Title: River Development for Flood Control and Environment Conservation Using the Simple River Environmental Assessment Tool EvaTRiP

Introduction

  Small and medium-sized rivers occupy about 90% of the total length of rivers in Japan and play an important role in the conservation of the Japanese river environment. However, there are still various problems left unsolved in the environmental field after past river improvement projects. The majority of small and medium-sized rivers are managed by local governments, or prefectures, cities, towns, and villages. Those rivers have different characteristics from the larger rivers generally managed by the national government. For example, there are significant budgetary restrictions, the level of river development is generally lower than that of nationally managed rivers, and there are many cases where river maintenance is a burden for the local government. In addition, since those rivers are smaller in scale, river channel improvement tends to change the river environment or natural landscape significantly. The Aqua Restoration Research Center conducts R&D activities to provide solutions to those problems and to provide support for appropriate implementation of river channel improvement and river management.

Simple River Environment Assessment Tool EvaTRiP

  In many cases, river improvement of small and medium-sized rivers is conducted as part of post-disaster restoration projects. Among these, projects involving disaster rehabilitation, including river improvement, can be a good opportunity to improve the environment as they generally change the river channel shape significantly. On the other hand, since river channel plans often have to be developed in a very short time in such situations, environmental consideration may take place later than necessary. In addition, when quantitative review of a river plan is performed, it mainly depends on the assessment of the flow capability based on one-dimensional non-uniform flow calculation, and environmental aspects, such as the quality of the habitat, are not assessed (Figure 1). To create a river with multiple natural features even within disaster rehabilitation projects, we need a tool that can assess a project both in terms of flood control and environmental conservation swiftly and quantitatively and support river channel planning.

  In response to this need, the Aqua Restoration Research Center developed a simple environmental assessment tool EvaTRiP (Evaluation Tools for River environmental Planning). Working as a part (the solver) of the functions of free riverbed change calculation software iRIC, EvaTRiP imports the results of changing water depth and flow speed data obtained by riverbed change calculation and calculates assessment values related to the environment. To be specific, it outputs possibility of plant growth in the river channel and calculation results of the habitat suitability for fish based on existing knowledge. As the results are related to environmental conservation of the river bank, the tool also judges the necessity of revetments or evaluates the stability of riverbed materials.

  Fig. 2 shows an example of field application. Fig. 2(a) shows two adjacent improved sections of the same river, one with a straightened channel and the other a channel with expanded width. Riverbed change calculation conducted for these two sections gives the distribution of tractive force in Fig. 2(b), and assessment with EvaTRiP gives a potential of habitat suitability of the adult pale chub in Fig. 2(c). Based on these results, it is visually confirmed that the tractive force is greater in the entire area of the straight section than in the widened section and that the habitat suitability is also lower in the former than the latter. As explained above, the tool can immediately convert the calculation results into the assessment values. Using this tool, we are achieving simple and quantitative evaluation of river channel change from both the flood control and environmental aspects.

Toward the Establishment of a New River Channel Design Process

  In practical application, the river channel design process should involve the evaluation of river channel topography every time the topography changes for the ultimate purpose of determining the optimal shape. To this end, we are also currently developing a tool capable of freely editing the river channel topography (RiTER in Fig. 1). We believe these new techniques will be able to accelerate the introduction of CIM (construction information modeling) in rivers. The Aqua Restoration Research Center intends to establish a new river channel planning and design procedure using the comprehensive tool explained here so as to help promote the creation of small and medium-sized rivers with multiple natural features.

(Contact: Aqua Restoration Research Center)

A Study on the Advanced Use of the Groundwater Level Control System in Large-Scale Rice Paddy Fields

  With one-fourth of its land used for farming, Hokkaido Prefecture is the largest food supplier in Japan. However, as the number of farmers has been decreasing, the consolidation of farmland for core farmers and the implementation of highly productive agriculture are urgent issues. In large-scale rice paddy fields, the expansion of the fields and the installation of a groundwater level control system (Figure 1) are promoted. This system has an underdrainage function, which swiftly drains excess water that is unnecessary for the growth of crops through an underground drainage pipe buried in the field. The underground drainage pipe can be cleaned by injecting water into it. Moreover, this system is also capable of underground irrigation; that is, it can supply necessary water to the crops from underground.

  Underground irrigation is effective for water management after direct seeding of rice and for affusion to rotation crops during a drought. For example, with dry direct seeding, the more stable growth of seedlings can be achieved by moisturizing the surface soil by underground irrigation. In addition, underground irrigation is also effective for the stable growth of soybeans, especially in case of a drought, from the flowering stage to the pod development stage, in which a large amount of water is needed. However, in order to conduct effective underground irrigation, water needs to be supplied and drained swiftly and uniformly across the entire field. This study aims to investigate changes and dispersions in the groundwater level during underground irrigation in actual fields, reveal their relationships with the condition of the soil in the field, and seek measures to prevent uneven water supply or drainage.

  So far, we have measured changes in the groundwater level during underground irrigation in large-scale rice paddy fields with peat subsoil in middle and southern Hokkaido. In some cases, the groundwater level rose, but water supply or drainage was uneven across the field. In other cases, the groundwater level did not change between before and after underground irrigation (Figure 2). The factors that contributed to these results were considered to include differences in the water permeability and drainage property of the soil within and among the fields. In promoting the expansion of farm fields, fields that were used for different crops, such as those used for rice and those used for other field products, may be consolidated into one field. In addition, the soil and its property vary from region to region. Our team will work on the clarification of the relationship among different field conditions, including unevenness in water supply and drainage and soil properties, while also examining the effect of subsoil breaking.

(Contact: Rural Resources Conservation Research Team, CERI)

Tasks and Technical Development of Shallow Undergrounding of Utility Lines in Cold Region
~Freezing Experiment on Water Inside Optical Cable Pipelines~

Introduction

  In Japan, elimination of overhead power lines and electric poles has been required to help boost tourism, improve landscapes, and prepare for disasters. However, it is pointed out that those undergrounding of utility lines in Japan has lagged far behind the US, Europe and parts of Asia. It was mainly caused by high initial costs and lowly efficient compared with overhead lines.

  Shallow undergrounding is one of the low-cost techniques. Therefore, the Ministry of Land, Infrastructure, Transport and Tourism(MLIT) established the Technical Investigation Committee for Shallow Undergrounding in September 2014. The standard was relaxed so as to allow the installing of utility cables more shallowly than before in April 2016.

  While, in cold regions such as Hokkaido prefecture, Japan, utility pipelines and cables are installed deeper than the frost penetration depth to protect against malfunctions by freezing of stagnant water in underground pipelines and frost heaving. Therefore, the relaxed regulation has not been applied in Hokkaido. It has not been clarified whether the undergrounding of utility lines at depths shallower than the frost penetration depth causes problems, and if so, what factors underlie these problems. It is possible to say that the safety against malfunctions has been overestimated.

  We conducted an outdoor exposure experiment using stagnant water and specimens that reproduced curved pipelines. We clarify the mechanism of freezing for stagnant water in underground pipes and the influence of such freezing on optical cables. Based on the results, local government conducted shallow undergrounding work in actual road.

Outline of the research

  One problem is the freezing of stagnant water in pipelines. This problem is crucial particularly for communication cables, which do not generate heat, unlike power cables.The stagnant water in pipelines expands when it freezes and may cause functionality of the communication cables to deteriorate.

  First of all, we conducted the indoor experiment of freezing stagnant water in optical-cable pipes. The specimens were 1m-long closed pipes that contained optical cables and water. Optical cable of 200 scale is used in specimens assuming the telecommunication using the urban area. To reproduce the conditions of stagnant water in the pipeline, two patterns of specimen were prepared. One was fully filled with water and the other was half filled with water. In this experiment, communication functionality deterioration or cable disconnection did not occur under either condition.

  Following the indoor experiment, an outdoor exposure experiment was done using stagnant water and specimens that reproduced curved pipelines. Specimens of the experiment are shown as Fig.2. The lengths of the specimens are 10m plus rising double-end. Test section 1 is straight portions which are filled with water. Test section 2 is 3m with 2 concaved places which are filled with water and half-filled with water. And transparent VU piping 100phi was used to visualize the inside freezing situation. We observed the attenuation in communication volume and the state of water inside pipes for 6 day consecutively.

  The outdoor air temperature was below zero throughout the experiment. As a result, the stagnant water in Specimens 1 and 2 was observed to freeze through twice, and a 10% expansion in volume in the direction of the axis of the pipeline was observed during the experiment. For both Specimens 1 and 2, the communication attenuation was sufficiently smaller than the optical fiber loss standard value throughout the period of the experiment.

  In light of this, we verified that the freezing of the stagnant water in the pipeline did not affect communication functionality under the conditions of the experiment. Based on the above experiment results, it is feasible to employ shallow layer undergrounding in cold regions, because it is thought that considerable compression and extension do not affect the optical cables under the condition where there are open spaces for the water to move in the pipeline even when part of the water freezes.

  Based on the results, Chitose city introduced shallow undergrounding work into update construction project for underground cables of municipal water facility. The utility cables and pipelines were installed in 60cm underground compared with usual standard 120cm.(Fig. 3 and Fig.4) The reduction in the depth of undergrounding results in a substantial decrease in the need for excavation and back-filling work, and thus costs and work period were curtailed. From now on, the investigation of the freezing situation in construction fields will be performed to verify conditions in which the shallow underground burial in the cold district succeeds.

(Contact: Scenic Landscape Research Team, CERI)