This week, I am looking at the Hadejia-Nguru Floodplain, and at the value of maintaining floodplain use. The Hadejia Jama’ river basin is located in North Eastern Nigeria, and includes a floodplain formed by the Hadejia and Jama river converging to form the Yobe river, which drains into Lake Chad (Thompson,1995). The river basin’s climate is dominated by the ITCZ which drives variability of rain flow, leading to periods of flooding and drought. This floodplain provides a variety of positive benefits for local communities including agriculture, resources for grazing, fuelwood, forest products and fishing(Barbier,2003).
Figure 1- Hadejia-Nguru (Muhammed,2013)
Irrigation Project Potential?
There have been several large-scale irrigation projects aimed at limiting flooding and increasing irrigation upstream. The most significant of these is the Kano River Irrigation Project (“KRIP”), which supplies water from the Toga dam to Nigeria’s second-largest city, Kano. However, 20 years after its completion only 45% of the proposed 27,000ha of additional irrigated land have been added (Thompson,1995). Projects such as the Hadejia River Project have added a further 8000 ha of irrigated land, through the construction of the Challawa Gorge dam (Barbier,2010). These projects have been associated with a rise in the water table, and consequential over-irrigation, and over-saturation of the soil with minerals leading to degradation. Further, a large part of the irrigation potential of these projects is lost through evapotranspiration and because the canals are not lined(Kimmage,2019).The adverse impact on agricultural potential downstream has been significant. It has been suggested that local government officials were bribed to greenlight these schemes, with some suspicion about the level of support for the Kafin Ziki dam(Pearce,1995)!
Figure 2- Picture of Hadejia Nguru wetland (Birdlife,2020)
Implementation of these large-scale irrigation projects has reduced the maximum area of the floodplain in the Hadejia Jama’ river basin from 300,000ha to 100,000 ha over the last 60 years(Barbier,2014). Wetlands are essential for food production in Africa. Over 1.5 million people in this region rely on groundwater recharge through flooding for their daily drinking water and crop production. Thus, when vast areas of wetlands are no longer flooded, agricultural production is limited. The potential of floodplains for agriculture is demonstrated by an economic cost-benefit analysis of the KRIP dams. The net values of agriculture, fishing and fuel wood downstream was said to have been USD 34 to USD 51 ha (Thomspon,1998). This is said to have been almost completely lost by damming (KRIP) the river, which has only added USD20-31ha to land value upstream.
In the Hadejia Nguru wetlands there are three forms of crop irrigation to utilize the wetlands’ potential: ditch irrigation, shadoof irrigation and pump irrigation (Kimmage,1992) . Ditch irrigation is the creation of embankments trapping floodwater within mini storage systems which can be used to irrigate crops in the dry season. Shadoofs and, more recently, small petrol powered pumps are new sources of water.In 1987, Diyam (unpublished) suggested that the use of small petrol pumps could increase the irrigation potential of the wetlands by 19,000ha, increasing the cropped area by 10%(Adams,1990) . Small-scale irrigation projects such as these have increased in popularity with world development organisations because of the high social and economic cost of constructing dams. Barbier et al (1998) advocate that in many places large-scale infrastructure projects do not make economic sense. They advocate for a regulated flooding regime in the Hadejia Nguru wetland area, to protect the floodplain against the harmful impact of dams downstream. Such a regulated approach could save over $5million of agricultural revenue annually. Further, economic analysis on dams in this region has not taken into account the cost of resettlement and the impact of invasive alien plant species.
Encroachment
Local encroachment of alien plant species such as Typha has caused further harm to fish and biodiversity in the downstream floodplain. Over the last fifty years Typha, for which the prime growing conditions occur at low water height (below 0.8m), has proliferated and now covers up 35,000 acres of the Mamal channel and Nguru Luke (within the wetlands) (Zungum,2019). Typha grass outcompetes other farmed crops and also reduces light penetration in water, causing oxygen depletion through eutrophication. This impacts local birdlife and aquatic organisms, and reduces fish volume and therefore fishing viability/profit(Balarabe,2013). Further, the negative impact on birdlife may harm lucrative tourism. Encroachment of alien plant species is said to cost Nigeria in excess of over 50 million US dollar per year (Zungum,2019)!
Migration
Most dramatic has been the reduction in water proliferation downstream from large-scale water projects. Since the 1960s Lake Chad’s surface area has reduced by 90%, leading to the migration of more than 2.6 million people since 2013 (Pearce,2017). Irrigation projects have caused significant harm to crop production, fishing potential and timber wood production in the Hadejia-Nguru wetlands, which cannot be replaced by the gains made through large scale infrastructure projects. For this reason, global development organisations are now focussing on small-scale irrigation projects such as petrol powered pumps as they look to the future.
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