2.1.3.2. Data on water demands in study areas

According to Nielsen (2004), water demand is the amount required for a given purpose. The demand can be based on the present or future, and can be actual (i.e. related to an available infrastructure) or potential (assuming full infrastructural development and no raw water shortage). The serviceable (part of the) demand is limited both by infrastructure and raw water availability.

A distinction can be made between consumptive demand (for households, industries and agriculture), and non-consumptive demand (for fisheries, navigation, and environmental preservation).

a) Water uses in Preah Viear ( District of Chhaeb) and Stung Treng
(District of Stung Treng and the District of Thala Barivaat)

The use of water is the part of consumptive demand that is actually served at a given time. Many such uses generate a return flow, for example as sewage, or as irrigation tail water. The return flow can occur at a different time or place than the withdrawal, for example in case of a storage reservoir retaining water during part of the year and releasing it in a different part of the year. The use of water can be increased by infrastructural development and reduced by demand management.

An important part of the water resources analysis is to examine the scope for balancing the availability and demand of water under different assumptions about availability. During this analysis, a clear distinction should be made between water availability (or water resources generated), water demand, and actual water uses. This is in order to prevent ends and means being mixed up.

- Water consumption by industrial sector: No specific data is available for the Kratie Sub-area. The below data is general data at the national level. Water is necessary for all industrial activities, including cooling processing or manufacturing operations, power generation, cleanup and other sanitary purposes, and fire protection. The quality and quantity of industrial water demand varies significantly by industry and particularly uses, ranging from high water quality for the beverage industry to brackish water or treated municipal effluent for cooling purposes. Urban water usage is estimated at about 100 litres per person per day, for a total average annual supply of 36 million m³ for other urban centres in Cambodia.

- Water consumption by agricultural sector: No specific data is available for the Kratie Sub-area. Only general data related to the Lower Mekong Basin is presented below. Mekong river water is utilized for irrigation, hydropower generation, domestic and industrial purposes. Much of the water emerging from hydropower stations is also consumed downstream for irrigation, domestic and industrial purposes. Irrigated agriculture is responsible for 80 to 90 percent of water abstractions from the Basin (FAP from Mekong River Commission, 2002) and is utilised in the form of receding flood water storage, diversion of water from streams and from groundwater sources.

b) Industrial Demand in Takeo, Kandal, Kampong Speu, Prey Veng, Kampong Cham, Kamport, Koh Kong, and Phnom Penh

Water is necessary for all industrial activities, including cooling, processing or manufacturing operations, power generation, cleanup and other sanitary purposes, and fire protection. The quality and quantity of industrial water demand varies significantly by country, industry and particularly uses, ranging from high water quality for the beverage industry to brackish water or treated municipal effluent for cooling purposes.

According to the Basin Development Planning of the Mekong River Commission, Regional Sector Overview (2002), urban water usage is estimated at about 100 litres per person per day, for a total average annual supply of 36 million m³ for other urban centres in Cambodia. The total water usage represents about 0.01 percent of the flow in the Mekong River (Water Utilization Program, 2001).

It is assumed that most Phnom Penh Municipal wastewater transported to the Delta will travel via the Bassac River. However, with the distance from Phnom Penh to the Vietnam border (about 110 km), the large amount of dilution from the major river flows and high water temperature (about 29 degrees Celsius) in the Bassac River, the rate of decomposition of any organic matter discharged from Phnom Penh Municipality will be rapidly broken down and organic types of pollution are not likely to reach the border of Vietnam (Hart, 2001).

Most manufacturing and warehouses in Phnom Penh Municipality are located along the embankment of the Tonle Sap River north of the town or at the Bassac River south of the city mixed with commercial and residential areas. Such locations allow direct access to river transport and high consumption of water (Mekong River Commission, 2002i). The water requirement from the industrial sector is based upon the size of the factory. An estimate of water use volume for different sizes and types of factories are as follows (Cambodia National Mekong Committee, 2003):

• Major industry: 1,000 to 20,000 m³/day (for example: paper making, chemical manufacture, iron and steel production, oil refining etc.);

• Large scale industry: 100 to 500 m³/day (food processing, vegetable washing, drinks bottling, ice making, chemical products etc.); and

• Medium and small scale industry: 50 m³/day.

c) Agriculture uses in the Provinces of Takeo, Kandal, Kampong Speu, Prey Veng, Kampong Cham, Kamport, Koh Kong, Ratanakiri, Stung Treng, Mundulkiri, and Phnom Penh Municipality

Cambodia has inventoried 946 operating irrigation systems, which can service 256,120 ha of the two million ha wet season cultivated area. In the dry season, rice is grown on 225,000 ha and of this area, 143,490 ha are fully irrigated by receiving irrigation water from irrigation schemes. Hence, only 12 percent of the wet season rice is irrigable, the remainder being rainfed; just over half of the dry season crop is irrigated, the remainder being recession rice receiving supplementary irrigation from manually operated and diesel driven pumps. Very few of the irrigation schemes are capable of irrigating all year round.

Fully irrigated crops utilise approximately 10,000 m³/ha. Some irrigation engineers in Cambodia estimate that recession rice receives approximately 4,000 m³/ha of irrigated water.

The water consumption for rice is high compared to other crops. The total water consumption is dependent on crop type, stage of crop growth, soil type, irrigation method, and so on. The water consumption for different kinds of crops and for rice is presented in the table below.

Table 5: Water consumption within a critical period

Assuming that the water requirement during the critical period (February to May) for dry season irrigated rice and that for non-rice crops is approximately 0.8l/sec/ha and 0.6l/sec/ha respectively, the total water use for rice and non-rice crops is estimated at about 1,571 million m³/month and 509 million m³/month, respectively.

Table 6: Water consumption within the Delta Sub-area during a critical period

d) Ecological provincial demands of Takeo, Kandal, Kampong Speu,
Prey Veng, Kampong Cham, Kamport, Koh Kong, Ratanakiri, Stung Treng, Mundulkiri, and Phnom Penh Municipality

Ecological demand (of water) is a minimum stream flow or water level required for prevention of irreversible ecological degradation. The ecological demand varies from year to year and from place to place. The flow must be high in the wet season in order to maintain a healthy environment; for instance, fish species mainly rely on annual floods for their reproduction.

According to the Mekong River Commission (2003e), a value of velocity about 1 l/sec per km has been applied as an indicator for ecological demand in the dry season for Kok River basin. At the regional level, it is an important aim to preserve the Mekong Delta as a freshwater regime. This requires maintenance of a certain minimum flow, estimated at 2 l/sec per km (Nielsen, 2002).

e) Other provincial consumptions of Takeo, Kandal, Kampong Speu, Prey Veng,
Kampong Cham, Kamport, Koh Kong, and Phnom Penh Municipality

According to the Mekong River Commission (2003e), the consumption of water in the Mekong Delta fish ponds for aquaculture is approximately 6,000 m³/ha/month.

A study has shown that the total water use for tourists is much more than the local inhabitants, which affects the water use within the city and provincial towns. If the water use per tourist is approximately 0.5 m³/day, the total water use for the tourism sector within the Delta Sub-area is estimated to be 1.4 million cubic meters per year (including local and foreign tourists).

f) Water demand indicators

The following are the summarised water demand indicators for Cambodia at the present time:

- Total water demand/capita = 150 m³ per capita per year
- Share agriculture = 94%
- Share municipal and industrial = 6%
- Municipal and industrial withdrawal 1990 = 78 million m³
- Municipal and industrial withdrawal 2020 = 187 million m³

(Source: Ringler, 2001 in Mekong River Commission- Basin Development Planning Regional Sector Overview 2002)

- Total water demand = 0.5 Bm³ per year
- Internal water supply = 1,004 m³ per person
- Water for domestic use = 5%
- Water for industrial use = 1%
- Water for agricultural use = 94%

These figures will change due to future development in the Lower Mekong Basin that will bring about changes in the river hydrology (Source: CNMC, 2003).

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Table of contents > 2. River Basins > 2.1. The Mekong River System (Basin)

2.1.1. Introduction

2.1.2. Mekong River tributaries and Rainfall

2.1.3. Detailed survey of rainfall and surface water in the Mekong catchment

2.1.3.1. Data of river discharge in study areas

2.1.3.2. Data on water demands in study areas

2.1.4. Water environment in the Mekong River systems