Managing Frozen Rivers
-Clarification of ice jams phenomenon and development of a discharge estimation
method-
 Example of the application of unmanned construction |
 Unmanned construction following the Mid Niigata Prefecture Earthquake in 2004 - Remotely controlled machine and an operator with the controller (Provided by the Hokuriku Regional Development Bureau) |
 Continuous river ice thickness measurement method (cross-sectional view of the river) * Measurement can be conducted safely as it is a non-contact method |
In rivers in severely cold areas, ice forms with the temperature drop in the winter. Such frozen rivers are problematic in terms of flood control and water utilization.
A problem related to flood control is ice jams. With the temperature rise
in spring, river ice melts and flows downstream. If this ice accumulates
and blocks meandering sections, ice jams occur and the decrease in the
water flow area causes a sudden rise in the water level. In the Teshio
River located in northern Hokkaido, ice jamming caused an increase in the
water level on Apr. 4th and 5th, 1961, resulting in damage to farm crops
and fertilizers. The status of river ice during thawing has not been fully
clarified as manual observation involves danger.
In terms of water utilization, there is a problem concerning the river water volume (flow discharge). Since droughty water-discharge (the minimum amount of discharge for 355 days a year) is often recorded when rivers are frozen, the freezing season is important for year-round water resource planning. In addition, since rivers in Hokkaido freeze for approximately 100 days a year from late December to early April, it is important to estimate the flow discharge in the freezing season accurately even if the winter discharge increases due to climate changes in the future. However, such an estimation method has not been established due to the lack of knowledge regarding the influence of river ice on flowing water.
The River Engineering Research Team conducted non-contact, continuous measurement of the river ice thickness on the Teshio River in the thawing season using a snow depth meter and an echo sounder to clarify the thawing phenomenon that causes ice jams. The observation results revealed that thawing occurs as snow turns to rain with the spring temperature rise; rain increases the river flow discharge and velocity, and the water flow melts the underside of the river ice. With regard to the discharge estimation method, detailed field observation was conducted and the observation data was analyzed. A method for estimating the flow discharge in the freezing season was developed with consideration to the phenomenon in which water flow changes the shape of river ice with the passage of time and causes changes in flowability. The accuracy of the estimation made with this method was found to be higher than that of conventional methods. Since there are a number of unique problems caused by river ice, it is important to promote comprehensive studies by reflecting the results of field observation, water channel experiments and numerical calculation to clarify the formation process and flow mechanism of river ice. Our team is conducting studies to contribute to the appropriate management of frozen rivers through the solution of these problems.
(Contact: River Engineering Research Team, CERI)
Studies to Restore Submerged Vegetation Zones
 Submerged vegetation growing in a test pond at PWRI |
 Hydrilla |
 Offshore breakwater in Lake Kasumigaura |
 Aerial photograph of the offshore breakwaters (Source: Google Earth) |
There are beautiful scenic views around Lake Kasumigaura, for example, extensive lotus fields and traditional sail boats called Hobikisen.
In only 30 years, the habitat environment has drastically changed due to population growth and development of the watershed.
The government has implemented a variety of measures to recover water quality, but it can not do so.
The River Restoration Research Team has conducted a study to restore the natural environment of Lake Kasumigaura, and in recent years, has in particular, been conducting a study to develop a method of restoring the submerged vegetation (a kind of waterweed).
Our previous researches have revealed that the restoration of submerged vegetation communities can contribute greatly to the improvement of lake environments in a variety of ways.
For example, submerged vegetation weakens the force of waves, preventing them from stirring up sludge accumulated on the lake bed, this action can be counted on to improve water quality by increasing transparency, and submerged vegetation provides hiding places for fish juveniles, resulting in an increase in fish resources.
Based on these findings, in 2010, we plan to conduct field experiments in Lake Kasumigaura to restore submerged vegetation.
To promote growth of submerged vegetation, the waves must be weak and there must be bottom sediment (sand on the lake bed) which is fine and easily penetrated by roots and enough sunlight for photosynthesis to occur.
The shallower the water, the greater the impact of waves, which means deeper water areas are more suitable for submerged vegetation and sunlight will not penetrate the deep water area because the present transparency in Lake Kasumigaura is low .
A field survey was performed considering these facts, and we established three study sites in Lake Kasumigaura where the wave strength, fineness of the bottom sediment, and the quantity of sunlight penetrating the water were in balance considering the state of construction of offshore breakwaters (offshore wave breaking structures installed in order to mitigate the impact of waves on breakwaters).
In these experimental sections, we plan to transplant submerged vegetation which was grown in Lake Kasumigaura according to past records. Then we will continuously monitor the vegetation to examine the appropriate restoration location and submerged weed species, and thereafter to develop effective methods of restoring the submerged vegetation.
This experiment is counted on to open the way to the eventual restoration of the past beauty of Lake Kasumigaura.
(Contact: River Restoration Research Team)
Challenge for More Efficient Unmanned Construction
- Research on technologies for remote operation of construction machinery
during disaster restoration -
 Example of the application of unmanned construction |
 Unmanned construction following the Mid Niigata Prefecture Earthquake in 2004 - Remotely controlled machine and an operator with the controller (Provided by the Hokuriku Regional Development Bureau) |
Recently, sediment disasters caused by guerrilla rainfall have occurred with increasing frequency. Unmanned construction has been undertaken to execute emergency countermeasure work immediately after these disasters in order to minimize the damage they cause, and full-scale restoration work performed after the damage has subsided to a certain degree.
Full-scale unmanned construction was performed as part of restoration work following the eruption of Mt. Unzen-Fugendake. Since then, this technology has been applied to execute restoration work following the eruption of Mt. Usu, and more recently, after the Iwate-Miyagi nairiku Earthquake in 2008, and to perform disaster restoration work in Minami-Osumicho in Kagoshima Prefecture. Unmanned construction has also been performed for maintenance in sediment check dam projects, to remove sediment etc. which has been temporarily stored by sediment check dams for example, and there are also cases where it has been used for permanent sedimentation prevention.
Remote operation of construction machinery used at such sites face problems. For example, their execution efficiency is lower than those operated by onboard operators, and they cannot be operated easily by anybody. So regardless of the high need for unmanned construction, individual judgments of its use are made according to the scale of each disaster and state of the site (degree of danger to humans), and its effectiveness must be enhanced by technological improvements.
This research is, therefore, intended to perform proving testing of operability, etc., to propose standard functions necessary for efficient remote operation using cognitive engineering etc., and to propose application technologies in order to broaden the utility and promote the wide use of remotely operated mechanized construction, based on remote operation technologies used for mechanical execution at Unzen-Fugendake and on technological systems which are the product of research and development based on the results of the Development of IT Execution Systems Based on Robots Etc., which is a comprehensive project of the MLIT (FY2005 to 2007) and on strategic research at the PWRI (measurement technologies, display technologies, excavation control technologies).
(Contact: Advanced Technology Research Team)