Preface

42 years ago, after graduating from the Hokkaido University, I was in my second summer at the Asahikawa River Office of the Asahikawa Development and Construction Department of the Hokkaido Development Bureau. In August 1981, when a historic flood occurred along the Ishikari River. This was the famous ‘81 flood. The tributaries I was working at the time, the Biei River and the Bebetsu River, meandered significantly, and the embankments were eroded from their foundations, drastically altering the appearance of the river in an instant. While I had learned about river meandering in hydrology classes at university, witnessing rivers rampage with the tremendous force of nature was a first for me.

The ‘81 flood prompted a revision of the master plan of the Ishikari River flood control. At that time, I was tasked with the river improvement planning for the upper reaches of the Ishikari River, particularly the planning of the Ushubetsu River diversion channel (now it’s called the Nagayama Shin River), a large-scale project. Although at that time, there was a sort of ambiguous era in river planning where the concept of “considering future changes in river channels” seemed to exist yet also appeared absent, after various considerations, I thought about the alignment of the diversion channel. I went to the main office in Sapporo to explain my proposed alignment, but it was swiftly dismissed and rewritten with a red pencil. There were no clear standards at the time, and there seemed to be no room for theoretical arguments. However, changing the plan meant redoing everything, from longitudinal and cross-sectional profiles to bridge designs, earthwork amount calculations, and rough estimates of construction costs, which meant countless sleepless nights of work would go to waste. Despite my desperate resistance, I had to accept the revision order, feeling frustrated for lacking convincing tools to persuade others.

From that time on, I began to think about whether it was possible to predict how the river flow and bed morphology would change based on its planform. Later, I was transferred to the Sapporo Civil Engineering Research Institute, CERI, and took charge of large-scale model experiments on the Ishikari River. Simultaneously, within the Ishikari River Large Model Experiment Committee, there were vigorous discussions about the river morphology change of the lower reaches of the Ishikari River. The committee members, comprised of esteemed professors, provided various opinions regarding the experimental results. However, at that time, I lacked responses beyond the experimental data, leaving me feeling quite frustrated. Particularly, I couldn’t answer basic questions like “Why is this part of the river bed getting deeper?” or “Why is sediment accumulating here?” as well as more specialized questions like “What’s happening with the similarity low?” or “Why do the riverbed forms differ between the experimental and real sites?” It was a painful realization of my own incompetence.

Such frustrations led to the idea of creating my own tools. I gathered various information, sought help from anyone worldwide, and tirelessly experimented day and night, regardless of weekends or holidays. Those days were not just about developing models; they encompassed various activities, including human exchanges domestically and internationally (which, in hindsight, might have been the most important). By chance, I was granted a one-year opportunity for study in the United States, where I had a fateful encounter with Dr. Jon Nelson of the USGS. This encounter laid the groundwork for the iRIC project, which we started together, and became the greatest event of my life.

Subsequently, over the course of more than 20 years, I developed models for river flow and bed morphodynamics. The next step was to develop a free software tool not just for my own use, but for anyone to easily experience river floods and meandering characteristics. This evolved into the internationally recognized iRIC project. iRIC aims not only to provide river computational models but also to enable users worldwide to create computational data, visualize results, and even animate them, all for free. Moreover, the word “Interface” in iRIC’s origin (International River Interface Corporative, named by Jon Nelson) underscores the importance of human interaction.

Through subsequent iRIC activities, the goal of disseminating models developed by researchers to a wide audience, including beginners, has to some extent been achieved. We have gained many users, and numerous applications have emerged. Considering my frustrating experience 40 years ago, it feels like an incredibly convenient era. However, there’s also been an increase in users treating the model as a black box, resulting in applications where the credibility of results isn’t always high. While the iRIC project can be considered successful from the perspective of making the model accessible, further efforts are needed from an educational standpoint to teach users numerical computational techniques beyond just using the model as a tool.

With this in mind, I have compiled this book, “Hydraulics for Practitioners Reiwa Era Edition”, explaining a two-dimensional river morphodynamics model similar to the one I developed in the past (iRIC-Nays2DH), including the theoretical background of governing equations and numerical analysis methods. All the source code mentioned in the text is publicly available on GitHub, some of which is compatible with iRIC, allowing readers to understand the model alongside the explanations. This book, labeled as the “Reiwa Edition,” is a continuation of the technical material titled “Hydraulics for Practitioners” which originated from materials presented at an in-house study group organized by Dr. Kiyoshi Hoshi, then the director of the CERI, during my tenure as a chief researcher there. It explains one-dimensional flow and bed deformation analysis in alluvial rivers, which I still believe to be useful today, but I have always wanted to create materials that reflect the evolution of models since then. This book is a culmination of that desire, covering the latest advancements in flow and riverbed morphodynamics analysis technology. I pride myself on its detailed explanations, believing it to be the most comprehensive resource available. Preventing the blackboxing of models is essential not only for nurturing individuals who can solve Japan’s river-related issues but also for enhancing international research and technological capabilities. If this book can contribute even slightly to such goals, it would bring me great joy.

Please note that this book is an English translation of the content already published on the Japanese website. While reading this text, I hope you can follow along and confirm the content by actually trying it out.

I would like to express my sincere gratitude to Dr. Chikako Yamamoto for her tremendous assistance in creating the English version.

April 13, 2024

Yasuyuki Shimizu