1:45 PM - 3:15 PM
[O08-P26] Modeling of backwater phenomenon between Hirase River and Tama River and ideas for disaster mitigation
Keywords:backwater phenomenon, the rise in water level, the mainstream, the sub stream
1. Introduction
In recent years, rivers have been flooding frequently due to heavy rain. We found that one of the factors was the backwater phenomenon. This phenomenon occurs when water from tributaries is unable to flow into the mainstream, causing flooding a little upstream from the confluence of the tributaries (Figure 1). Therefore, it would be possible to prevent river flooding by implementing measures inside the river other than levees. We modeled rivers where backwater phenomena occur, and conducted research to find ways to prevent flooding by modifying the interior of river confluences.
2.For the experiment
We created a model in which the backwater phenomenon occurs and conducted experiments using that model. The model was created with reference to the Tama River (mainstream) and Hirase River (tributary) (Figure. 2).
3. Experiment 1
(1) Purpose
The outline of the model was made of milk cartons, and the riverbed was made of plastic cardboard. And the milk carton and plastic cardboard were fastened with duct tape (Fig. 3). In order to make it easier to grasp the flow of the mainstream and the sub stream and the amount of overflow due to flooding, we conducted an experiment using BB bullets instead of water.
(2) Results, Discussions, and Issues
Ten silver BB bullets overflowed from the confluence. However, since the silver BB bullets stuck in the sub stream did not start flowing even after the BB bullets o mainstream had flowed out, it was found that the flow of the BB bullets in the sub stream was hindered not by the influence of the BB bullets of mainstream.
4. Experiment 2
(1) Purpose
The number of BB bullets and sub stream were used as they were in Experiment 1, and the smooth desks in the physics classroom were used for the main stream. The width of the main river was narrowed to 35 cm (Fig. 4).
(2) Results, Discussions, and Issues
Under these conditions, BB bullets from the sub stream were clogged at the confluence and did not flow into the mainstream, causing BB bullets to overflow in the upstream of the sub stream.
5. Experiment 3
(1) Purpose
We will check whether the backwater phenomenon occurs in the model using water and confirm the reproducibility. The amount of water is slightly reduced due to water leakage from the contact patch between the acrylic plate and the water tank when storing water (Fig. 5).
(2) Results, Discussions, and Issues
In addition, the water level at the confluence of the sub stream and the mainstream increased at one time compared to the other parts. It was confirmed that the backwater phenomenon occurs under these conditions (Fig. 6).
6. Experiment 4
(1) Purpose
Using a model using water, we will discover a method that prevents water from flowing back at the confluence of the sub stream.The height of the partition was made higher than the depth of the river, and it was made with a milk carton(Fig. 7). (The angle parallel to the tributary is 0ﾟ, and the clockwise direction is positive.)
1. Straight shape with a length of 7 cm and an angle of 0ﾟ
2. Straight shape with a length of 7 cm and an angle of 30ﾟ
3. 21 cm long and angled 7 cm from sub stream side
(2) Results, Discussions, and Issue
In both cases, it was confirmed that the water level of the mainstream had risen, leading to the result that a considerable amount of water that should not have overflowed in partition 1 and partition 3. Of the three partitions, partition 2 is the most useful for mitigating backwater phenomena and can prevent flooding of the mainstream.
7. Prospects
By improving the way, the water flows in the mainstream, we will increase the time it takes for the water level to rise at the confluence and produce a model with a higher reproducibility of the backwater phenomenon. The purpose is to model a system that prevents backwater phenomena and prevents flooding.
In recent years, rivers have been flooding frequently due to heavy rain. We found that one of the factors was the backwater phenomenon. This phenomenon occurs when water from tributaries is unable to flow into the mainstream, causing flooding a little upstream from the confluence of the tributaries (Figure 1). Therefore, it would be possible to prevent river flooding by implementing measures inside the river other than levees. We modeled rivers where backwater phenomena occur, and conducted research to find ways to prevent flooding by modifying the interior of river confluences.
2.For the experiment
We created a model in which the backwater phenomenon occurs and conducted experiments using that model. The model was created with reference to the Tama River (mainstream) and Hirase River (tributary) (Figure. 2).
3. Experiment 1
(1) Purpose
The outline of the model was made of milk cartons, and the riverbed was made of plastic cardboard. And the milk carton and plastic cardboard were fastened with duct tape (Fig. 3). In order to make it easier to grasp the flow of the mainstream and the sub stream and the amount of overflow due to flooding, we conducted an experiment using BB bullets instead of water.
(2) Results, Discussions, and Issues
Ten silver BB bullets overflowed from the confluence. However, since the silver BB bullets stuck in the sub stream did not start flowing even after the BB bullets o mainstream had flowed out, it was found that the flow of the BB bullets in the sub stream was hindered not by the influence of the BB bullets of mainstream.
4. Experiment 2
(1) Purpose
The number of BB bullets and sub stream were used as they were in Experiment 1, and the smooth desks in the physics classroom were used for the main stream. The width of the main river was narrowed to 35 cm (Fig. 4).
(2) Results, Discussions, and Issues
Under these conditions, BB bullets from the sub stream were clogged at the confluence and did not flow into the mainstream, causing BB bullets to overflow in the upstream of the sub stream.
5. Experiment 3
(1) Purpose
We will check whether the backwater phenomenon occurs in the model using water and confirm the reproducibility. The amount of water is slightly reduced due to water leakage from the contact patch between the acrylic plate and the water tank when storing water (Fig. 5).
(2) Results, Discussions, and Issues
In addition, the water level at the confluence of the sub stream and the mainstream increased at one time compared to the other parts. It was confirmed that the backwater phenomenon occurs under these conditions (Fig. 6).
6. Experiment 4
(1) Purpose
Using a model using water, we will discover a method that prevents water from flowing back at the confluence of the sub stream.The height of the partition was made higher than the depth of the river, and it was made with a milk carton(Fig. 7). (The angle parallel to the tributary is 0ﾟ, and the clockwise direction is positive.)
1. Straight shape with a length of 7 cm and an angle of 0ﾟ
2. Straight shape with a length of 7 cm and an angle of 30ﾟ
3. 21 cm long and angled 7 cm from sub stream side
(2) Results, Discussions, and Issue
In both cases, it was confirmed that the water level of the mainstream had risen, leading to the result that a considerable amount of water that should not have overflowed in partition 1 and partition 3. Of the three partitions, partition 2 is the most useful for mitigating backwater phenomena and can prevent flooding of the mainstream.
7. Prospects
By improving the way, the water flows in the mainstream, we will increase the time it takes for the water level to rise at the confluence and produce a model with a higher reproducibility of the backwater phenomenon. The purpose is to model a system that prevents backwater phenomena and prevents flooding.