HCM City has an area of approximately 2,094 square kilometers. It is located from 10 10’-10 38’ North and 106o2’-106o54’ East. The city has Binh Duong Province in the north, Tay Ninh Province in the northwest, Dong Nai Province in the east and northeast, Ba Ria-Vung Tau Province in the southeast, and Long An and Tien Giang provinces in the west and southwest.
HCM City is 1,730km from Hanoi by land and is at the crossroads of international maritime routes. It is also at the center of Southeast Asia. The city center is 50km from the East Sea in a straight line. It is a transport hub of the southern region and a gateway to the world, having the largest port system and airport in Vietnam. Saigon Port can handle 10 million tons of cargo a year. Tan Son Nhat International Airport, 7km from the city center, has tens of international routes.
Geology and soil
The soil of HCM City was formed upon two sediment classes: Pleixtoxen and Holoxen.
The Pleixtoxen sediment: This ancient alluvial sediment covers most of the northern, northwestern and northeastern parts of the city, encompassing Cu Chi, Hoc Mon, northern Binh Chanh and Thu Duc districts, north and northeastern District 9, and old inner-city areas.
Main characteristics of the sediment class are hilly terrain, with a depth range of three to 25 meters, and oscillation in the southeastern direction. Due to the combined effects of natural factors, including creatures, climate, time and human activities, and erosion and decomposition, the sediment class has developed into grey soil. Grey soil makes up 45,000 hectares or 23.4% of the city’s total soil area.
In the city, there are three types of grey soil: highlands grey soil with some impoverished places, grey soil with red and yellow-speckled layers, and gley grey soil. Soils of the two first types make up most of the total area. In general, the main mechanical constituents of grey soil are sandy soil mixed with heavy soil. The grey soil therefore has a poor water-containing ability. The underground water levels change from place to place and from season to season with a range of one to 15 meters. This is acid soil, as it has a pH of around 4.0 to 5.0.
The grey soil is of low fertility but has thick layers which are suitable for growing agricultural and forestry trees with high yielding and economic efficiency if rotational and intensive cultivation is implemented properly. Also, the foundation of grey soil is appropriate for infrastructure constructions.
The Holoxen sediment: This new alluvial sediment of HCM City had its origin in coastal areas, bays, riverbeds and alluvial plains and consequently formed different types of soil. Specifically, alluvial soil makes up 15,100 hectares or 7.8% of the total area; aluminum soil is 40,800 hectares or 21.2%; and alkaline soil is 45,500 hectares or 23.6%. The remaining area, 400 hectares or 0.2%, is made of sandy soil near the ocean and yellow-brown feralite soil on hills that have eroded.
+ Alluvial soil: Formed in the highlands terrain, which is as deep as 1.5-2 meters, mainly in the southern Binh Chanh District, the eastern part of District 7, the northern Nha Be District and some places in Cu Chi and Hoc Mon districts.
The alluvial soil is classified into three types: alluvial soil with speckled layers, gley alluvial soil, and sweet alluvial soil. The two first types make up a vast area while the third type, which is fertile, covers around 5,200 hectares or only 2.7%. The main mechanical constituent of the alluvial soil is clay with a medium to high amount. Surface layers have a pH of 4.2 to 4.5. The pH degree of deeper layers is up to 5.6 or 6.0 but the acidity is higher. The soil has a medium humus content and fairly high nutrient content. In general, the alluvial soil is fertile and suitable for growing high-yielding paddy.
+ Aluminum soil is classified into two types: with high aluminum content or with a medium content. The high-aluminum type is mainly concentrated in the city’s southwestern area from Tam Tan-Thai My of Cu Chi District to the southwestern part of Binh Chanh District. In the area, the soil is high-aluminum and a pH of 2.3 to 3.0. The area’s soil has the same constitution and characteristics as the aluminum soil of the Mekong Delta region.
The medium-aluminum soil is concentrated along the Saigon River, Tra Canal and in District 9. The soil here has a pH of 4.5 to 5.0 on surface layers but down to 3.0 to 3.5 in deeper layers.
The main mechanical constituent of the aluminum soil is tight-packed clay. The soil, which is one meter deep or less, is softer due to high humus content. The soil has a medium nutrient content. The content of toxin ions is high and consequently the alkaline soil is not suitable for paddy growing.
With irrigation methods taken to reduce the amount of aluminum, the soil can be improved for cultivation and local farmers can raise annual crops from one to two. The aluminum soil is suitable for growing pineapples, sugar canes, cashew trees and industrial trees including cajuput, eucalyptus and some kinds of cuasia.
+ Alkaline soil: This makes up the largest area in HCM City and it is mainly concentrated in Nha Be and Can Gio districts. There are two types of alkaline soil: seasonal alkaline soil and salt marsh.
Seasonal alkaline soil covers 10,500 hectares of Nha Be and northern Can Gio districts. The soil is covered with salt water from December to June or July. The soil is rich and has a high content of humus and a pH of 2.4-2.7 at deep layers.
During the flooding season, the salt water is diluted for four to five continuous months. In the period, the soil is covered with an alluvial layer as deep as 20-30 centimeters so that farmers can grow a crop of paddy with average yield of two tons per hectare.
To gain greater efficiency, the region has carried out crop and husbandry restructuring and given focus to growing fruit and forest trees and breeding shrimp.
Salt marsh soil accounts for 35,000 hectares of the majority of Can Gio District. The ground is heavy and dark grey. The soil has a high content of nutrients and a pH of 5.8-6.5. The soil is suitable for developing mangrove forests in order to serve land protection against sea encroachment and to foster the eco-tourism development along the city’s southern coastal area.
The two types of alkaline soil have a weak base and therefore cause difficulties in infrastructure construction. However, the condition is favorable for waterway traffic development as rivers and canals account for up to one-third to the total area of the alkaline soil.
HCM City belongs to a transitional region between the southeastern and Mekong Delta regions. The general topography is that HCM City terrain gets lower from north to south and from east to west. There are three types of terrain.
The high terrain lies in the northern-northeastern area and part of the northwestern area encompassing northern Cu Chi, northeastern Thu Duc and District 9. This is the bending terrain with average height of 10-25 meters. Long Binh Hill in District 9 is the highest at 32 meters.
The depression terrain lies in the southern-southwestern and southeastern part encompassing districts 9, 8, 7, Binh Chanh, Nha Be and Can Gio. The area’s height is in the range of 0.5 to 2 meters.
The medium-height terrain lies in the middle of the city, encompassing most old residential areas, part of districts 2 and Thu Duc, and the whole of districts 12 and Hoc Mon. The area’s height is 5-10 meters.
In general, the topography of HCM City is not complicated but fairly diverse and therefore has good conditions for multi-faceted development.
The ecology of HCM City is classified into three typical systems based on the natural conditions: The tropical rainforest, the alum flooded forest, and the mangrove forest. The primeval forest almost no longer exists. However, a study of the forest is expected to help restore and develop a good ecological system for a large city in this tropical region.
The tropical rainforest
This forest exists in Cu Chi and Thu Duc districts. According to some research, the primeval forest in Cu Chi is a closed evergreen forest with the dominant plants being the dipterocarpaceae, the deciduous leguminosea and the lythraceae grown in the salient and umbelliferous layers. The dipterocarpaceae can be found at the secondary forest in Ben Dinh tunnel complex, with five species: dipterocarpus intricatus, shorea cochinchinensis, anisoptera costata, hopea odorata, and a famous species of precious wood that includes dalbergia bariensis, sindora siamensis, dalbergia cochinchinensis, dialium cochinchinensis, xylia dolabriformis and lagerstroemia tomentosa. The sub-canopy layer of the forest is home to the strychnos nux vomica, croton sp, peltophorum dasyrachi, grewia paniculata and wrightia annamensis. The forest in Cu Chi is damp and a little dry similar to that in Samat-Ca Tum in Tay Ninh Province, which is on ancient alluvial soil with a high content of sand and a wavelike territory.
The primeval forest in Thu Duc is like the typical tropical forest in the southeastern region, such as those in Ho Nai, Trang Bom and Ma Da in Dong Nai Province. It has a wavy territory with soil composed of ancient alluvia and several kinds of stones. The dominant trees are the humid dipterocarpaceae species such as the dipterocarpus alatus and dipterocarpus dyeri.
In the past years, along with the protection of the remaining secondary forests, mainly the coppice forest around Ben Duoc tunnel complex, Ben Dinh and Ho Bo in Cu Chi, efforts have been made to restore the closed evergreen forest and plant forests with large and precious wood. Also, a project to develop a botanical garden and a historical forest has been implemented. Another project is to build the national cultural and historical park on an area of 400 hectares in Long Binh in District 9, with the creation of a vegetation cover being one major goal. ·
The alum flooded forest
The natural vegetation on alum flooded land in HCM City is very poor. Large natural malaleuca leucadendron forests in southwest of Cu Chi, Binh Chanh, Hoc Mon and Nha Be districts almost no longer exist due to human exploitation and farming. Only some stretches of bush trees and several hectares of cultivated malaleuca trees are protected at the Tan Tao Experimental Station in Binh Chanh. This lowland area is home to the heleocharis dulcis, ischaemum indicum, acrostichum aureum, nymphea stellata and utricularia flexuosa. The highland area has the saccharum spontaneum, phragmites karka, acrocnychia laurifolia, annona glabra, melastoma affine, gardenia jasminoides and some species of leane.
After 1975, new economic settlements and farms were developed on alum land. Many kinds of crops and fruit trees were grown, such as paddy, sugarcane and pineapple. In addition, forest and tree planting were developed strongly, especially the acacia auriculiformis, acacia mangium and sesbania grandiflora. As a result, the alum flooded environment in the outskirts was improved and developed well. ·
The mangrove forest
The mangrove forest is mainly in Can Gio District, south of HCM City. It is a primeval forest developed along with the formation of alluvial ground at river estuaries and sea mouths. The dominant plant is the big-size rhizophora apiculata. The flora is diverse with 104 species of 48 families. Under French rule, the forest was a protected area. However, during the 1961-1970 period 80% of its area was destroyed by toxic defoliants sprayed by the U.S. military. During 1978-1986, HCM City authorities had tens of thousands of hectares of mangroves restored. In the brackish water area north of Can Gio, there are the nypa fruticans, cajuput, eucalyptus and cashew groves.
In general, the distribution of vegetation in mangrove forests depends on tide floods and soil solidity. Most vegetation familiar in mangrove forests in the South exists in Can Gio and is distributed according to different levels of terrain. They are the avicennia alba, avicennia officinalis, sonneratia alba, ceriop tagal, avicennia alba, phoenix paludosa, acrostichum aureum, excoecaria agallocha, lumnitzera racemosa and others.
With restoration efforts, the ecology of Can Gio mangrove forest has been improved. Animals have returned, such as crocodiles, monkeys, foxes, pythons, snakes and many bird species. Shrimp and fish production has also increased.
Besides protecting the land from encroachment by the sea, the Can Gio mangrove forest plays the role as a “lung” of HCM City, regulating its atmosphere. It also serves as a tourist area.