Floodplain Inundation vs Irrigation

Hello all!

In my previous posts, I spoke broadly about the different types of water valuation - monetary and non-monetary. In this post, I will elaborate more on the Hadejia-Nguru Wetlands example that I spoke about previously, and highlight the usefulness of water valuation for resource management.

Continuation from previous post: Case study of the Hadejia-Nguru River Basin, Nigeria (Barbier and Thompson, 1998)

The floodplain benefits outlined previously however, have increasingly been challenged by the other large-scale water resource schemes in the region, circled in red in Figure 4. The Kano River Irrigation Project (KRIP) presently irrigates an area of 22000 hectares (Tanko, 2010), while the Hadejia Valley Project irrigates an area of 12500 hectares (Kimmage and Adams, 1992). Both of these large-scale irrigation schemes have not considered the opportunity costs arising from the reduction in flood extent to the Hadejia-Nguru wetlands further downstream, and this case study quantifies the economic benefits of the floodplains by comparing the net agricultural benefits from the large-scale irrigation projects and the net values of the agricultural, fuelwood and fishing benefits of the floodplain.

A hydrological model was developed to estimate the impacts in flood extent on the Hadejia-Nguru wetlands from the employment of various irrigation scenarios - this may be familiar to colleagues who had similarly done GEOG2020 in the previous year.  To illustrate my point, I will only utilise 2 scenarios with respect to the KRIP described in Table 3. Using the estimated overall floodplain benefits (fishing, fuelwood, agriculture) of USD34-50/ha and the estimated agricultural benefits of the KRIP of US20-31/ha, the forgone floodplain benefits from the hydrological scenarios were quantified.

Table 3. Net loss from the operation of large-scale irrigation schemes.

	Description	Regulated releases (106 m3)	Differences in mean peak flood with baseline scenario (km2)	Net loss = irrigation value – floodplain loss (in US$)
Scenario 1	Tiga dam present, not in operation.	Naturalised flow from Wudil river.	0	0
Scenario 2	Tiga dam in operation. KRIP over area of 27000ha.	None	-150.62	-3362041
Scenario 3	Tiga dam in operation. KRIP over area of 14000ha.	400 in August.	-95.25	-2203912

Using these two scenarios, it is evident that a) a reduction in production by the KRIP, and b) provision of artificial water to replenish the floodplain, would reduce the economic losses by more than a million USD. The large-scale water resource schemes were disadvantageous to the Hadejia-Nguru river basin, and the way forward to minimise losses was to follow Scenario 3, where regulated releases are still supplied to inundate the floodplain to ensure the continued viability of the wetlands.

There were three main limitations to the case study:

1. The economic benefits of Tiga dam in supplying water to Kano was not quantified, but preliminary evidence argues that it is unlikely to be substantial enough to justify the substantial floodplain losses.

2. The full economic benefits from the floodplain has not considered for pastoral grazing and groundwater recharge, although this was quantified in a study few years later to be USD413/ha of irrigated agriculture extracted from the aquifer, with the potential loss in 1m of groundwater level valued at USD62249 (Acharya and Barbier, 2000).

3. There are other costs to dam construction and operation, eg. excessive flooding of schools and villages affecting households and livelihoods downstream of the Tiga, changes in fish stocks downstream, health hazards such as waterborne diseases from ponding behind the dam and waterlogging when farmlands are excessively flooded (Idris, 2008).

Summary and Thoughts

There have been other more recent studies on ecosystem benefits valuation of wetlands (McCartney et al. 2011; Turpie et al. 2008), but I felt that this case study on the Hadejia-Nguru wetlands would be relatable to most of us due to our acquired experience with hydrological modelling (and STELLA) in the previous academic year. It might therefore serve as a useful starting point to extend our knowledge on water resources and ecosystem services. Notably however, the case study dates to two decades back. The Hadejia-Nguru wetlands have been facing longer agricultural droughts in recent years, with the northern regions of Sub-Saharan Africa facing a 11% decline in rainfall, which is further threatened by the proposal of the Kafin Zaki dam construction (Shettima, 1997). Despite the delay for a few decades now, there has been no consensus on the intentions over the dam construction. It is therefore essential, and of strong economic justification, for regulated releases of water to replenish the floodplain during wet seasons, and to alleviate instances of prolonged droughts; this recommendation comes in contrast to the full implementation and further construction of the irrigation schemes as earlier proposed.

Although I find myself convinced that economic valuation of water is indeed the most practical solution moving forward for water resource management, I have also taken a strongly economic (and perhaps, rather inhumane) approach to valuing water, along with basic economic jargon such as opportunity cost. In my upcoming posts, I hope to bring a stronger human touch when writing about water and ecosystem services, in particular addressing livelihoods and poverty in Africa, and the potential for economic valuation to address these issues.

See you next week!