Chao Phraya Watershed

The expanse of the Chao Phraya River and its tributaries, i.e. the Chao Phraya river system, together with the land upon which falling rain drains into these bodies of water, form the Chao Phraya watershed. The Chao Phraya watershed is the largest watershed in Thailand, covering approximately 35% of the nation's land, and draining an area of 157,924 km². The watershed is divided into the following basins:

*Pa Sak Basin
*Sakae Krang Basin
*Greater Nan Basin (comprising the Nan Basin and the Yom Basin, and usually divided as such in drainage analyses)
*Greater Ping Basin (comprising the Ping Basin and the Wang Basin, and usually divided as such in drainage analyses)
*Tha Chin Basin (the basin of the Chao Phraya's most significant distributary)
*Chao Phraya Basin (the land drained by the Chao Phraya River itself, and not by its major tributaries)

The mountainous natural boundary of the watershed forms a divide, which has, to some degree, historically isolated Thailand from other Southeast Asian civilizations. In fact, in northern Thailand, the divide roughly corresponds to a long section of the political border of present-day Thailand. Southern portions of the divide's boundary correspond less to the nation's political border, because isolation in this area was prevented by the ease of transportation along the lowlands surrounding the Gulf of Thailand, allowing a unified Thai civilization to extend beoynd the watershed without issue.

2007 Flooding in Phitsanulok, Thailand

Deforestation and urban development along the river banks in the region, combined with seasonal downpours in the Phetchabun Mountains have led to severe flooding in recent years within the province. Flooding in the province in 2007 was described by the Bangkok post as the worst floods in 40 years. On October 4, 2007, 100 rescue workers and 100 soldiers were dispatched to assist stranded residents in tambon Chompu and tambon Ban Mung, where water levels rose more than a meter. On that same day, Phitsanulok Governor Somboon Sripattanawat declared the Noen Maprang District a disaster zone. On October 6, 2007, Pongsagorn Kaenmanee, age 9 was among the first to drown in the flood waters. By October 8, 2007, the floods had killed at least three people in the Wang Thong District, and that district, in addition to Noen Maprang, was declared a disaster zone. On October 8, 2007, Deputy Prime Minister and Social Development and Human Security minister Paiboon Wattanasiritham visited the Phitsanulok Province to assess and address the flooding issues in the province. On October 10, 2007, the Office of Disaster Prevention and Mitigation sent boats out to deliver food and water supplies to residents of Bang Krathum District, which was cut off by floods. On October 12, 2007, the flooding took the life of a fifth villager in the province, who drowned after being swept away while he was rowing his boat to cast a fishing net. On October 14, 2007, flood water pressure sent inflows through the Mueang Phitsanulok Municipality's sewage system, flooding three communities. On October 15, 2007, the Royal Irrigation Department announced plans to construct six dams on the Wang Thong River as an attempt to solve the problem of seasonal flooding. On October 16, 2007 Thung Salaeng Luang National Park was temporarily closed for fear that tourists may become trapped in its caves by flood waters (This was prompted by an incident in Surat Thani's Khao Sok National Park where a group of cave exploring tourists drowned). A meeting of senior officials is scheduled for October 31, 2007 to discuss the progress of an environmental impact assessment (EIA) of the dam proposal. At least one of the dams will be in Thung Salaeng Luang National Park, but officials ensure that it will not be built in a wildlife sanctuary area. Flooding in the region is a recurring problem in Phitsanulok Province this time of year. In 2006, for example, between August 20 and December 13, over 22,000 people in 70 villages within Phitsanulok were affected by flooding, and over 1800 acres of farmland and 194 roads within the province were submerged by flood waters.