The Tiga Dam is located on River Kano, 70km south of Kano City.  It is one of the largest dams in the country and was designed and built between 1970 & 1974.  This Dam is the cornerstone of water resources development in the Kano River Valley in Kano State and Hadejia River Valley in Jigawa State.  The Dam sustains irrigated agriculture for thousands of hectares in Kano River Irrigation Project, Phase I and Hadejia Valley Irrigation Project, Phase I, currently being developed.

By releasing water from the dam during both rainy and dry seasons of every year, thousands of farmers along the river course, from Kano to Hadejia and beyond, grow variety of crops for both cash and food.  The Dam is also another source of drinking water for Kano Metropolis, other towns and villages along the river course in Kano, Jigawa, Yobe and parts of Borno States.

Tiga Dam is part of the programme of water resources and agricultural development contemplated in the “Feasibility Study of the Chad Basin” conducted by the United States Bereau For Reclamation in the early 1960’s.  The programme includes the construction of Challawa Gorge Dam on a tributary of River Kano in Kano State (completed 1992), and the Kafin Zaki Dam on River Jama’are in Bauchi State and the development of irrigation projects such as Kano River Projects I & II and the Hadejia Valley Projects I & II.

FEATURES OF THE DAM

The Tiga Dam has the following features:

Type of Dam – Zoned Earth fill

Crest Length – 6,000m

Structural Height – 48m

Hydraulic Height – 42.68m

Maximum Base Width – 274.30m

Total Storage Capacity – 1,974mil.m³

Active Storage Capacity – 1,845mil.m³

Surface Area of Reservoir – 18,900 hectares

Total Vol. Of fill Material – 9.18mil.m³

Spillway Type – Free Overflow Concr. Ogee (457m)

Emergency Spillway Width – 200m

The Dam is equipped with three outlets as follows:

1. The main outlet is a 3.65mÆconduit supplying a 2.2mÆ Howell Bunger regulating valve.
2. 90cmÆconduits with 60cm regulating valve.

The main Dam outlet, comprising of bulkhead gates, butterfly valve, etc, is installed in the outlet valve chamber, which is submerged 16 meters below the full supply level.

OPERATION AND MAINTENANCE OF THE DAM

In 1976, the Authority took over the responsibility of the dam i.e. operations and maintenance.  With time, and due to some inadequacies in the original design and the construction of the dam, some signs of distress were observed in 1978, 1984 and 1986.  These were apparent despite routine maintenance and monitoring that were being carried out regularly.

In 1986, the Authority, in conjunction with Federal Department of Water Resources, invited the Nigerian Sub-committee on Dams and experts from the United States Bureau for Reclamation to inspect the dam and advice on what should be done to save it against possible collapse.  The two organizations aforementioned carried out some exercise and submitted their reports to the Authority in 1987.  The reports strongly save the Dam.  Some of these measures are:-

A. IMMEDIATE MEASURES

1. Construction of an emergency spillway to relieve the dam embankment from excessive hydrostatic pressure

1. Cleaning and clearing of the toe drains of the dam to include extending its length to cover more distance at the foot of the dam downstream.

• Cleaning, clearing and repairing the inspection chambers of the toe drain.

1. Excavating the cracks observed on the dam crest, and backfilling after carrying out measurements.
2. Stabilisation of the downstream slopes
3. Grassing of the downstream slope and placing of rip-rap and repairs on the upstream slope

• Provision of adequate free board for the dam
• Repairing the existing hydro-mechanical equipment installed long ago

1. Similar other repair works and maintenance

B. LONG TERM MEASURES

1. Complete cross-sectional surveys to determine the in-situ position of the dam embankment and to establish Geodetic Triangular for the dam.

1. Instrumentation of the dam

• Overhauling of the hydromechanical equipment in the outlet chamber

1. Carrying out of Geotechnical investigation of the dam and its foundations
2. Provision of Radio Communication and security installations
3. Some additional engineering tasks such as field observation for the capacity of the additional spillway, hydrological investigation, analysis of embankment pressure distribution, slope stability analysis and development of “Dam Safety Monitoring”.

DETAILS OF PROGRESS ON REPAIRS AND MAINTENANCE

1. An emergency spillway was constructed on the left hand side of the dam, 200m wide and 3.50m lower than the existing dam
2. The hydromechanical equpment in the dam have been inspected and are planned to be overhauled with the gallery already cleared and cleaned, awaiting funds to repair it to its integrity level.

3. The downstream slopes of the dam are protected as follows:
   1. Filling of deep gullies in the embankment with over 600,000meter cube of soil and about 74,000meter cube of stone aggregate
   2. 30,000sq.meter of grassing in the downstream face
   3. About 1000-meter cube of lump stones have placed in the upstream slope to protect it.
   4. About 2km of toe laying about 300 lengths of 225m x 10 bars x 6m uPVC-perforated pipes in graded aggregate and washed sand has rehabilitated drain.

4. Provision and installation of piezometers and settlement pins have been completed.
5. The dam site has now been provided with radio link (communication gadget) for effective monitoring
6. Security has been installed at the entrance of the dam to ensure effective protection against trespassing and possible vandalism.
7. The dam embankment has been rid of rodents and termites that might endanger its safety and integrity.

The items enumerated above needed money to execute and in early 1988 the Authority sent a memorandum to the Federal Military Government requesting funding.  In March 1990 Federal Government came to the aid of this valuable investment by approving releases of funds to effect repairs on the dam and some of its appurtenances.

Presently, the repairs and rehabilitation of the dam and its appurtenances have been completed since 1992.  The hydromechanical equipment over-hauling and replacement of parts and gallery have also been effected.

With the completion of the remedial works on Tiga Dam and the construction of Challawa Gorge Dam there would be enough water for envisaged projects downstream to Lake Chad.  However, it has been observed that the conveyance deficiency of the river system is very low due to heavy losses which can be minimized by river training, channelization, construction head works in addition to hydro-geological investigation.

• Kano River Project, Phase I (15,000ha. of land complete with all headworks and field structures).