Minis Agri and Rural

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ministry of agriculture and rural development of vietnam institute of water resources planning flood control planning for red river basin Hanoi 9 - 2001 BY : PH.D TO TRUNG NGHIA ME. VU HONG CHAU

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ministry of agriculture and rural development of vietnam institute of water resources planning flood control planning for red river basin Hanoi 9 - 2001

Presentation topics: 

I: Introduction II: River system of Red river basin III: The formation of Red river flood IV: Economic and Infrastructural development V: Flood control solutions VI: Implementation plans for solutions Conclusion Presentation topics

I. introduction : 

Red river and Thai Binh river basin are located at latitude 200 - 250 30' North, longitude 100 - 1070 10' East in tropical monsoon zone. The total area of the two basins is 169,020 km2, in which 86,720 km2 belongs to Vietnam, accounting for 51% of the total area, and 82,300 km2 lie in Chinese territory, making up 49% of the total area (the remaining 1080 km2 is located in Lao PDR). The total area of Red and Thai Binh river basins can be divided into 4 main sub- areas which include : Upstream and midland of Red river to Son Tay : 143,700 km2 Upstream and midland of Thai Binh river to Pha Lai :12,680km2 Tich, Boi and Hoang Long river basin : 2,800 km2 Downstream of Red and Thai Binh river : 9,840 km2 I. introduction

II. River system of Red river basin: 

II. River system of Red river basin Upstream and midland of Red river system : Having an area of 143,700 km2, 82,300 km2 out of which belong to China and Lao PDR, accounting for 57% and the remaining 61,400 km2 is located in territory of Vietnam making up 43% of the total. Consisting of 3 basins of great water storage as Da, Thao and Lo rivers. Upstream and midland of Thai Binh river system : The entire area of 12,680 km2 ending up in Pha Lai is located in the territory of Vietnam Consisting of 3 basins of great water storage as Cau with a area of 6,030 km2 equaling to 48%, Thuong river 3,580 km2 translating to 28% and Luc Nam river 3.070 km2 making up 24% of the total.

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River system of the delta : The right bank of Red river having an area of 4,166 km2 consist of major tributaries as Day, Nam Dinh, Ninh Co rivers. The left bank of Red river lie between the main flow of Red river and Thai Binh river have an area of 3,851 km2, constituting a large delta run through by tributaries of Duong, Luoc and Tra Ly rivers. Thai Binh river downstream : The area contain many tributaries. From the Pha Lai junction, the main flow is divided into two flood drain directions : one towards Kinh Thay river and the other drains into main flow of Thai Binh river through Cat Khe to the sea. The flood flow of Red and Thai Binh river from upstream run to the Red river delta, taking the tributaries before pouring into the sea through 9 estuaries : Day drain 19,1%; Ninh Co 5,7%; Ba Lat 21,2%; Tra Ly 8,9%; Thai Binh 6,1%; Van Uc 19,2%; Lach Tray 4,7%; Nam Trieu 10,3% and Da Bach 4,8%.

III.1 The formation of Red river flood: 

III.1 The formation of Red river flood Recorded data indicater that the floods in northern delta are formed mainly form the flood in Red river basin, accounting for 80 - 85%, and in Thai Binh river basin, making up 10 - 15% and in Tich and Boi river basins, equaling to 2 - 4%. Floods in Red river include ones from Da river, constituting 37 - 69%, Lo river 17 - 41,5% and Thao river 13 - 30% (in peaks discharge). The big floods in the Red river often occur during the mid of August. During these times, the flood in which water levels equal to or even exceed the design water levels of 13.6m in Hanoi which are caused by the great floods of 2 or 3 rivers. The process is as follows :

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Flood in August 1971 resulted in a water level of 14.82 m in Hanoi, in which the peak discharge reach 37,800 m3/s in Son Tay caused by the first biggest flood of Lo river confronting second largest flood of Thao river and the fourth one of Da river. Flood in August 1945 raised water level to 14.43 m in Hanoi, the peak discharge of 34,250 m3/s in Son Tay is the combination of second largest flood of Da river confronting third largest flood of Thao river and the seventh one of Lo river Flood in August 1969 raised water level to 13.66 m in Hanoi, the peak discharge of 28,900 m3/s in Son Tay is caused by fifth big flood of Da river, sixth big flood of Lo river and medium flood of Thao river.

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Flood in August 1996 in Hanoi with water level of 13.46 m and the peak discharge in Son Tay reaching 27,200 m3/s was due to the combination of first biggest flood of Da river and the tenth biggest flood in Lo and Thao rivers. Floods in Red river have been appearing at the increasing rate. Three out of four record largest floods of 20th century occurred within a period of 30 years from 1969 - 1999 in Red river basin. The flood in August 1996 in Da river is the ever largest flood in 20th century with peak discharge measured in Hoa Binh of 22,600 m3/s ( August 1971 flood having Qmax = 16.200 m3/s, one in August 1945 Qmax = 21,000 m3/s and the last in August 1969 reaching Qmax = 15,800 m3/s ).

III.2 The formation of Thai Binh river flood: 

III.2 The formation of Thai Binh river flood The upstream Thai Binh flood flowing into Pha Lai is formed from 3 rivers of Cau, Thuong and Luc Nam. According to available statistics, there are 22 big floods above the 3rd warning water level took place in Pha Lai in the period of 1960 - 1990, in which 43.5% came from Luc Nam river, 34.3% from Cau river and 22.2% from Thuong river. Flood of Red river overflowing into Pha Lai through Duong river make up 69.9% of the total flood flow in Pha Lai. The major floods in Thai Binh river are listed as follows : August 1937 with total volume of 3 rivers of 7,130 m3/s July 1986 with total volume of 3 rivers of 7,992 m3/s August 1968 with total volume of 6,800 m3/s August 1995 with total volume of 4,000 m3/s

IV. Economic development and infrastructure construction: 

IV. Economic development and infrastructure construction infrastructural system of Hong - Thai Binh river delta Flood plain and midland of Hong - Thai Binh rivers are socio-economic centers of the country which include the entire territories of 10 provinces and part of Phu Tho, Vinh Phuc, Thai Nguyen, Bac Giang, Quang Ninh provinces. Total area protected by the dyke system is 14,425 km2 , in which agricultural area is 879,285 ha, forestry 79,719 ha, aquaculture 73,190 ha (according to 1997 statistics, there are 38 flood effected areas).

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Due to the fact that the ground elevations of flood plain and midland of Hong and Thai Binh rivers are so low that during the flood season, the entire delta and its infrastructure system obtain lower level than that of river flood from 3 - 5 m. This level is 5 - 7 m lower than the highest level during the flood in August 1971. The river is seen as a suspension river, representing a threat once dyke collapse confront the flood plain. Flood is considered as one of the great risk to lives and properties of a population of 17.7 millions residing in the delta, infrastructure and real assess worth 52.84 billions USD and a GDP of 4.2 billions USD (1977).

Criteria for flood control of downstream area (planning phase1972 - 1990): 

Criteria for flood control of downstream area (planning phase1972 - 1990) Capable to be protected against flood in August 1971 which had peak discharge in Son Tay of 37,800 m3/s and water level in Hanoi of 14.82 m

V. Flood control solutions for flood plain and midland of Hong - Thai Binh rivers: 

V. Flood control solutions for flood plain and midland of Hong - Thai Binh rivers Strengthening of the river dyke systems Increase the flood drain capacity of the river system. Flood detention and diversion zone. Upstream reservoir contruction for flood protection. Growth and protection of watershed. Effective management and exploitation of flood control solutions. Map of red river basin

VI. Emplementation plant for solutions : 

The analysis comprised the period 1902 - 1998 in Son Tay - largest flood flow with return period occurrence : 100 year Qmax = 37,600 m3/s 200 year Qmax = 41,300 - 41,500 m3/s 250 year Qmax = 42,000 - 42,600 m3/s 300 year Qmax = 44,200 - 45,000 m3/s 500 year Qmax = 48,000 - 48,500 m3/s 1000 year Qmax = 51,000 - 51,700 m3/s Regarding the August 1971 flood with highest flow of 37,800 m3/s in Son Tay, recalculation showed a flood frequency P = 0.8% and a return period of 125 years. VI. Emplementation plant for solutions

Solution 1 : Red river dyke system: 

Solution 1 : Red river dyke system Dyke is seen as a traditional and basic solution of flood plain and midland of Red river in the immediate time and in the long term. The existing dyke system of flood plain and midland of Hong and Thai Binh rivers have been constructed from the 6th and 7th century and have been being upgraded in terms of design flood water levels and dyke elevation in Hanoi in the following years : YEAR W.L DYKE ELEVATION 1915 : 10.70 m 11.2 m 1920 : 11.00 m 11.5 m 1923 : 11.50 m 12.0 m 1932 : 12.00 m 13.3 m 1960 : 13.00 m 14.3 m 1963 : 13.30 m 14.6 m 1977-1996 : 13.60 m 15.1 m ( Basing on Water resources datum system as of 10,800 m )

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1. Design flood water level Circular No. 1185 dated July 1977 (former Water Resource Ministry) stipulated the design flood water level of dyke system of Hong and Thai Binh rivers. The design flood water level in Hanoi is 13.6 m and 7.0m in Pha Lai 2. Existing condition of river dyke elevation So far, all of the 45 main river dykes in Red and Thai Binh river with total length of 2,300 km have had top dyke elevations capable of controlling against overtopping of designed flood levels. However, the incremental elevations at some sections are not satisfied, some are downstream dyke, estuary dyke and some dyke sections at the end of Hong, Duong, Luoc and Thai Binh rivers.

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3. Dyke cross section Dyke surface, slope, berm, foot, foundation have not met the technical requirements. At present, 200 irrigation sluices under dykes are not safe enough during flood season due to following reasons : the flood level is already higher than design water level of the irrigation sluices which has been in use for 50 - 70 years and in urgent need of new construction or improvement. Distances between the two major dykes are not uniform, some are too long while the other so narrow, some reaching the river bank

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After Red river dyke, Duong river dyke is a critical dyke. The distance between the two dykes are narrow, representing 15 sections under the threaten conditions. The height of 45 river dykes are the utmost limit. The more the dykes are raised, the less dyke safety is ensured. So the design water level of dyke could not be raised any longer. In the immediate time and in the long term, great effort should be made to improve the dyke surface regarding dyke design standards, upgrading and newly construction of obsolete or damaged sluices under dyke.

Solution 2 : Increase the drainage capacity of the river system: 

Solution 2 : Increase the drainage capacity of the river system Dredging the river to increase the flood drain capacity and lowering the flood water level are the traditional solutions which have been applied in the flood plain and midland of Red river since 11th century. According to analysis result, during the period 1930 - 1990 (60 years) with the same flow of 20,000 m3/s in Son Tay, the water level rose by 1.3 m and with the same flow of 14,000 m3/s in Ha Noi, the water level rose by 1.06 m. Only from 1970 to 1996 (26 years) with the same flow of 29,000 m3/s in Son Tay, the water level in Ha Noi rose by 0.6 m (from 13.3 m to 13.9 m).

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The reason for the increased water level is due to the silt filling of river bed and bank, the encroachment of river bank and particularly the sub dyke narrowing the flow and flood way. The distances between the two main dykes are so near in some places : Lien Mac 1600 m, Chem 1200 m, Thang Long bridge 1650 m and Chuong Duong 1200 m. Solutions of emptying the river bed and removing of sub-dyke have been proposed many times but failed to be realized. On the other hand, the encroachment of river bed and bank are increasing as sub-dyke elevation to be raised to an level above warning level III.

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For bars having area of more than 1000 ha and accommodating ten of thousands of people as on the left of Red river : Vinh Tuong, Yen Lac, Yen Lang, Tu Dan, Khoai Chau, Phu Hung Cuong, Tan Lap, Duy Nhat.. and on the right of Red river : Phu Chau, Trung Chau, Tu Lien, Nhat Trung... The total residents of 53 bars in Red river to be resettled will amount to 249,775 people with total area in the bars of 26,686 ha (1995). The total property value is estimated at 380 million USD and a GDP earned is 61.6 million USD Such bars in Duong, Thai Binh, Luoc and Dao river have not been taken into account. So the removal of these bars, either entirely or partly, will present a low feasibility and cost a large expenditure.

Solution 3 : Day river flood diversion and flood retention zone: 

Solution 3 : Day river flood diversion and flood retention zone 1. Day river flood diversion From the completion of Day spillway, floods have been officially diverted into Day river twice since 1937 up to now : flood in August 1945 with flow of 1,950 m3/s and water level in Ha Noi get 12.66 m and flood in August 1971 with flow of 2,435 m3/s as water level in Ha Noi reach 14.13 m. Following August 1971 flood, the Day dam has been improved to raise the flood diversion flow through spillway to 5.000 m3/s. The deteriorated river and tightened flood storage area have resulted in a fact that only 3.200 m3/s is diverted for a water level of 13.4 m and 3,500 m3/s for 14 m in Ha Noi.

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2. Flood detention solution In 1999, the Government restored the flood storage areas in Red river which include Tam Thanh, Luong Phu, Quang Oai, and Lap Thach. However, the actual flood detention and diversion situation is as follows : The flood diversion flow into Day river did not exceed 3000 to 3200 m3/s and the total flood diversion volume obtained is 0.8 - 1 billion m3. Flood detention in the 4 areas not exceeding Qmax = 4000 - 5000 m3/s, with a capacity of 1 billion m3. Timely operation will reduce the water level in Ha Noi by 0.3 - 0.4 m. Sooner or later operation will cause the flood storage to be invalid as what had happened to the August 1971 flood.

3. The damaging rate suffered in the Day river flood diversion and flood retention zone : 

Day river flood diversion will have direct impacts on 675,000 people in provinces of Ha Tay, Ha Nam and Nam Dinh and inundate 41,235 ha of agricultural land, especially 2 districts of Chuong My and My Duc will be flooded 4 - 5 m under the water level during a period of 35 - 45 days together with 25,000 ha of agricultural land The total real properties of the entire area are estimated at 13,556 billion VND (1997) and GDP earned is 1171 billion VND in which the total damage cost 3296 billion VND 3. The damaging rate suffered in the Day river flood diversion and flood retention zone

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The flood retention into 4 areas will cause direct impacts on 230,000 people and an area of 15,800 ha of agricultural land. The total real assess are valued at 9,365 billion VND (1997) and GDP earned is 812 billion VND in which the total damages are estimated at 2233 billion VND. Therefore, the flood retention and Day diversion should be seen as temporary and supporting solutions once the flood water level in Ha Noi exceed the elevation of 13.6 m. Untimely flood retention and diversion not only bring about less effects but result in more losses for people and social properties.

Solution 4 : Upstream reservoir contruction for flood protection: 

Solution 4 : Upstream reservoir contruction for flood protection 1 Recommends on reservoirs in planning report There are two recommendations for Da river : Low option : Lai Chau 295 m + Son La 215 m + Hoa Binh 115 m High option : Son La 265 m + Hoa Binh 115 m Dai Thi reservoir is recommended for Gam river 2. Hoa Binh reservoir in Da river and flood control task In the feasibility and in the technical design of Hoa Binh reservoir, the number one task of the reservoir is to control flood for the dowstream. Hoa Binh reservoir is to cutting flood to keep the water level in Ha Noi from exceeding 13.30 in the event of any flood of equal scope as the one in August 1971 under different forms.

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Hoa Binh reservoir is designed basing on following parameters : Istalled capacity 1960 MW High water level 120 m Entire capacity (to elevation of 115 m) 9.45 billion m3 Flood regulation storage (85 -115 m) 4.90 billion m3 The flood control period of Hoa Binh is divided into 3 phases : Flood at the beginning of the flood season 15th June - 15th July, main season from 16th July - 25th August and at the end of the flood season 26th August - 15th September.

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3. Thac Ba reservoir and flood control tasks Thac Ba reservoir in Chay river was designed in 1960 when the Water resources planning and exploitation of Red river system are not available, so the reservoir has been assigned with flood control tasks. Following its construction and initial operation, the reservoir has been assigned with additional responsibility of controlling downstream flood with a flood reguration storage of 450 million m3 The 10 year operation record for the period of 1990 -1999 show a fact that although the reservoir did not reserve a flood preventive flow of 450 million m3 as stipulated, by the end of flood season the reservoir has not stored as fully as required and fail to provide sufficient water for the hydroelectric generation in the dry season for 5 consecutive years (making up 50%)

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4. Downstream flood reduction effect of Hoa Binh and Thac Ba reservoirs : Since its operation in 1989, Hoa Binh reservoir in Da river and Thac Ba have carried out the task of cutting dowstream flood. In the possible events of large floods as the ones in 1945, 1969, 1971 and 1996. The water level in Ha Noi can quite be kept under 13.60 m and not exceeding 7.30 m in Pha Lai. So if any flood in Red river not as large as one in August 1971 may occur, Hoa Binh and Thac Ba reservoirs will cut the downstream flood together to maintain the flood water level in Ha Noi less than or equal to 13.0 m. We do not have to resort to the flood diversion of Day river and other flood retetion areas for the present time.

5. With resevoirs in both Da and Lo river: 

5. With resevoirs in both Da and Lo river Flood control capacity of 10 billion m3 in Da river and 1.0 billion m3 in Lo river : For 200 year : Water level in Ha Noi can be kept to 12.12 m. For 300 year : Water level in Ha Noi can be kept to 12.69 m. For 500 year : Water level in Ha Noi can be kept to 13.14 m. For 1000 year : Water level in Ha Noi can be kept to 13.48 m.

solution 5 : watershed growth and protection : 

solution 5 : watershed growth and protection Watershed growth and protection is such a traditional method to conserve land and water, avoiding erosion and exhaustion, the occurrence of flash, especially in the areas where reservoirs are not available, the midzone and Thai Binh basin. In 1960, Red river basin has 3.6 million ha of wood, making up 42% of the total basin area. In 1987 only 2.66 million ha left, equaling to 31%. Desert land accounts for 5 million ha, translating to 58% of the total.

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According to recent statistics of Forest Investigation and Planing Institute, the North-East natural land area the is 6.748 million ha in which forested area make up 2.368 million ha (both natural and planted). The North-West natural land area constitute 3.572 million ha in which forested area make up 1 million ha. The existing forested coverage of the two areas are estimated at 35.11% for North-East area and 26.97 % for North-West area. The proposed plan relating the forest soil in the 5 million ha program up to the year 2010 will cover North-East area an addition area of 1.755 million ha and North-West another area of 0.645 million ha. Therefore, the forested coverage of the two areas can be increased to 55.6% by the year 2010.

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After 2010, great efforts should be made to maintain the balanced forested coverage as mentioned above by applying proper measures in management, exploitation and protection of watershed.

Solution 6 : Effective management and exploitation of flood control solutions : 

Solution 6 : Effective management and exploitation of flood control solutions Organize the observation station network of hydrology elements serving for the forecast and warning of potential flood and enhance the quality thereof. Organize the management of the basin and river system and flood control works in accordance with Decree on Flood control, Law on forestry planting and protection, Law on Water Resource, Environmental Law and other related laws and decree.

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Establish the reservoir regulation in order to bring into full play the downstream flood reduction efficiency and prevent the potential incidents basing on the appropriate coordination of existing flood control solutions. Increasing the community sense of the task and developing financial policies and structure to enhance the feasibility of structure and non- structure proposals. Promoting international cooperation, especially with China in terms of information provision in meteo-hydrology situations and basin conditions which relate the formation of flood and structural incidents.

Conclusion and recommendations : 

Conclusion and recommendations The traditional flood control solutions in the past and for the present time in Red River and Thai Binh rivers constitute a dyke system of 3000 km which have been formed for thousands of years and been constantly improved and reinforced. During the flood reason, the water level in river is already higher than that on farm from 3 to 6 m and then Red river is compared to a “ hanging river ”. The existing elevation and cross section of the dyke are equivalently accommodating the design flood water level in Hanoi of 13.60 m. This is the final limit of the dyke and for the safety of the dyke, the design flood water level will not be raised any higher.

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The upstream reservoirs are key structures for flood cutting and water level reduction in Red river and Thai Binh river delta to a level below the design level for the dyke system. According to the cascade flood study of Da and Lo rivers in the Red river flood planning reports and in Pre-feasibility study of Son La and Dai Thi works, it is recommended as follows : Da river : flood control capacity for downstream of 7 - 10 bil m3 Lo river : flood control capacity for downstream of 1 bill m3

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It is requested that the river bed, island, tributaries and flood drain channel be trained which include the definition of flood drain limit for different types of corridor as the removal of sub-dyke with narrow sections. The sub-dyke shall be maintained at warning level II once the water level of Red river rise so as to protect Ha Noi capital and divert flood into these areas Improvement measures is suggested for estuaries so as to maintain the flood drain capacity into the sea especially of such estuaries of Ba Lat, Day, Van Uc, Nam Trieu and Tra Ly. Ensuring the flood drain capacity in the flow condition in Son Tay for relevant design water levels in Ha Noi and Pha Lai.

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Growth and protections of watershed are traditional solutions for soil and water conservation, avoiding erosion and exhaustion, decelerating flood flow and controlling flash. Following the 5 million ha forestation program, by the end of 2010 we will be able to raise the wood coverage of the North-East and North -West areas to 55.6%. This also represents a long term solution but immediate efficiency can not be worked out for the time being. It means that not until 10 years later, can the system bring into its play in regulating the flow in both flood and dry seasons.

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On the Thao river, construction of a reservoir is impossible because of the large inundated area in the reservoir. Only medium reservoirs with flood reserve capacity of 1-2 billion m3 can be built in Lo river. The construction of Son La is the last opportunity of Da river which will meet the requirements in controlling flood for Red river and Thai Binh river downstream land If Son La reservoir has an cascade flood control capacity of 10 billion m3 and Dai Thi reservoir of 1 billion m3, we are quite capable of controlling against 500 and 1000 return period year without resorting on the flood diversion structures in Day river and other flood retention areas.