30/04/2017
UNDER UTILIZATION OF THE EXISTING EARTH DAMS IN KANO STATE
By Engr. Suleiman Sani, FNSE
Abstract
Due to the climatic and geological conditions of Kano state, water for domestic and agricultural use is becoming a serious issue especially during the long dry season in the state. Although there exist 15 small and medium earth dams constructed at various locations within the state for the purposes of water supply and irrigated agriculture, the infrastructure required for their full utilizations are lacking. As a result, their intended benefits of supplying water to the vast available irrigable lands is yet to be achieved after over 25 years of their existence. Only the communities living nearby the dams are benefiting from the stored water which otherwise was designed to cover the needs of many other towns and villages downstream. This paper therefore is aimed at highlighting the untapped benefits of these dams in irrigated agriculture which could have gone along away in solving unemployment in the rural areas, arresting the current trend of rural to urban migration, increase food and cash crop production and economical empowerment of the people of the state.
Introduction
Kano state, established in 1968, has an estimated population of about 12 million. The state lies in the extreme north of Nigeria on the fringes of the Sahara consisting of a gently undulating plain sloping to the north-east. The whole state is geologically underlain by the basement rock complex where groundwater exists only in faults and major cracks within the rock. Kano state tends to have a long dry season which extends from mid October to late May, thus making the pattern and amount of rainfall in the following wet season critical if the expected crop production is to be attained. When the normal pattern and amount of rain does not materialize then there is hardship.
Construction of Dams
Due to the climatic condition mentioned above and the fact that the whole state lies on the basement rock complex the large amounts of water required for domestic use and dry season farming could only be impounded by dams. As a result over 20 earth dams were constructed under the First Kano State Water Resources Master Plan, between 1974 and 1980, for the purpose of supplying water for domestic and agricultural use within the old Kano state (including Jigawa state) by the then Water Authority (Water Resources and Engineering Construction Agency, WRECA) using direct labour. Out these dams 15 exist in the present Kano state. As a result of many changes in government with consequent changes in priorities, most of these dams are not put to their intended uses. They are rather left unattended without routine maintenance and this resulted in serious deterioration of their structures to the extent that some of them breached at one time causing damages to settlements downstream. Although a number of them are being used for regional water supply but the water treatment plants constructed are still the pilot types of smaller capacities than the intended conventional ones that are meant for their full utilization.
Beside Tiga, Watari and Tomas dams that have irrigation infrastructures, all others are without any conventional irrigation system. Although construction of irrigation system was started in 1998 by the defunct Petroleum (special) Trust Fund at Gari dam, it remains uncompleted to date due to change in government. The state Ministry of Water Resources, through its Irrigation department have managed to develop some hectares mostly on the upstream of the dams and in the Fadama areas on the downstream using pumping systems. While these have low capital cost to establish, they have very high cost of maintenance and only few hectares could be established using this system.
This paper attempts to analyze the irrigation potentials of the impounded water in these dams, the cost of establishing conventional irrigation systems, jobs that could be created by establishing the systems, the agricultural outputs and income that could be realized.
Analysis of Water Availability For Various Uses
The computation of water availability for various uses are done based on the average annual runoffs data of the various dams, as provided by WRECA. The capacities of the dams are not considered in this calculation because, for sustainability, the annual outflows should not be greater than the annual inflows, otherwise a situation may arise where the water available in the dams could not meet the annual requirements. The major consumption factors considered are:
1. Evaporation:
Due to the high temperatures and wind velocities being experienced in Kano state, especially during the long dry season, evaporation is considered a major deflation parameter of the impounded reservoirs. From a feasibility study for Kano River Irrigation Project (Phase I) conducted by Tahal Consultants (1992), the Tiga dam, which has a surface area of 17,800 hectares is estimated to have annual evaporation loss of about 96.40 million cubic meters. This figure is used as a factor to estimate the losses from evaporation for the other dams as.
2. Domestic Water Supply:
All the dams constructed under the first Kano state Water Resources Master Plan have the primary function of supplying water for domestic consumption. Therefore it is important to ensure that the amounts of water needed for that purpose is set aside annually. The capacities of the existing water treatment plants utilizing water from the various dams are much lower than what are required for the present and future demands of the regions. Estimated future requirements of the various regions are considered in this analysis so that any future extensions of the water schemes could not be detrimental to the established irrigation systems. Detailed analysis of the future domestic water demand has not been carried out in this paper, but it is roughly considered that the future demands of the various regions will be at least twice the production capacities of the existing water treatment plants. Although there is no existing water treatment plant at Bagauda dam, it is expected that one will need to be constructed to take care of the water demands of Bagauda Law School, Gargai, Rantan, Wak, Chiromawa, etc. The domestic water requirement considered under the Tiga dam is for the future annual requirement of the Greater Kano Water Supply of 200 million cubic meters, estimated by Parkman Consultants, while the quantity of 150 million cubic meters under the Challawa Gorge is to take care of the balance needed for the demand of the area by the year 2025.
3. Release for Downstream Users:
By law it is necessary to release some of the impounded water for the use of the communities downstream of each dam. Therefore it is considered in this paper that certain quantities should be allocated for that purpose annually. While the quantity considered under Tiga dam is as per the estimate made by Tahal Consultant in their feasibility study for the Kano River Irrigation Project (Phase I), for all other dams it is considered that 50% of the balance of the annual runoffs (after deducting the requirements for evaporation and domestic demand) should be released for downstream users.
4. Water Availability for Irrigation:
These surpluses, after deducting the quantities needed for the various purposes, could be used for irrigated agriculture at the various regions where the dams are located. A total of 744.14 million cubic meters could therefore be available for irrigation purposes in the state. Based on the following crop rotation, Tahal Consultants estimated the water requirement for flood irrigation in the Kano River Irrigation Project as 17,850 m3/ha.
Dry Season Wet Season
Wheat - 40% Rice - 20%
Maize - 20% Groundnut - 20%
Pulses - 10% Maize & Sorgum – 25%
Vegetables - 20% Cowpeas - 5%
Therefore, using the above estimated water requirement per hectare, it may be estimated that a total of 41,688.24 hectares could be irrigated with the total surplus water in the dams. But from data obtained from the Irrigation Department of the Kano state Ministry of Water Resources and the Kano River Irrigation Project only about 18,070 hectares of irrigation lands are developed. This means a balance of 23,618.24 hectares of irrigation land remains undeveloped in the state.
From the writers personal experience it is estimated that 5 adults could be fully employed throughout the year on one hectare of irrigable land. Which means that a total of 118,091 adults could have employment if the balance of the potential irrigation land is developed. Also based on the Tahal Consultants estimates of expected agricultural output per hectare of 2.5 metric tons, 59,059.59 metric tons of food and cash crops could be produced if these lands are developed. This could have yielded an annual gross income of N1,113,068,383.82 to the farmers, that is after deducting the cost of inputs.
Conclusion
From the analysis above it may be seen that Kano, as a result of the first Government’s foresight of harnessing the available water resources in the state, is blessed with water bodies strategically located and ready for use in domestic and agricultural activities. But unfortunately successive governments derailed from the master plan of utilizations of the impounded reservoirs prepared by the first government, as a result of which about 23,618 hectares (representing about 57%) of the proposed irrigation lands remained undeveloped. This would otherwise have provided employment to about 118,090 citizens, increase the state’s annual agricultural output by about 59,045 metric tons and increase annual domestic income from agriculture by about Naira 1.11 billion.
Reference:
1. Ministry of Water Resources Kano State, 2006: Irrigation Project Areas in Kano State.
2. Tahal Consultants Limited, 1992: Feasibility Study for Kano River Irrigation Project (Phase 1) Extension.
3. Water Resources and Engineering Construction Agency (WRECA) Kano State, 1980: Main Project Data of Dams & Reservoirs.
4. Water Resources and Engineering Construction Agency (WRECA) Kano State, 1982: Hydrological Year Book 1971 - 1972
