How should river embankments be spatially developed, from the upstream section or the downstream section?

Abstract

Using an economic model of how river embankments affect local residents, we explore the efficiency of embankment construction from two viewpoints:(1) which section of a river should be constructed first, the upstream or downstream section, and (2) how tall the embankments should be constructed depending on the section. For this purpose, we first develop a model to determine efficient construction of embankments using a hydraulic model. Then, we perform numerical simulations, which are calibrated with recorded ground data for the Kitakami and Abukuma Rivers. The results reveal that the construction from the upstream section can be efficient if the upstream section has a much larger population than the downstream section. We show that constructing higher embankments in the upstream section generates negative externalities in the downstream section because it increases the possibility of flooding in the downstream section. In addition, when the amount of inflow from tributaries into the downstream section is sufficiently large compared to that into the upstream section, embankments with efficient heights bring about Pareto improvements, giving benefit to residents in the downstream section as well as the upstream section. Moreover, we show that the efficient embankment heights depend on which section the construction starts from. K E Y W O R D Scost-benefit analysis, flood control planning, kinematic wave method, river embankments, spatial developments | INTRODUCTIONRecently, due to torrential rains probably associated with climate change, serious flood damage has occurred in various regions all over the world. For example, in Japan, recent torrential rains, such as the "2020 July Rains" and the "2019 East Japan Typhoon," have caused rivers to overflow and cities to be inundated, resulting in disasters. In Europe, in July in 2021, huge river floods in the Rhine river basin due to torrential rains caused the death of over 180 people. Such torrential rains are supposed to be caused by climate change. So, there is a possibility that the number of flood disasters will increase in the future.

Desain Tanggul Sebagai Solusi Banjir Dengan Model Hidrodinamik Nufsaw2d Pada Desa Maen, Sulawesi Utara

“…Hal ini pada prinsipnya sejalan dengan saran yang diutarakan pada studi yang dilakukan oleh (Makahinsade et al, 2020) yang menyatakan bahwa perlu dibangun tanggul pada semua ruas Sungai Maen Kecil untuk mencegah luapan banjir. Satu hal yang juga tak kalah pentingnya untuk dievaluasi adalah prioritas pembangunan tanggul (jika dilakukan secara bertahap) harus memperhatikan faktor seperti segmen mana yang harus dibangun terlebih dahulu (hulu atau hilir), sebagaimana yang dikaji oleh (Koma et al, 2022). Akhir kata, penulis berharap agar hasil penelitian ini dapat memberikan gambaran khususnya kepada para pemangku kepentingan (stakeholder) terkait, sehingga Desa Maen yang bebas banjir dapat terwujud.…”

Flood risk research for improving flood risk outcomes

“…Combining laboratory tests and subsequent numerical modelling analysis, they have been able to analyse and isolate the key engineering features (e.g., air-inflated air pressure of the dam, anchoring depth, dam height) of the temporary structure as well as the conditions (e.g., flood type and forces) that it will effectively perform. Koma et al (2023) adopt a more economic analytical approach to identify the optimum spatial construction of embankments considering the height of different sections and their priority of construction. Adopting an economic approach that focuses on which approach to construction is most efficient presents policymakers and flood risk professionals with evidence-based decision-making.…”