flood risk mitigation strategies in Pakistan. Adopting hard engineering strategies (e.g., dams, reservoirs, river straightening and dredging, embankments, and flood relief channels), maintaining existing infrastructure, and adopting soft engineering strategies (flood plain zoning, comprehensive flood risk assessment, and sophisticated flood modeling) are identified as the top three flood risk mitigation strategies by the fuzzy WASPAS method. The highest weight (0.98) was assigned to the adoption of hard engineering strategies to mitigate flood risks. The study introduces a novel dimension by analyzing the real-time impact of the unprecedented 2022 floods, during which approximately one-third of the nation was submerged. This focus on a recent and highly significant event enhances the study’s relevance and contributes a unique perspective to the existing literature on flood risk management. The study recommends that the government of Pakistan should prioritize hard engineering strategies for effective flood risk mitigation. It also recommends that the government should incorporate these strategies in the national policy framework to reduce flood losses in the future.

Morphometric analysis in the sub basins of the Kali River using Geographic Information System, Karnataka, India

Morphometric analysis serves as a crucial tool for quantitatively characterizing drainage basins and exploring the intricate relationships between hydraulic parameters and geomorphological characteristics. This study presents a comprehensive morphometric analysis of the Kali Subbasin in Karnataka, covering an area of 1175.45 km². Utilizing remote sensing data and GIS tools, we quantified various morphometric parameters, including stream order, stream length, bifurcation ratio, drainage density, stream frequency, form factor, and circularity ratio, to understand the basin's geomorphological and hydrological characteristics. The study area is classified as a seventh-order basin displaying a dendritic drainage pattern with a drainage density of 2.853 km/km². Notably, the bifurcation ratio ranges from 4.396 to 3, indicating low to moderate structural control within the basin. The subbasin's elongated shape, with an elongation ratio of 0.604 and a circularity ratio of 0.298, indicates moderate peak flow and high susceptibility to erosion. Relief parameters showed significant elevation variations, contributing to intense erosion and heightened flood risks in lower-lying areas. The study identifies the basin's transition to a mature geomorphic stage, evidenced by an escalating stream length ratio from lower to higher orders. These findings underscore the importance of tailored watershed management strategies, including floodplain zoning, retention basins, afforestation, and terracing, to mitigate flooding and soil erosion. The study's insights are crucial for developing effective, localized water resource management plans and enhancing the resilience of the Kali Subbasin to future hydrological challenges.

Quantifying the relative impact of hydrological and hydraulic modelling parameterizations on uncertainty of inundation maps

ABSTRACTFlood risk management strongly relies on inundation models for river basin zoning in flood-prone and risk-free areas. Floodplain zoning is significantly affected by the diverse and concurrent uncertainties that characterize the modelling chain used for producing inundation maps. In order to quantify the relative impact of the uncertainties linked to a lumped hydrological (rainfall–runoff) model and a FLO-2D hydraulic model, a Monte Carlo procedure is proposed in this work. The hydrological uncertainty is associated with the design rainfall estimation method, while the hydraulic model uncertainty is associated with roughness parameterization. This uncertainty analysis is tested on the case study of the Marta coastal catchment in Italy, by comparing the different frequency, extent and depth of inundation simulations associated with varying rainfall forcing and/or hydraulic model roughness realizations. The results suggest a significant predominance of the hydrological uncertainty with respect to the hydraulic one on the overall uncertainty associated with the simulated inundation maps.

A new bivariate risk classifier for flood management considering hazard and socio-economic dimensions

Identification of flood-risk dynamics is pivotal for refurbishing the existing and future flood-management options. The present study quantifies the marginal and compound contributions of hazard and vulnerability to flood-risk through an innovative concept of Risk-classifier, designed in the form of a 5 × 5 choropleth. The proposed framework is demonstrated at the finest administrative scale of village-level over Jagatsinghpur district in Mahanadi River basin, Odisha (India) for two-time frames: Scenario-I (1970–2011) and Scenario-II (1970–2001). An increase in high and very high hazard and vulnerable villages is noticed in Scenario-I, the majority of them lying in the coastal stretches (S-E region) and adjoining flood plains of Mahanadi River (N–W region). Scenario-I is characterized by the majority of hazard-driven and compound (both hazard and vulnerability) risk villages, while Scenario II is characterized by a majority of vulnerability driven-risk villages. For the vulnerability-driven risk villages, rigorous enforcement of policies and mitigation schemes are recommended, while for hazard-driven risk villages, enhancement of structural measures and flood-plain zoning should be exercised. Such exhaustive flood-risk information may serve as a valuable cartographic product for the civic authorities and stakeholders and help in prioritizing flood mitigation actions for improved environmental planning and management.

Flood Frequency Analysis of the Rapti River Basin using Log Pearson Type-III and Gumbel Extreme Value-1 Methods

ABSTRACT Flooding is a widespread, frequent and most disastrous natural hazard around the globe. Flood frequency analysis is a necessary step for floodplain zoning and planning of the dams, bridges, culverts, embankments and anti-erosion structures along or across a river. In the Rapti river basin, the flood frequency analysis has been performed using the annual maxima series of discharges recorded at Jalkundi and Birdghat (Gorakhpur) gauge and discharge (G/D) sites with the help of Log Pearson Type-III (LP-III) and Gumbel Extreme Value -1 (EV1) methods. The flood discharges at 25, 50, 100, 200, 500 and 1000 year return periods are lower at Birdghat than those at Jalkundi. Such a reverse scenario indicates storage of flood waters in the Rapti floodplain near and upstream of Birdghat G/D site. The Kolmogorov-Smirnov (K-S) and Anderson-Darling (A-D) tests have been applied on the annual maxima series of discharge data to identify the appropriate curve fitting models, namely LP-III and EV1. The goodness-of-fit analysis shows that the LP-III method is more appropriate for flood frequency analysis than the EV1 at above mentioned G/D sites.

Development of Regional Flood Frequency Relationship for Narmada Basin using Index Flood Procedure

Water Resources decision making problems such as flood plain zoning, design of hydraulic structures etc. are based on design flood estimate, defined as discharge for a specified probability of exceedance. Flood Frequency Analysis helps to estimate the flood value for a specific return period. This procedure requires sufficient length of observed data of floods on river gauging sites which many a time is not available. In India major rivers have very few gauging sites and their tributaries are mostly ungauged. When quantiles have to be estimated for ungauged sites, Flood Frequency Analysis is neither possible nor reliable. Regional Flood Frequency Analysis is the means to overcome such problems, reasonably quantifying flood estimates at desired frequencies for sites within a more or less hydrological homogeneous region. Narmada Basin located in central India covers an area about 98,976 sq. km, drained by a large number of tributaries, most of which are ungauged, has been considered as the case. Index Flood method utilizing Gumbel’s EV-1 distribution have been used in the present study to develop the Regional flood frequency relationship. The Annual Peak Flood data of 16 gauging sites of Narmada Basin, having record length of 12 to 17 years, is utilized for flood estimation. Flood frequency curves for the considered gauging stations are generated. Development of regional flood frequency relationship leads to the estimation of different return period flood.

Hydrological Disasters Management and Risk Assessment

In India, floods and droughts are recurrent hydrological phenomenon causing huge losses to lives, livelihood, properties and infrastructure due to non-uniformly distributed rainfall both in time and space leading to the dimensionally opposite problems of flood and drought in different parts of the country. Out of 3290 lakh hectares geographical area, 40 million hectares is prone to floods which show high risk, vulnerability and is one of the most common hydrologic extremes frequently experienced by our country. On the other hand drought has a varying frequency from once in two years to once in fifteen years. It has been observed that there is flood in one part of country and severe drought in the other part. Various short term and long term measures should be adopted to prevent and mitigate the consequences of floods and drought rather than causing damages and losses due to interfering of the natural processes. In this paper, drought and flood problems in India are highlighted along with some of the important management issues requiring immediate attention. Furthermore, it presents the recently developed non-structural techniques for flood forecasting, flood plain zoning, glacial lake outburst modeling and decision support system.

Should I stay or should I go? Mitigation strategies for flash flooding in India

Post-disaster rehabilitation and rebuilding efforts are oftentimes spearheaded by government agencies rather hastily, to meet the urgent demands of disaster survivors. However in the absence of pre-planning for disaster recovery, they may increase community vulnerabilities due to a break down in social ties and livelihood needs. There is a growing recognition that adhoc top down policies should be replaced with an understanding of the preferences and needs of disaster survivors. This research is aimed at gauging the intended mitigation strategies that survivors from the Himalayan region of North India expressed, following the devastating flash flooding in 2013. A semi-structured questionnaire was used to interview 316 residents from 17 villages in the State of Uttarakhand to measure demographic characteristics, risk perception, prior flash flood hazard experience, evacuation experience, damage to home, and intended structural (relocate/ building back better) and non-structural (investing time and effort in emergency planning or raising self-awareness and knowledge of threats knowledge) mitigation measures. Findings suggest that relocation is not a preferred mitigation strategy. Rather, an overwhelming majority of the respondents are interested in emergency planning at the household and village levels. Investing in revising and updating the plans at all levels of government, reviewing the existing forecasting and warning system and creating a robust risk communication plan with local input, strictly enforcing the provisions of Flood Plain Zoning Act, 2012, improving hazard awareness programs and creating village level task forces with direct linkages to the State Disaster Management Agency are some of the recommendations made.

Regional flood frequency analysis: comparison of L-moment and conventional approaches for an Indian catchment

A realistic estimation of flood magnitude for a given return period is essential for successful operation and economical design of pivotal hydraulic structures such as dams, reservoirs and spillways, bridges, small culverts, urban drainage systems, flood plain zoning, economic evaluation of flood protection projects, etc. The flood frequency analysis is generally used for flood estimation, entirely based on the assumption that the floods are random and the floods in future are supposed to bear similar statistical properties that have occurred in the past. If adequate data are available at-site flood frequency analysis is used, otherwise regional flood frequency analysis (RFFA) is preferred for flood estimation. The RFFA for various small and medium catchments of India with different approaches have been carried out and reported in the literature. The focus of the present study is to carry out the RFFA using different approaches i.e. conventional method and L-moment and comparing the results for the Krishna and Penner subzone 3(h) of India. It was found that the values of growth factors obtained by the conventional method are higher than those of L-moment methods, thus leading to conservative estimate of the peak floods.

Probability of flooding and vulnerability assessment in the Ajay River, Eastern India: implications for mitigation

Estimation of flood intensity for a desired return period is of prime importance for flood management through flood plain zoning. Flood frequency analysis enables estimation of the probability of occurrence of a certain hydrological event of practical importance by fitting a probability distribution to one that is empirically obtained from recorded annual maximum discharge and/or stage data. This case study considers the use of four probability distributions, namely Gumbel’s extreme value distribution (EV-I), extreme value distribution-III (EV-III), log-normal (LN) and Log-Pearson Type III (LPT-3) in flood modelling of monsoon-dominated Ajay River and illustrates the applicability of goodness of fit (GOF) and D-index tests procedures in identifying which distributional model is best for the specific data. Twenty-five years (1985–2009) of existing and estimated annual peak discharge (Q max) data have been used for analyzing the trend of flood occurrence. After identifying the best fit model, the peak gauge height data (h max) are then analysed combining with geographic information systems (GIS) for predicting flood affected area and preparing inundation map at a specific return period (T). Results of the study showed that the LPT-3 distribution is better suited for modelling flood data for Ajay at Nutanhat in West Bengal. The computed Q max for LPT-3 distribution are slightly higher as compared to the results obtained by EV-I, EV-III and LN which are used for vulnerability assessment. The analysis also predicts that the affected area will be ranging from 235 to 290 km2 in near future (at 25- to 200-year T). These findings provide clear picture for the pattern of hydrological fluxes and aftermath in the next decades in lower Ajay River Basin (ARB). Sustainable planning and developmental measures that consider the modelled pattern of hydrological fluxes of the study area were recommended for decision making.

Floodplain Zoning Simulation by Using HEC-RAS and CCHE2D Models in the Sungai Maka River

River flooding causes several human and financial casualties. It is necessary to perform research studies and implement subsequent actions consistent with the nature of the river. In order to reduce flood damage, floodplain zoning maps and river cross-sectional boundaries are important to nonstructural measures in planning and optimizing utilization of the areas around the river. Due to the complex behavior of the rivers during floods, computer modeling is the most efficient tool with the least possible cost to study and simulate the behavior of the rivers. In this study, one-dimensional model Hydrologic Engineering Centers–-River Analysis System and two-dimensional model CCHE2D were used to simulate the flood zoning in the Sungai Maka district in Kelantan state, Malaysia. The results of these two models in most sections approximately match. Most differences in the results were in the shape of the river.

Editorial: steps towards global flood risk modelling

Editorial: steps towards global flood risk modelling

El-Nino/Southern Oscillation (ENSO): Recent Evolution and Possibilities for Long Range Flow Forecasting in the Brahmaputra-Jamuna River

The El Nino-Southern Oscillation is the dominant pattern of short-term climate variation, and is therefore of great importance in climate studies. Some recent studies showed the teleconnection between stream flow and the El-Nino Southern Oscillation (ENSO) of the equatorial Pacific Ocean. This paper presents an overview of the relationship between ENSO and stream flow in the Brahmaputra-Jamuna and the potential for wet season flow forecasting. This seasonal forecast of stream flow is very invaluable to the management of land and water resources, particularly in Bangladesh to improve the predictability of severe flooding. Over the years, large investments have been made to build physical infrastructure for flood protection, but it has been proved that it is not feasible, both economically and technically, to adopt solely structural mitigation approach. The choice of non-structural measures in this country focused mainly on flood forecasting because many of the nonstructural measures including flood plain zoning, compulsory acquisition of flood prone land, relocation etc have also been proved inappropriate for Bangladesh. The aim of this research is to find out an effective and long-lead flow forecasting method with lead time greater than hydrological time scale, using El Nino-Southern Oscillation index. Some studies indicate that SST can be predicted one to two years in advance using several ocean/ coupled ocean atmosphere models, therefore the ability to predict flow patterns in rivers will be highly enhanced if a strong relationship between river discharge and ENSO exists, and is quantified. With this view, to assess the strength of teleconnection between river flow and ENSO, at first correlation analyses between ENSO indices of any year and wet season flow of that year have been done. Here sea surface temperature (SST) has been used as ENSO index. This correlation analysis demonstrates a noteworthy relationship between natural variability of average flow of the months July-August-September (JAS) of the Brahmaputra-Jamuna River with SST of the corresponding months. Then discriminant prediction approach, also known as “Categoric Prediction” has been used here for the assessment of long range flood forecasting possibilities. This approach will be able to forecast the category of flow (high, average or low) using the category of predictor (predicted SST) at a sufficient lead time. In order to judge the forecast skill, a synoptic parameter “Forecasting Index” has also been used. This discriminant approach will improve the forecasting lead-time while the hydrologic forecast through rainfall-runoff modeling could provide a lead time on the order of the basin response time, which is several days or so. As the Ganges–Brahmaputra river basin is one of the most populous river basins of the world and is occupied by some developing countries of the world like Bangladesh, any reduction in the uncertainty about the flood in the Brahmaputra-Jamuna River would contribute a lot to the improvement in flow forecasting as well as to the economic development of the country.

Peoples’ Perception on the Effects of Floods in the Riverine Areas of Ogbia Local Government Area of Bayelsa State, Nigeria.

Flooding is a situation that occurs when land that is usually dry is covered with water of a river overflow or heavy rainfall. Floods are among the most devastating natural disasters in the world, claiming more lives and causing more property damage than any other natural phenomena. In Nigeria, flooding and erosion constitutes the most critical elements of coastal hazards. Though not leading in terms of claiming lives, floods affect and displace more people than any other disaster; they also cause more damage to properties. At least 20% of the population is at risk from one form of flood or another. This study examines peoples' perception on the effects of flood in the riverine areas of the Ogbia Local Government Area of Bayelsa State. Flooding has profound effects on the area regarding: loss of properties, destruction of food crops, biodiversity loss, increased erosion, land and water pollution, spread of water borne diseases, reduction in economic activities, and in severe cases loss of lives and destruction of entire settlements, etc. The effects are occasioned by natural and human factors. Data were collected through questionnaire and interview methods. The chi-square statistical technique was used to analyse the data. The study indicates that: the people at the study area perceive the effects of flooding differently. Those that are married, and especially farmers, perceive floods to be destructive, while the single people, those that are employed in government offices, and the people of the kolo creek who are not seriously affected by floods perceive floods to be less destructive. Those who live along Ekole creek generally see floods as much more destructive than those far away from Ekole creek. These differences occur as a result of the difference in the levels of responsibilities, and occupational and terrain characteristics. However, there is a general perception that flooding is destructive to those who live by the river bank (flood plains). The study suggests a number of ways for ameliorating the devastating effects of floods. These approaches include: flood plain zoning, channelization, pilling and construction of dykes, encouragement of people to take up flood insurance, and setting up a flood victims' relief and rehabilitation fund to relieve the peoples' burden.

Assessing Adequacy of a Probability Distribution for Estimation of Design Flood

Estimation of design flood for a desired return period is of prime importance for safe design of hydraulic structures such as dams, spillways, bridges, culverts, urban drainage systems and flood plain zoning. Frequency analysis enables estimation of the probability of occurrence of a certain hydrological event of practical importance by fitting a probability distribution to one that is empirically obtained from recorded annual maximum discharge (AMD) data. This study deals with the fitting of Extreme Value Type-1, Gamma, 2-parameter Lognormal (LN2) and Log Pearson Type-3 (LP3) distributions to the AMD data; and examines the use of goodness-of-fit tests and diagnostic analysis in assessing the adequacy of suitable probability distribution for estimation of design flood. Results of the study showed that LN2 distribution is better suited for modelling flood data for Tapi at Burhanpur, Girna at Dapuri and Bori at Malkheda sites; and LP3 is the best for Purna at Lakhpuri.

FLOODPLAIN PLANNING BASED ON STATISTICAL ANALYSIS OF TILPARA BARRAGE DISCHARGE: A CASE STUDY ON MAYURAKSHI RIVER BASIN

Floods in the West Bengal are responsible for colossal loss of human life, crops, and property. In recent years, various measures of flood control and management have been adopted. However, flooding in such rivers like Brahmani profoundly challenges flood-hazard management, because of the inadequacy of conventional data and high spatio-temporal variability of floods. To understand flood hazards and environmental change it is imperative that engineers and hydrologists utilize historical and paleoflood records to improve risk analyses as well as to estimate probable maximum flood on rivers such as these in a highly flood-prone region(Parkar,2000). The flood frequency analysis, probable peak discharge analysis, its return period analysis and floodplain zoning based on ancillary data will help better management of flood in the Mayurakshi River basin situated in the districts of Birbhum and Murshidabad.

Ecological riverine floodplain zoning: Its application to rural floodplain management in the Murray—Darling Basin

Floodplain zoning is a procedure used to identify areas of varying flood hazard and has been used extensively as a precursor to land use regulation, a non-structural floodplain management measure. Conventional floodplain zoning is based on hydraulic and hydrological analytical techniques, but its application to riverine floodplain environments of the Murray—Darling Basin of Australia is problematic. This paper develops and applies an alternative, ecological approach to floodplain zoning, using biophysical features as flooding indicators. Three zones are identified: low-risk floodplain land, flood-prone land (which includes two sub-categories) and floodway land. Land use policies, based on a land use constraint principle, are then developed for each floodplain zone.

Cost‐Benefit Analysis of Flood‐Plain Zoning

The economic yield of a flood-plain zoning program is measured by cost-benefit analysis. The methodology entails the use of a probabilistic hydroeconomic model to evaluate expected flood damages with and without zoning. The application shows that this type of program, albeit cost-effective overall, may be unacceptable for various reasons to the various parties involved.

Relationship between alluvial soils and flooding in the Piedmont lowland of southeastern Pennsylvania

Regressions of 50‐ and 100‐year synthetic flood widths on widths of alluvial soils bordering the stream were computed with confidence intervals for data from streams in the Piedmont Lowland of southeastern Pennsylvania. These intervals were too wide to recommend use of alluvial soils in floodplain zoning in this gently rolling terrain. A rule of thumb of 2½ times the alluvial soils width was suggested for safe location of land uses for which flooding would be intolerable. Data for one of the minor soils indicated that some soils may delineate flood hazard areas better than others, but too few data were available for complete analysis.