This website is dedicated to the Chao Phraya delta. The delta is part of the (administrative) Central region. It is also sometimes called the Central Plain of Thailand.

Its boundaries depend on the definition given : we chose here to consider the area which is currently provided with irrigation facilities. Therefore, "Chao Phraya delta" or "Central Plain" is roughly referring here to the triangle joining Chai Nat, Phetchaburi and Chachoengsao and encompasses (see map) :

• The Greater Chao Phraya Irrigation Project ;
  

• the Greater Mae Klong Irrigation Project ;
  

• the lower Delta (West Bank, East Bank) ;
  

• three independent Irrigation Projects (Kra Siew, Nakhon Nayo, Khlong Priew) ;
  

• four irrigation subprojects bordering the Bang Pakong river ;
  

• some marginal areas located out of these hydraulic units, mainly along the Chao Phraya river and along the seashore ;
  

• Urban areas, first of all the Bangkok Metropolitan Area (BMA).
  

The gross area under consideration here covers 15,537,500 rai (i.e 2,486,000 ha), whereas the "official" irrigable area stands around 11 millions rai (1,760,000 ha) (Map 1). Its border is marked by important cities such as Chai Nat, Kanchanaburi, Lop Buri, Saraburi, Rachaburi.

Therefore it does not match the administrative Central Region, which, in addition, has different administrative definitions : the area generally referred to as "Central Region" extends from Trat Province, on the East, to Kanchanaburi, on the West, with the northern limit defined by Chai Nat Province (see Map 1). This Central Region, in more recent documents, sometimes appears divided in three sub-regions: the Central Region proper (Chai Nat, Phra Nakhon Si Ayutthaya, Lop Buri, Saraburi, Sing Buri, Ang Thong, Bangkok and Vicinity), and the Eastern and Western Regions.

The Chao Phraya Delta includes most of this Central region and parts of the eastern and western regions. Only the changwats (provinces) of Pathum Tani, Phra Nakhon Si Ayutthaya, Ang Thong, Sing Buri, Nakhom Pathom, Samut Songkhram and Bangkok are totally included in the Delta.

Map 1 : Administrative regions

Map 2 shows the main cities and the changwat which contribute to the Central Plain. Only those of their amphoes which are included in the Central Plain are indicated, giving a total of 110 amphoes (+ Bangkok Metropolitan Area), and a total gross area of 2,765,800 ha (17,286,250 rai). It is worth noting that some of these changwats, especially along the western limit, have a significant part of their area located in the rainfed neighbouring areas. Statistical data corresponding to these amphoes must therefore be interpreted cautiously.

Map 2

Together with the administrative level of amphoes, the hydraulic units constituted by the sub-Projects of the Royal Irrigation Department will be considered. The forty three sub-projects belong to four Regional Irrigation Offices : the 10th Region (Head office in Kanchanaburi, for the Mae Klong Project), the 7th Region (Head office in Chai Nat, for the Chao Phraya right bank), the 8th (Head office in Lop Buri, for the Chao Phraya right bank), plus the 9th Region (for the Bang Pakong area).

Figure 1 gives an overall sketch of the study area : with a gross acreage of 2.5 million ha, among which 2.2 is under the administration of the Royal Irrigation Department, approximately 1.9 million ha can be considered irrigated. Rice cropping covers 1.2 million ha.

Figure 1

     The map 3 indicates the name and location of the sub-project of each main project :

• Orange : Upper delta

• Green : Lower delta - west bank

• Dark blue : Lower delta - east bank

• Pink : Mae Klong

• Yellow : Bang Pakong area

• Light blue : Other projects

Map 3

 Map 4 shows the layout of the different irrigation projects, with the diversion dams and main canals :

• Red : Main canal (gravity areas)

• Pink : Secondary canal (gravity areas)

• Blue : Main channel (conservation areas)

• Green : Secondary channel (conservation areas)

Map 4