Other Important Aspects Of Water Availability

It is felt that the computations of water availability on mean year and 4 out of 5 year basis are not sufficient to give a clear picture for proper assessment of the situation. It is therefore necessary to examine and analyze other important aspects of water availability.

1. Water Availability On Year to Year Basis

   Since the flow of the rivers in Pakistan is highly erratic, it is also necessary to examine the water availability position on an year to year basis, to see for how many years water is available to meet the existing requirements/ commitments.

   The existing requirements/ commitments as as under:

   		MAF
   a.	Water Accord Allocation (excluding civil canals of NWFP)	114.4
   	(Below Rim Stations)
   b.	System Losses (annual)(Post Tarbella WAPDA figures 1977- 1994)	14.7
   c.	India's authorized uses on western rivers	4.8
   d.	Out flow to sea (Water Accord figure)	10.0
   Total		143.9

   The above quantity has been available for 25 out of 72 years during the recorded history from 1922-1994. The availability percentage is 35.

2. Kharif Water Availability

   It is also important to analyze the availability of water during Kharif season, because floods occur in this season and surplus water can become available for storage. The Kharif commitments (Post Water Accord) are as under:

   		MAF
   a.	Water Accord Kharif Allocations	77.3
   b.	Outflow to Sea	10.0
   c.	System Loses (WAPDA figures)	15.5
   d.	Authorized uses of India on western rivers (75% of annual 4.8 MAF)	3.6
   Total without storages		106.4
   e.	Requirement of existing storages	15.0
   Total with existing storages		121.4
   f.	Requirement of Kalabagh Dam(6.1 storage + 4.0 additional losses)	10.1
   Total Requirement including Kalabagh Dam		131.5

   The quantity of 106.4 MAF without storages is available for 53 out of 73 years i.e. 74% of the time. The quantity of 121.4 MAF (Kharif requirements with present storages) is available for 24 out of 72 years (1922-94) i.e. only 33% of the time. Thus enough water is not available for even filling the existing dams. If the requirements of Kalabagh Dam are also included, the required quantity of 131.5 MAF is available for just 12 years out of 72 years i.e. only 16% of the time. This position clearly indicates that any future storage can be possible only in the shape of a carry over dam, when the surplus flows of very high flood years can be stored for use in subsequent years. It may also be stated that the water can be stored only when it is available in excess of Kharif demand, because the purpose of the storage is to impound surplus water without affecting the requirement of Kharif crop.

3. Kharif Availability on Mean and 4 Out of 5 Years Basis (80% Probability)

   According to WAPDA's published figures, Kharif availability on mean year basis during the 72 years period (1922-94) was 115.9 MAF, and on 4 out of 5 year basis it was 101.8 MAF. This shows that on average year basis, there is enough water for meeting existing demand/ commitments of 106.4 MAF without storages. However, there is a shortfall of 5.5 MAF in the requirement of 121.4 MAF for filling existing storages. This deficit goes up to 15.6 MAF if requirements of Kalabagh Dam are included. On 4 out of 5 year basis, the water is not sufficient even for existing commitments excluding dams and there is no water whatsoever available even for filling the existing dams.