Tidal amplitude and coast economy – Eng. Doan Manh Dung

Tidal amplitude and coast economy – Eng. Doan Manh Dung

Tidal amplitude affects seaport planning, flood control and coastal habitats.

1.Formula for calculating the output through an open channel

2.Sedi formula when B>>>h

In flood or tide, the width B of the stream is infinitely large compared to the depth h.


3. Relationship between sea high level and tidal amplitude.

At a point on the coast with a tidal range, the sea level elevation there is the average of all tidal amplitudes at that point.

4. Consequences

With the definition of “Sea level elevation” in section “3.” the place with the highest tidal range will be the place where there are periods of existence with the lowest water level compared to neighboring locations. From formula (5), we determine that: The river from inland will tend to move towards the coast with the highest tidal amplitude in the area.

5. Applications

5.1 “The direction of the river when flowing into the sea” is common phenomenon on earth, but it is not evident clear at the countries having few rivers or in islands.

Vietnam is a narrow and long land, with many rivers, so the phenomenon of “Directing the river flows to the sea” has been studied by KS Doan Manh Dung since the late 1990s in the process of studying to deal the flood from Mekong Delta to Thailand bay. The results of this study were introduced in proceedings in 18th Conference of ASEAN federation of engineering Cooperation at Hanoi- Vietnam on 24th Dec.2000 with article named “What solution to the Hoa Duan  isthus”  In countries formed by many large and small islands or with few rivers, the phenomenon of “direction of flow to the sea” is not clear, so it is rarely studied.

5.2 Avoid building ports at the location – where the river exits to the sea.Seaports should not be built where there is a high amplitude of the water field and where alluvial sources are heading.

Example 1: The tidal amplitude from Thang Binh – Quang Nam increases gradually to Ky Ha port – Quang Nam. Therefore, the Truong Giang river in Quang Nam province runs along the coast, it is difficult to escape to the sea. It must flow to Ky Ha port to the sea. Therefore, it is not possible to build Ky Ha port  as a deep-water port.

Example 2: The tidal amplitude at Hon Dau – Hai Phong on June 5th, 2007 is 3.7 m, at Hon Gai – Quang Ninh is 4.0 m and at Cua Ong – Quang Ninh is 4.5 m. Therefore, the mouth of the Cam River tends to bring alluvium to the northern waters. That is the reason alluvial is accreting at Lach Huyen port.

5.3 Determination of flood outlet from the Mekong Delta to the Gulf of Thailand.When transferring floods from the Long Xuyen Quadrangle to the Gulf of Thailand, flood must exit at Rach Gia. Because the tidal amplitude is 0.9 m from Ha Tien and gradually increases to Rach Gia 1.8 m. At Hon Dat, the tidal amplitude is about 0.9 m. Therefore T5 canal at Hon Dat, flood is difficult to escape to the sea and it destroy the road No 80th from Hon Dat to Rach Gia.

5.4 Locating a flood outlet for a coastal city

When a coastal city like Bangkok, the west has a tidal amplitude is 50 cm higher than the east, so Bangkok city should drain the main flood to the west.

5.5 Determine the instability of pH in Tam Giang lagoon and propose to organize a type of scientific tourism on natural geography.

In Thua Thien – Hue, the tidal amplitude is high at the two ends of Thuan An and Tu Hien estuaries. The above amplitude gradually decreases in the coastal area between Thuan An and Tu Hien.Because this land is strongly alluvial from the sea direction, both Thuan An and Tu Hien estuaries are often filled up. This area is located in an area with many storms and floods. The flood season has raised the water of Tam Giang lagoon and in history has broken Hoa Duan dam many times. The natural process when floods break the dam to open the sea mouth, to the sedimentation from the sea, the water in the integrated dam due to storms and floods … has changed the pH according to the cycle of many years in Tam Giang lagoon waters.This is one of the reasons why farmers and fishermen in Hue have many difficulties.

In order to develop agriculture and fisheries in Thua Thien – Hue, it is necessary to carefully study the above phenomenon and have a solution.A position with a tidal amplitude of 0, rare in the world. Should add a form of tourism to learn about natural geography to enrich tourism services.