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  Natural conditions

Hydrography

1. Density of rivers and arroyos

Beside Hau River and Co Chien River, the arroyo system in the field is quite developed, which is widen and deep at the estuary, gradually narrow and shallow toward the inner field. The major systems include:

- In the side of Co Chien river: Lang The arroyo, Tra Vinh channel, Bai Vang and Thau Rau arroyos.

- In the side of Hau river: My Van arroyo, Can Chong river, Tra Cu, Tong Long and Vam Ray  arroyos, Lang Sac channel (Nguyen Van Pho).

- The system of ordinate channels: Tra Ngoa and 3/2 channels, which are unified and responsible to provide freshwater for each area.

In general, the density of ordinate canals in the province is distributed quite equitable, from 4-10 meters per hectare. The density of inner field canals is still low (under 50% in comparison to the production requirements). The district having the highest density of channel of the province is Tieu Can (45 meters per hectare); the lowest ones are Duyen Hai, Tra Cu and Cau Ngang districts (18 - 28 meters per hectare).

2. Hydrographic systems

The whole province is influenced by the East Sea tidal regime via two large rivers and the interlacing canal system. This is an irregular semi-diurnal tidal regime, with two times of flood-tide and two times of tidal flow each day. Every month, there are two periods of floodtide (on the lunar 1st and 15th day) and two periods of tidal flow (on the lunar 7th and 23rd).

For being nearby the sea, amplitude and level of water on the rivers and arroyos are rather high, resulting in the high potential of water drainage in the province. Only part of Cang Long and the central area of the province (neighbouring area of districts: Chau Thanh, Tieu Can, Tra Cu and Cau Ngang) are flooded for 3-4 months due to the border of water from many different directions and rapid tidal amplitude.

In general, about one third of natural land of the province is quite heavily flooded in the rainy season (over 0.6 meter), which are distributed mainly along the riversides and sunken areas of Cau Ngang, Duyen Hai and Tra Cu districts. Although it is drained easily, this flooded level has limited the intensive cultivation of winter crop, such as putting down fertilizer, planting high-yield rice varieties. Other low flooded mounds (under 0.4 meter) are distributed mainly in the central area of the province (belong to the high-yield rice area). This is an area having capacity of fruit cultivation and high-yield rice variety intensive cultivation, but easily being affected by drought.

Because it is affected by salty water, although the tidal motive power is high, only part of area in the province can use freshwater to water automatically and mainly in the less salinity areas (2-3 months).

3. Salinity situation:

Annually, there are about 90% of natural soil of the province are encroached by salty water with the length of encroached sea water (4 grams per liter) is 30 kilometers to land from the sea. The salty encroachment usually starts from December at Hung My on the rivers of Co Chien and Tra Kha on the Hau river. The highest level is in April at the Vung Liem estuary (on the Co Chien River) and Cau Quan (Hau River). The salty encroachment is normally finished in June – depends on the time and rainfall at the upper reaches and in local area.

Basing on the limit of salinity 4‰, the province can be divided into 6 areas affected by salinity as following:

- Regular salinity areas (more than 4‰ per year): accounted for 17.7 % of agricultural areas.

- 5 - 6 month salinity areas (from solar January to June): 25.8%

- 4 month salinity areas (from solar February to May): 13.9%

- 3 month salinity areas (from solar March to May): 16.6%

- 2 month salinity areas (from April to May): 1.8%

- 2 month unusual salinity area (from solar April to May): 15.1%

In deed, the stable cultivation of two crops only limits in the salinity areas of under 4 months. As for part of the area of Cau Ngang and Duyen Hai districts, the time of salinity is too long, the source of freshwater is limited but the rainfall and raining time is low causing difficulties to agricultural production. It is only suitable to aquaculture and forestry.

In conclusion: In terms of hydrometeorology, Tra Vinh province has many unfavourable conditions for agricultural production, but part of area can be an advantage of aquaculture and forestry. In agriculture, taking full advantage of existing conditions, cultivating in time is very important and irrigation need to proceed to be a basis for the development of agriculture.

     

Climate

1. Meteorological:

Located in the Mekong Delta, Tra Vinh province also has common advantages, such as: rich radiation light, high and stable temperature. However, due to the distinct characteristics of the inshore climate area, Tra Vinh province has some limits in terms of climate, such as: strong northeast wind, high evaporating level and little rain, etc.

Temperature: The average temperature of the whole province is 26.60C, temperature amplitude between the highest: 35.80C and the lowest: 18.50C; temperature amplitude between day and night is low: 6.40C. In general, the temperature is fairly harmonized and the discrimination of 4 seasons is not clear, only dry and rainy seasons.

2. Radiation:

The duration of sunshine in the province is 7.7 hours per day, photosynthesis radiation is abundant: 82,800 cal per year, which enables crops to grow in the whole year. However, with the current method of cultivation, this energy source is not utilized much, especially in the dry season.    

3. Moisture: Annually average moisture ratio varies from 80 - 85% and tends to change in accordance with season; 79% in dry season and 88% in rainy season. The average moisture of all months is often more than 90% that creates favourable conditions for the development and spreading of some epidemic diseases.

4. Wind:

There are two types of major winds:

South westerly monsoon: from solar May to October, winds with steam blow from the sea in the west causing rain.

Northeast wind (South northerly or south easterly monsoon): it is most widespread from November to next March in the direction in parallel with large estuaries. Northeast wind is the cause of high rising seawater and pushing the salty water deep into the inner field. The speed of wind is strongest during solar February and March (with the speed of 5-8 meters per second), especially in the afternoon. Therefore, the appearance of salty crest because of the effect of northeast wind has affected the production during this period.

5. Hoarfrost:

Hoarfrost appears annually, especially in the year-end months, from solar December to February the next year due to the effect of following factors: high moisture at the end of rainy season combined with lowest temperature for one year and the widespread of northeast wind. Containing a considerable salt content in the air, hoarfrost has affected much to the growth of cultivated crops.

6. Evaporating:

Total evaporating volume of the whole province is rather high with the average of 1,293 mm per year. In dry season, the evaporating volume is from 130 - 150 mm per month, especially in the high sand mound and the area close to the sea, causing the severe drought in these areas. As for Duyen Hai district, the evaporating volume is higher than the annual rainfall causing the capillarity of salt up and concentrated on the surface layer. That makes soil worse and hard to cultivate.

7. Rain:

Total rainfall is from the medium down to low level (1,588 – 1,227 mm), distributed not fairly and strongly split in accordance with space-time. The rainfall reduces gradually from North to South, highest in Cang Long, Tra Vinh and lowest in Cau Ngang and Duyen Hai.

As for the duration of rain, up to 90% of rainfall occurs in rainy season, started from May to November. The closer toward the sea, the shorter duration of rain occurs, that means the rainy season starts late but finishes early. This is a significant limit to the production of this area, because the useful rainfall for cultivated crops is little. Districts enjoy the longest time of rain are Cang Long (118 days), (Tra Vinh township 98 days); those enjoy shortest time of rain are Duyen Hai (77 days) and Cau Ngang (79 days).

According to the statistics in the last 10 years, with the frequency of 75%, the rainy time of all districts is as following:

 

District

Start raining

Finish raining

Cang Long, Tieu Can, Cau Ke

15/5 - 16/5

26/10 - 7/11

Chau Thanh, Tra Vinh

15/5 - 16/5

26/10 - 7/11

Cau Ngang, Tra Cu, Duyen Hai

22/5 - 27/5

24/10 - 26/10

 

8. Drought:

Drought occurs annually causing many difficulties for production, with the number of rainy days is not continuous, from 10 – 18 days. Cau Ke, Cang Long and Tra Cu are districts rarely influenced by drought. Tieu Can district is often seriously influenced by drought in the beginning of the crops (in June and July, while others, such as Chau Thanh, Cau Ngang and Duyen Hai, are more severely influenced in the mid-crop (in July and August).

Area

Total natural area is: 222,515.03 hectares. (According to the statistics of land in 2003), of which: 

- Land for agriculture:                              180,004.31 hectares 

- Land for forestry:                                       6,080.20 hectares 

- Specialized land:                                      9,936.22 hectares

- Housing land in rural area:                       2,805.66 hectares 

- Housing land in urban area:                        445.70 hectares 

- Unused land:                                           22,242.94 hectares

 

Geographical location

Tra Vinh is a province in the Mekong Delta. The geographical location limits from 9031’46’’ to 10004’5” Northern latitude and from 105057’16” to 106036’04” eastern longitude.

- Bordered with Vinh Long province in the north and north western.

- Bordered with Ben Tre province in the east, sharing Co Chien River.

- Bordered with Soc Trang province in the west, sharing Hau River.

- Bordered with East Sea in the south and south eastern with more than 65 kilometers of coastal line.

The central township located on the Highway No.53, 200 kilometers far from Ho Chi Minh City and 100 kilometers far from Can Tho City. Total natural area is 2,225 square kilometers, accounted for 5.63% area of the Mekong Delta and 0.67% area of the whole country. Tra Vinh province has 7 districts and one township, namely Cang Long, Tieu Can, Cau Ke, Chau Thanh, Tra Cu, Cau Ngang, Duyen Hai districts and Tra Vinh Township.

 

                                                            

Total natural area is: 222,515.03 hectares. (According to the statistics of land in 2003), of which:

- Land for agriculture:                              180,004.31 hectares

- Land for forestry:                                       6,080.20 hectares

- Specialized land:                                      9,936.22 hectares

- Housing land in rural area:                       2,805.66 hectares

- Housing land in urban area:                        445.70 hectares

- Unused land:                                           22,242.94 hectares

Terrain

 The terrain of Tra Vinh province bears the nature of inshore delta with sand mounds, continuously spreads in the shape of arc and in parallel with coastline. These sand mounds become higher and larger toward the sea. Due to the partition of mounds and the system of criss-crossed roads and canals, the terrain of the whole area is quite complicated: depression areas come between high mounds and the slope represented in each specific field.

In general, common ground level of the province is from 0.4 – 1.0 m, accounted for 66% of natural land area.

The highest terrain (>4m) includes: sand mounds distributed in Nhi Truong and Long Son communes (Cau Ngang district); Ngoc Bien commune (Tra Cu district); Long Huu commune (Duyen Hai district).

The lowest terrain (<0,4m): mainly concentrated in depression fields in Tap Son, Ngai Xuyen and Ngoc Bien communes (Tra Cu district); Thanh My (Chau Thanh); My Hoa, My Long, Hiep My (Cau Ngang); Long Vinh (Duyen Hai).

 With such a terrain distribution, it can be remarked as following:

- The complicated terrain of Tra Vinh province has formed a diversified and abundant production basis, such as: food cultivation, foodstuff, fruit crops on sand mounds. Rice trees predominate in the medium and low areas, some riverside depression areas are suitable to breed shrimp naturally.

- The partition of sand mounds has created many difficulties to build irrigation canals, quickly gather rain water causing flood for depression areas among mounds.

In general, the favourable terrain for agricultural production is from 0.6-1 meter. This ground level is suitable for self-drainage, rarely causing drought as well as flood. As for the forest in Duyen Hai district, the 0.4 - 1 meter ground level is suitable for the development of almost all kinds of trees in salt-marsh area, such as mangrove, leave, avicennia, etc.

 
Natural resources – Aquaculture resources

Forest and forest-land in Tra Vinh province spread on an area of 24,000 hectares along 65 km coastline, including the whole Duyen Hai district, My Long commune (northern, southern) of Cau Ngang district and Don Chau, Don Xuan communes of Tra Cu district.

Land areas covered with forest are 13,080 hectares, of which: cypress forest accounted for 640 hectares; mangrove 742 hectares; salty-flooded forest 50 hectares; eucalyptus forest 100 hectares; mangrove palm 4,159 hectares; date-palm forest 605 hectares; non-fertilized forest 6,784 hectares.

Non-forest areas accounted for 10,884 hectares, of which: bushes 6,937 hectares; unoccupied land 2,809 hectares; warp 1,138 hectares.

In the past, the forest was thick with many valuable forestry products, not only meet the demand of the local people but also export to neighbouring areas. Nowadays, the area of forest has been reduced significantly. The natural forest only includes pure cypress, most of area of forests has been become unoccupied land or scattered, wood reserves are negligible, the ability to naturally recycle is low, protective role is weak.

Up to 1994, there had been only 6,120 hectares remained value, including 640 hectares of cypress, mangrove 580 hectares; avicennia 400 hectares; eucalyptus 100 hectares; leaves 4,400 hectares. 18,000 hectares forest land and scattered bushes accounted for 3.81% of natural area. Forestry land has been reduced because of excessive exploitation (blank chopping) and utilizing forest land to plant aquaculture. According to the geographical statistics in 1997, the forestry area remained only 9,004 hectares.

There are 73 types of fugitive plants belong to 5 branches, mostly concentrate on Silic seaweed industry and other seaweed groups originated from salt-water. The medium density reached 666/individual per litter. There are 48 types of ephemerous animal, those are in inshore areas reached an average of 15,600 individuals per cubic meter (varying from 4,000-34,000 individuals per cubic meter. The bottom fauna of the seawater area of Tra Vinh province is quite abundant.

The area of natural valley of the province is 21,265 hectares and about 98,597 hectares flooded from 3-5 months per year, the volume of inner field aquatic products is estimated at 3,000 – 4,000 tons, regularly exploit from 2,000-2,500 tons. The inshore aquaculture source of income includes that of river mouths, mangrove forests and inshore water area from the depth of 30-40 meters towards the land. The inshore source of fish includes 40 families, 78 varieties and 150 races of inshore sea fishes, brackish fishes and immigrant fishes. The volume of fish in the river mouth of Tra Vinh in 1994 was 62 tons (the river mouth), 274 tons of mid-layer and brackish fishes; that of salty and brackish areas were 9,063 tons. Total amount of fish of the river mouth and inshore area is 72,869 tons with the potential capacity of exploiting (50%) is 36,434 tons.

Dinh An shrimp ground with the area of about 20,000 hectares is one of five largest ones in the inshore line of the Mekong Delta. It is estimated that the reserves of shrimp at the two major grounds are 97-212 kilograms per hectare (Bac Cung Hau) and 64-249 kilogram per hectare (Dinh An river mouth), respectively; current total volume of salt-water shrimp of Tra Vinh is about 4,300 – 11,000 tons per year. There are 11 races of crayfishes, which stand behind salt-water shrimps in terms of economic value, in the valley area of Tra Vinh, including giant river prawn, egg-shrimp, little prawn, freshwater shrimp. Annually, it can be exploited 2,000-3,000 tons of cuttle, 35-49 tons of blood cookle and 168-210 tons of oyster.

 

Natural resources – Forest and land

Tra Vinh is located in the lower section of the Mekong Delta with the height of terrain from 0-5 meters. Geologically, the whole province is young sediment originated from river and sea alluvium, therefore, mineral reserves in Tra Vinh are mainly filling sand, not much building sand and little clay.

1. Sand

Building sand

Distributed in high mounds 3-3.5 meters, in the shape of arc and parallel with coastline, 5-10 kilometers long, 50-70 meters wide. By geological surveys on sand mounds in Phuoc Hung, the geological section is as following:

- Upper layer: whitely grey sand powder, of which powder accounts for 70% and sand 30%, the thickness is about 4 meters.

- Lower layer: smooth grain to medium grain, friable, 1.5-2 meter thick, mainly is quartz and mica. Percentage of components include:

 •    Medium grain sand (0.50 – 0.25 mm) = 3.4 %

 •    Small grain sand (0.25 – 1.10 mm) = 95.15%

•     Clay powder (under 0.10 mm) = 1.45%

Reserves of building sand in Phuoc Hung is about 810,000 cubic meters and used for construction.

Besides, there are also sand mounds in Duyen Hai and Cau Ngang districts
       

River sand

Preliminary surveys show that the section of Tien River bordered with Tra Vinh township has a small reserve, suitable to serve for filling up in construction and can exploit from 30,000 – 50,000 cubic meters per year.

As for Hau River side, most of mounds are mud. Sand is found in the area of Hoa Lac hamlet, Hoa Tan commune with small reserve that can exploit 30,000 cubic meters per year.

2. Clay

In 1996, while planning the geological – mineral map of the Southern delta, the Geological Group No.204 took samples at 4 palces: Tra Luot (2), Phuoc Hung (3), Tra Cu (5) and Cam Son (1). In these areas, people had exploited clay to produce brick at small scale of the reserves of 2.65 cubic meters in total but bricks were warped and heavy, not suitable to the demand of market, that made the brick industry in the area did not survive for long.

 

Name of mine

Number sign on the map

Sand (%)

Powder (%)

Thunderball (%)

  Cam Son

1

1,0 - 7,7

6,8 - 22,0

77,0 - 85,5

  Tra Luot

2

14,2

16,7

69,1

  Phuoc Hung

3

1,0 - 3,0

19,0 - 22,0

75,0 - 80,0

  Tra Cu

5

0,4

7,5

93,1

       

Mineral ingredients of clay are mainly Hydromica, then Monmorilnit and Kaolinit as the least.

Chemical components: of the sample taken in Tra Luot: SiO2 = 53,7 - 62,3%, Al2O2 = 17,5 - 19,1%, Fe2O3 = 4,3 - 13,0%, MKN = 7,6 - 9,1%

 

Mine

Plastic indicator

Absorbent ratio (%)

Shrinking ratio in air (%)

Shrinking ratio in burning  (%)

Press resisting ratio (%)

  Cam Sơn

25,4 - 25,6

 

11 – 12

12 - 13

120 – 150

  Phuoc Hung

21,3 - 22,2

11 - 13

9 – 10

9,5 - 11

140 – 220

  Tra Cu

 

12,1 - 13,6

7 – 8

8 - 9

170 – 180

 

Clay contains little sand and much clay.

Chemical components of clay meet the requirements of the Ministry of Construction. In terms of mineral, clay contains much Hydromica that makes bricks easy to be warped, not suitable to produce tiles.

The suitable burning temperature is 9500C

3. Mineral water (Geothermy)

Mineral water mines are distributed in Long Toan townlet, Duyen Hai district. The Bicacbonat Natri component in water is quite high that reaches the national standards at the temperature of 38,50C and can exploit 2,400 cubic meters per day.

 

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