scholarly journals A Conflict between Traditional Flood Measures and Maintaining River Ecosystems? A Case Study Based upon the River Lærdal, Norway

Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1884
Author(s):  
Ana Juárez ◽  
Knut Alfredsen ◽  
Morten Stickler ◽  
Ana Adeva-Bustos ◽  
Rodrigo Suárez ◽  
...  
Keyword(s):  
Remote Sensing Data ◽  
Freshwater Ecosystems ◽  
River Channel ◽  
Flood Mitigation ◽  
Mitigation Measures ◽  
Flood Events ◽  
Protection Measures ◽  
River Ecosystems ◽  
Hydraulic Models

Floods are among the most damaging of natural disasters, and flood events are expected to increase in magnitude and frequency with the effects of climate change and changes in land use. As a consequence, much focus has been placed on the engineering of structural flood mitigation measures in rivers. Traditional flood protection measures, such as levees and dredging of the river channel, threaten floodplains and river ecosystems, but during the last decade, sustainable reconciliation of freshwater ecosystems has increased. However, we still find many areas where these traditional measures are proposed, and it is challenging to find tools for evaluation of different measures and quantification of the possible impacts. In this paper, we focus on the river Lærdal in Norway to (i) present the dilemma between traditional flood measures and maintaining river ecosystems and (ii) quantify the efficiency and impact of different solutions based on 2D hydraulic models, remote sensing data, economics, and landscape metrics. Our results show that flood measures may be in serious conflict with environmental protection and legislation to preserve biodiversity and key nature types.

A conflict between traditional flood measures and maintaining river ecosystems. A case study in river Lærdal, Norway

2021 ◽  
Author(s):  
Ana Juárez ◽  
Knut Alfredsen ◽  
Morten Stickler ◽  
Ana Adeva-Bustos ◽  
Sonia Seguín-Garcia ◽  
...  
Keyword(s):  
Remote Sensing Data ◽  
Cost Effective ◽  
Freshwater Ecosystems ◽  
Mitigation Measures ◽  
River Ecosystems ◽  
Salmon River ◽  
River Bed ◽  
Ecological Scale ◽  
Hydraulic Conditions ◽  
Restoration Measure

<p>Floods are among the most damaging natural disasters which are likely to increase with the effects of climate change and changes in land use. Therefore, rivers have been the focus of engineering for establishing structural flood mitigation measures. Traditional flood infrastructure, such as levees and dredging have threatened floodplains and river ecosystems and during the last decade, sustainable reconciliation of freshwater ecosystems is increasing. However, we still find many areas where these traditional measures are proposed and it is challenging to find tools for evaluations of different measures and quantification of the possible impacts. We propose the use of hydraulic modelling and remote sensing data for evaluation of different flood strategies and quantification of changes in hydraulic parameters in an ecological scale. This is applied in Lærdal River, in Norway, a national salmon river specially recognized by its environment for Atlantic salmon, where the Norwegian Water Resources and Energy Directorate (NVE) has proposed l flood measures that include confinement with walls and dredging in the riverbed. Results show that the constructing a higher wall could avoid dredging in the river bed resulting in a most cost-effective solution. Dredging could improve hydraulic conditions for juvenile salmon if applied as river restoration measure but channelization of the river would have big impacts in the river ecosystem.</p>

scholarly journals Flood Mitigation Techniques—A New Perspective for the Case Study of Adayar Watershed

2017 ◽  
Author(s):  
Vidyapriya V. ◽  
Ramalingam M.
Keyword(s):  
Drainage System ◽  
Flood Mitigation ◽  
Storm Water ◽  
Mitigation Measures ◽  
Complex Nature ◽  
Adjacent Area ◽  
Drainage Network ◽  
Flood Events ◽  
Water Drainage ◽  
Impervious Area

Mostly populous city like Chennai is subjected to frequent flooding due to its complex nature of natural and man-made activities. From the analysis of the past records of flood events of 1943,1976,1985,2005 and 2008,it has been observed Adayar watershed is subjected to cataclysmic flooding in low-lying areas of the city and its suburbs because of inoperativeness of the local drainage system, rainfall associated with cyclonic activity, topography of the terrain, encroachments along the floodplain, hugh upstream flow discharge into the river and the highly impervious area which blocked the runoff to flow into the storm water drainage. After looking into these problems of flooding, a study have been conducted on Adayar watershed to develop a 2D hydrodynamic model for the two scenarios of existing condition of storm water drainage network and revised conditions of storm water drainage network using high resolution Lidar DEM to assess the volume of runoff with respect to time and duration on flood peaks for the two flood events of 2005 and 2015.Secondly to develop a 1D flood model to predict the river stages during peak floods using MIKE 11 for the Adayar watershed. Thirdly to integrate the coupled 1D and 2D model using MIKEFLOOD for assessing the extent of inundation in the floodplain area of Adayar river. Finally results from the integrated model have been validated and the results found satisfactory. As a part of mitigation measures, two flood mitigation measures have been adopted. One measure such as revised storm water drainage system which enhances the flood carrying capacity of the drains and results in less inundated area which solves the problem of urban flooding and second measure such as regrading the river bed which reduces the floodplain inundation around the adjacent area of the river. After adopting these measures, the river is free to flow into the sea without any blockades.

scholarly journals Numerical simulation of runoff from extreme rainfall events in a mountain water catchment

2002 ◽  
Vol 2 (1/2) ◽  
pp. 109-117 ◽  
Author(s):  
J. Burguete ◽  
P. García-Navarro ◽  
R. Aliod
Keyword(s):  
Extreme Rainfall ◽  
Flood Mitigation ◽  
Mitigation Measures ◽  
Rainfall Runoff ◽  
Shallow Water Flow ◽  
Extreme Rainfall Events ◽  
Small Reservoir ◽  
Rainfall Events ◽  
Water Catchment

Abstract. A numerical model for unsteady shallow water flow over initially dry areas is applied to a case study in a small drainage area at the Spanish Ebro River basin. Several flood mitigation measures (reforestation, construction of a small reservoir and channelization) are simulated in the model in order to compare different extreme rainfall-runoff scenarios.

scholarly journals Evaluation of Green and Grey Flood Mitigation Measures in Rural Watersheds

2020 ◽  
Vol 10 (19) ◽  
pp. 6913
Author(s):  
Ranko Pudar ◽  
Jasna Plavšić ◽  
Andrijana Todorović
Keyword(s):  
Urban Areas ◽  
Risk Mitigation ◽  
Damage Model ◽  
Flood Mitigation ◽  
Mitigation Measures ◽  
Integrative Approach ◽  
Loss Reduction ◽  
Protection Measures ◽  
System 2 ◽  
Flood Protection System

Floods cause considerable damages worldwide and mitigation of their adverse effects through effective protection measures is needed. Along with the commonly applied “grey” infrastructure, “green” measures that can offer additional benefits, such as ecosystem services, are increasingly being considered lately. While the recent research tendencies are focused on the effectiveness and the value of green measures in urban areas, this paper presents a comprehensive financial evaluation of green and grey flood mitigation scenarios for a smaller rural watershed. A micro-scale damage model that builds on the hydrodynamic modeling of hazard, detailed asset identification, and damage assessment is presented and applied for evaluation of benefits from various flood mitigation measures in the Tamnava watershed in Serbia. Four scenarios are considered: (1) existing flood protection system; (2) green scenario involving new detention basins; (3) grey infrastructure enhancement by rising of the existing levees and diverting flood discharges; and (4) green-grey scenario that combines scenarios (2) and (3). The benefits (loss reduction) are the greatest with the green scenario and marginally higher with the combined green-grey scenario. The results suggest that for small rural watersheds, a holistic, integrative approach that includes both types of infrastructure can provide the most effective flood risk mitigation.

Evaluation of adapted hydrological flood routing approaches as a cost-efficient contribution for the assessment of nature-based flood mitigation measures

2020 ◽  
Author(s):  
Fabian Merk ◽  
Michael Neumayer ◽  
Sonja Teschemacher ◽  
Markus Disse
Keyword(s):  
River Restoration ◽  
Hydrological Model ◽  
Flood Plain ◽  
Flood Routing ◽  
Flood Mitigation ◽  
Mitigation Measures ◽  
Hydrological Models ◽  
Flood Events ◽  
Hydrodynamic Models ◽  
Cost Efficient

<p>Nature-based retention measures are an essential part of a sustainable and integrated flood protection strategy and can contribute to a holistic flood mitigation approach. Thereby river restoration measures such as channel widening, or flow path extension to increase the channel meandering represent successfully used components. Coupled with flood plain measures, retarding and retention effects of flood events are possible. These effects are commonly computed applying two-dimensional hydrodynamic modelling approaches. However, these developments rely on high spatial and temporal resolutions which are generally characterized by a high computational demand and are hence time and cost expensive. Thus, the evaluation and derivation of flood routing parameters to reproduce the resulting hydrodynamical processes in hydrological models can provide an effective and fast computation of river restoration scenarios.</p><p> </p><p>The objective in the present study is the derivation and application of flood routing parameters which can account for the effects of river restoration and flood plain measures in hydrological models. Further, this study aims to determine if the catchment and scale specific outcomes and parameter sets are also applicable to a broader range of catchments.</p><p>For this purpose, commonly applied flood routing approaches and the associated parameters used in hydrological models (e.g. the kinematic wave approach in the WaSiM model) are investigated for catchments of different scales in Bavaria (Germany) and for flood events of varying characteristics (e.g. return period, flood volume). To determine the effects of channel restoration and flood plain measures, two-dimensional hydrodynamic models (HYDRO_AS-2D) are set up to simulate the current state as well as restoration scenarios. Based on the simulation results of the hydrodynamic models, the parameters of the flood routing approaches are calibrated to match the catchment specific restoration effects for a first set of river sections. Catchment and scale dependent parameter sets (dominating valley type, flood plain slopes) are then derived to reproduce the specific river restoration. First results of the calibration of the parameter sets show a satisfying fit of the hydrological model to different restoration scenarios of the hydrodynamic model. For the validation of the derived parameter sets of the flood routing methods in the hydrological model additional river sections of the hydrodynamic models are subsequently investigated.</p><p>The implementation of the new flood routing parametrization of the hydrological models is finally examined as an alternative resource efficient way of calculating the effects of river restoration scenarios. Moreover, the applicability of the outcomes as a cost-efficient alternative compared to hydrodynamic models in land use planning and risk assessment is assessed and discussed within the frame of river restorations as flood mitigation measures.</p>

scholarly journals Comment on "Significance of "high probability/low damage" versus "low probability/high damage" flood events" by Merz et al. (2009)

2010 ◽  
Vol 10 (1) ◽  
pp. 1-2 ◽  
Author(s):  
C. M. Rheinberger
Keyword(s):  
Risk Aversion ◽  
Natural Hazards ◽  
High Probability ◽  
Flood Mitigation ◽  
Mitigation Measures ◽  
Flood Events ◽  
Flood Risks ◽  
Relative Damage ◽  
Low Probability

Abstract. This comment is meant to shed some light on the use of so-called "risk aversion functions" in the management of flood risks and other natural hazards as recently proposed in this journal (Merz et al., 2009). In particular, I resume the discussion as to whether the relative damage is a suitable indicator of risk aversion and lay out why the use of this indicator may lead to inefficient decisions upon flood mitigation measures.

Better use and management of levees: reducing flood risk in a changing climate

2015 ◽  
Vol 23 (2) ◽  
pp. 240-255 ◽  
Author(s):  
Caroline Wenger
Keyword(s):  
Flood Risk ◽  
Flood Risk Management ◽  
Flood Mitigation ◽  
Flood Events ◽  
Institutional Barriers ◽  
Detailed Review ◽  
Adverse Impacts ◽  
The Usa ◽  
Adaptive Approaches

Many nations rely on dykes and levees to mitigate flood risk. However, a myriad of problems has prompted views that levees are ultimately maladaptive and should be used as a measure of last resort. This leads to questions not only about the place of levees in future flood risk management, but also whether anything can be done to reduce their impacts. A detailed review of flood events from Australia, China, the Netherlands, and the USA was used to develop a case study for each country. Case studies present existing levee problems, future flood threats, and national strategies to address them. These were used as a basis to analyse the transferability of adaptive flood approaches. While many countries are attempting to restore floodplain storage, thereby reducing their reliance on levees, others are increasing their investment in levee construction. This review explores factors that affect the transferability of adaptive approaches, including issues, such as problem recognition, affordability, and program delivery. It was found that countries vary in their ability to recognise levee problems, and the level at which decisions are made influences the likelihood of adaptive solutions being adopted. Analysis suggests that federal systems face particular challenges and their capacity to adopt adaptive approaches may be impaired if institutional barriers are not addressed. Regardless of the overall approach to manage flood risk, the experiences of all case study countries offer some broadly applicable lessons for improving the use and management of levees, reducing their adverse impacts, and improving the integration of natural flood mitigation.

scholarly journals Socio–Economic Analysis of Riverine Flooding on Low-Income Dwellings: Adayar River, a Case Study

2020 ◽  
Vol 30 (2) ◽  
pp. 133-157
Author(s):  
Suriya Saravanan ◽  
Mudgal Basavaraj ◽  
Prakash Nelliyat
Keyword(s):  
Low Income ◽  
Flood Plain ◽  
Flood Damage ◽  
Vital Role ◽  
Flood Mitigation ◽  
Mitigation Measures ◽  
Structured Interviews ◽  
The Impact ◽  
Sustainable Mitigation

AbstractFlood damage assessment plays a vital role in providing information to policy developers. Nowadays, due to urbanization, the impact of flooding on communities is extensive, including tangible damage to property, the environment, and infrastructure as well as intangible damage due to stress, health hazards, and hardship. This paper provides an overview of a detailed flood assessment study conducted in the Kotturpuram Housing board area, located on the flood plain of the Adayar River in Chennai, India. A relatively simple approach to data collection was adopted, being a Questionnaire Survey (QS) as well as semi-structured interviews and observation techniques, due to data and research limitations. Losses due to damage to belongings and extra spending to buy essential commodities during flooding are also dealt with in this study. The flood mitigation costs for flooding that occurred in the year 2015 are also evaluated. A stage-damage curve was arrived at based on the information collected. Optimal and sustainable mitigation measures can be achieved only when the socio-economic aspects are adequately considered. Thus, this analysis was designed to estimate the effects of flooding on a community’s social and economic welfare, and thereby help to educate the community, including residents and officials, about the impact and magnitude of flooding. The outputs of the study will be the key inputs for designing flood mitigation and relief measures.

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