In the 1960’s, a new breakthrough occurred when River Tana cut through the protective sand dunes in the central area of the delta and created an outlet to the ocean at Shekiko. This part of the delta now consists of a network of tidal creeks, with extensive mangrove cover, interspersed with seasonally flooded grassland dotted with palms and acacia. Some of the creeks have been cut off from River Tana, but Matolo, the most western creek, has still a functional connection to the main river course (Bennun and Njoroge, 1999). Within the last 30 years, two significant events have occurred, which now control the Tana River channel above Garsen. These were: 1. The construction of the first stage of the Tana Rice Irrigation Scheme, which included construction of new water intakes and a new channel - the ‘dug river’, and, 2. Construction of the new Garsen Road Bridge over the River Tana, together with the raising of the Garsen-Witu Road on an embankment across the floodplain. The main consequence of both activities is that River Tana can no longer migrate freely across the floodplain above Garsen. Instead, it is confined to a westerly channel by the Idsowe bridge. This has led to the gradual buildup of the river bed and levees to the point where the river is almost two metres above adjacent land levels. A marked gradient now exists from west to east, between the current river channel, which lies at around 15 m asl, to the course of the former Lango la Simba which is at 10m asl. This was described by Ecosystems Ltd in 1983 as a high potential risk for a disastrous flood, and the conditions have worsened since. 2.9.2 Significant Flood Events in Tana Delta There is clear evidence, based on local knowledge, that the frequency of shallow annual floods has declined since the seven forks cascade scheme was constructed, and a double annual flood event is now rare. However, major floods still occur in the Delta and the frequency may be increasing with the onset of climate change. Floods are essential to the maintenance of livelihoods in the Delta but they also cause widespread damage and pose a threat to life of animals and humans. 2.9.3 Irrigation Schemes Although deltas are highly dynamic environments it is possible to modify their character by realigning and canalizing rivers. The history of engineering work in the Tana Delta contains many examples of schemes that have failed due to exceptional force of flood events. The record of development within the Lower Tana River and Tana Delta over the last 60 years is a litany of poorly planned engineering and irrigation schemes based on 19
inadequate data with inadequate scientific knowledge, misleading economic evaluations, a disregard for human welfare and management failures and incompetence. This situation has to change. The first major irrigation schemes were introduced in the Tana River Basin between 1960 and the early 1980s. Initially, it was anticipated that the basin had a potential of 132,000 ha for irrigation. However, due to a combination of poor design and management, and serious flood damage, many of the schemes failed. 2.9.4 Water Demand 2.9.4.1 Irrigation In 2000, the total water demand in the Tana River Basin was estimated to be 268 million m3 per year, representing 6% of the annual flow (Government of Kenya, 2012). However, if all the irrigation schemes constructed by 2000 had been operating to their full design potential, total water abstraction from River Tana would have been equivalent to about 20% of its annual discharge and this level of development could not have been sustained with the amount of storage in the catchment. Vision 2030, Kenya’s long term development blue print for the future, has set a target to increase the area under irrigation and drainage from 140,000ha to 300,000ha with priority to food production, industrial and fodder crops in the commercial and semi-commercial sectors (Government of Kenya, 2007). The present irrigation area in the Tana catchment is nominally 64,425ha, which is 45% of the land under irrigation nationally. It consists of both small and large scale irrigation. Most small scale irrigation is practised in the upper and middle reaches of the Tana by individual farmers although there are two large schemes; the Mwea Irrigation and lower Tana basin schemes which are under the control of the National Irrigation Board and TARDA (Government of Kenya, 2012). The river and its floodplain provide opportunities for cultivation in the Lower Tana Basin, mostly through flood recession and limited traditional irrigation. Some limited river fishing occurs mainly focused on ox-bow lakes which are flooded and replenished during the seasonal river floods. Lower Tana irrigation schemes faced many management and water supply constraints in the early 90s but are now being revived. New management structures are being put in place and rehabilitation is in progress although many commentators remain critical of the rate of progress and lack of capacity. 2.9.4.2 Hydropower Electricity generated from hydro-power stations constitutes more than 60% of Kenya’s total electricity TANA RIVER DELTA STRATEGIC ENVIRONMENT ASSESSMENT 2014