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โครงการหนังสืออิเล็กทรอนิกส์ด้านการเกษตร เฉลิมพระเกียรติพระบาทสมเด็จพระเจ้าอยู่หัว

Water availability (million m /year)
3
Watersheds
Stored water Surface water (Rainfall) Total
Khong 1,719 88,356 90,075

Chi 2,280 68,549 70,829

Mun 2,546 96,929 99,475
Chao Phraya 63 25,037 25,100
Sakae Krang 232 6,619 6,851

Pasak 1,145 18,281 19,425

Thachin 323 16,130 16,453
Mae Klong 288 34,890 35,178

Petchaburi 750 6,381 7,132
West Coast Gulf 650 9,367 10,017

Prachin Buri 153 16,449 16,601
Bang Pakong 623 16,837 17,459

Thole Sap 140 11,104 11,244

East-Coast Gulf 808 29,558 30,365
Peninsula-East coast 169 58,684 58,853

Tapi 161 26,823 26,984
Thale sap Songkhla 53 17,909 17,962

Pattani 2 8,709 8,711
Peninsula-West coast 57 56,200 56,258

7.1.3 Estimation of Variation factor (VF)

The variations in monthly or annually rainfall in each regions of Thailand have been
accounted for in the assessment as the variation factor (VF) for calculating the weighted WTA as

shown in Equation (8). Based on the standard deviation of monthly average (S* month ) and annual
rainfall (S* ) derived from the rainfall data during years 2002-2011 (as shown in Appendix II), the
year
variation factors for each basin in the case of strongly regulated flow (SRF) and non-strongly
regulated flow (non-SRF) can be estimated. The water storage as dam or large and medium

reservoirs is supposed to be the SRF case in the study and the adjusted WTA ratio is categorized
into SRF if water is delivered from the water storages; otherwise, the adjusted WTA ratio is

classified as non-SRF. Regarding the classification, the variation factor and the adjusted WTA are
calculated based on the SRF case as shown in Table 7.7.

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