Evolution of Flood Defense Strategies: Toward Nature-Based Solutions

Flood defense strategies have evolved from hard-engineered systems to nature-based solutions that advocate for sustainability to meet today’s environmental, social, and economic goals. This paper aims to analyze the historical progression and evolutionary trends in flood control strategies that have led to nature-based solutions. An evaluative literature review was conducted to narrate the evolution of nature-based flood management approaches for different flood types, river floods, coastal floods, and stormwater run-offs. The analysis reflected three evolutionary trends: the transformation of hard measures to soft measures; secondly, the increase in society’s attention to ecosystems and their services; and, finally, divergence from single-function solutions to multi-function solutions. However, continuous monitoring and evaluation of the previous projects and adapting to the lessons learned are the key to progress towards sustainable flood management strategies and their societal acceptance.

Vukovarska ada - (un)disputed part of the Serbian-Croatian border on the Danube

The Republic of Serbia and the Republic of Croatia, once (with the prefix "Socialistic") members of the Yugoslav federation, and today neighboring, sovereign, internationally recognized states, have a common border of two hundred and fifty-two kilometers, of which one hundred and thirty-eight kilometers along the Danube. The line of the border on the Danube is the subject of different interpretations by the two sides, which in practice leads to numerous problems, primarily in terms of navigation safety, prevention of migration, poaching, flood defense and other security challenges. One of the points of contention is Vukovarska ada, a river island over which both sides emphasize their sovereignty. In 2011, the local governments of Bac and Vukovar, in order to relax the situation and improve good neighborly relations, signed the Agreement on Friendship and Cooperation, and it significantly affected the actual position of Vukovar Ada. In this text, the author analyzes the historical circumstances and the current status of Vukovar Ada in the context of the future overall resolution of the issue of demarcation of Serbia and Croatia on the Danube, as well as in the context of the Bac-Vukovar Agreement, ie the possibility of applying a similar model with appropriate modifications applied to some other disputed part of the common border on the Danube

Early warning system prototype on torrential floods in mountainous areas based on the IoT

Bosnia and Herzegovina is predominantly mountainous country with many settlements located near rivers. The characteristic terrain and seasonal occurrences of large amounts of water, due to rainfalls or snowmelt, make Bosnia and Herzegovina a country at a constant risk of flooding. Although the weather and hydrological situation in the territory of BiH is monitored by two hydrometeorological services, one from the Republika Srpska and the other from the Federation of BiH, automatic measuring stations have been set on the main watercourses, while remote monitoring of distant mountain areas subject to sudden emergence of torrential waters has not been established. A prototype of an IoT based torrential floods early warning system presented in this paper could solve this problem, being capable of monitoring watercourses in remote and inaccessible terrain. This system may be set to function autonomously, or as an integral part of an existing flood defense system. The basic unit of the system is an automatic measuring station (AMS) based on an Arduino controller with appropriate sensors, modules and power supply. Being small in size and affordable, easy to manufacture and setup, autonomous in operation and capable of wireless data transmission, makes AMS suitable for applications where use of standard metering stations is not possible. Number of AMSs in the system may vary and depend on the size of territory and water basin being monitored. Web server with custom developed Web application collects, processes, analyses and distributes data, while access level is set in correspondence with real-life authorization levels within the organizational structure of the flood defense system. Implementation of such system may provide monitoring of the situation in inaccessible areas in the basin, and assessment of time remaining until the flood wave reaches populated places. This will provide enhanced situation awareness and an additional window of opportunity for timely notification, reaction and protection of the local population and material goods.

Microhabitats of planted sea wall strips used by pollinators and Orthoptera

As part of an Urban Buzz scheme, strips of teasel (Dipsacus fullonum) and greater knapweed (Centaurea scabiosa) have been established along a sea wall flood defense in the UK to provide a corridor of flower-rich habitat for pollinators such as bees and butterflies. The cutting of tall grassland and planting of dicotyledons also created a suitable short sward environment (c. 30 cm height) for Orthoptera nymphs in the establishment year (2018). However, by 2019, the grassland in the pollinator strips was taller (c. 75 cm) and suboptimal for grasshoppers; in contrast to Roesel’s bush-cricket (Roeseliana roeselii), which inhabited the taller vegetation in greater abundance. The progression to established grassland with flowering D. fullonum saw the pollinator strips attract significantly higher numbers of bees and butterflies than the floristically poor control strips. This small-scale study illustrates that pollinator strips can have multi-functional benefits for ecosystems beyond pollination, with Orthoptera of tall grassland (R. roeselii) likely to persist alongside planted wildflowers.

Modeling Storm Surge Attenuation by an Integrated Nature-Based and Engineered Flood Defense System in the Scheldt Estuary (Belgium)

There is increasing interest in the use of nature-based approaches for mitigation of storm surges along coasts, deltas, and estuaries. However, very few studies have quantified the effectiveness of storm surge height reduction by a real-existing, estuarine-scale, nature-based, and engineered flood defense system, under specific storm surge conditions. Here, we present data and modelling results from a specific storm surge in the Scheldt estuary (Belgium), where a hybrid flood defense system is implemented, consisting of flood control areas, of which some are restored into tidal marsh ecosystems, by use of culvert constructions that allow daily reduced tidal in- and outflow. We present a hindcast simulation of the storm surge of 6 December 2013, using a TELEMAC-3D model of the Scheldt estuary, and model scenarios showing that the hybrid flood defense system resulted in a storm surge height reduction of up to half a meter in the estuary. An important aspect of the work was the implementation of model formulations for calculating flow through culverts of restored marshes. The latter was validated comparing simulated and measured discharges through a physical scale model of a culvert, and through a real-scale culvert of an existing restored marsh during the storm surge.