survey of the irrigation potential of the lower tana river basin kenya

-33-
The synthetic and real data for gauging stations were then adjusted to take
account of water already allocated for future demands in the upper catchment) and thus
to estimate the .long-term availability of water at the damsites under consideration
(see Chapter Hi). -Allowanoe for potential upper catchment demands, as reserved by
the Water Apportionment Board, amounting to 338)000 acre-feet annually, has been
considered in the.computation of net flow records. This volume,which is in addition
to those authorizations granted prior to September 1956*, and for which an allowance
of 44,000 acre-feet annually has been estimated, is in accordance with the revised
authorizations issued by the Chief Hydraulic Engineer, in'October 1964.
Latterly, it has been found, as discussed in Chapter XII,that the value of
water from the upper catohment to the proposed downstream power and irrigation
developments is sufficient to justify further review of the needs for these upstream
allocations. While no formal review has, aB yet, been made, informal disoussions
have been held with the appropriate Ministries. It is understood that the projected
upstream development upon whioh the present reservations were based is no longer
considered valid and that a substantial portion of the allocations may be released
for downstream uses« Based upon present usage and foreseeable commitments, this
may be up to 400 oubic feet per second»
Some indication is given, therefore, in Chapters XI, XII and XIII of the value
and additional development of power and irrigation whioh would accrue through
reduction of upstream allocation reserves by 284,000 acre-feet annually.
Adjustment of the flow records to represent discharges at the various damsites
under review in these chapters was undertaken from intermediate tributary flow records,
insofar as this vas possible, and from general considerations of rainfall distribution
where tributary data was inadequate. The estimated net monthly volumes contained in
Annex A-l in Technical Report Volume II are considered to be sufficiently reliable
for the present evaluation of the various projeots.
To indicate the magnitudes of these flows and their distribution over the year,
Table 4-1 gives the average figures for monthly and annual flows available at two
sites, Seven Forks (Confluence; and Koreh, over the years 1937 to 1962«
Seven Forks
(Confluence)
Koreh
Table 4-1 - Net Discharges at Seven Forks.(Confluence) and at Koreh
(thousands of acre-feet)
J F M A M J J A S 0 S D Tear
82
200
44
129
51
132
237
467
411
634
209
357
121
226
107
212
88
166
129
243
263
547
143
347
1,885
3,660