XXIX-B8, 2012
affected area (Km)
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6.14-15.92
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6.14-15.92
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7-8
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HYDROLOGIC MODELLING OF KATSINA-ALA RIVER BASIN: AN EMERGING
SCENARIO FROM LAKE NYOS THREAT
J. O. Akinyede (Executive Director *); R. Babamaaji (Scientific Officer **); M. Vaatough (Scientific Officer **); K. A. Adepoju (Scientific
Officer *)
* African Regional Centre for Space Science and Technology Education in English (ARCSSTE-E),
Obafemi Awolowo University (OAU) Campus, Ile-Ife, Nigeria
*** National Space Research and Development Agency (NASRDA, Abuja, Nigeria
Commission VIII/1
KEYWORDS: Crater, Hydrologic, vulnerability, simulations, mitigation
ABSTRACT:
Understanding the hydrologic system surrounding crater lakes is of great importance for prevention of flooding damages, conservation of
ecological environment, and assessment of socio-economic impact of dam failure on the civilians in the downstream regions. Lake Nyos is
a crater lake formed by volcanic activities at the Oku volcanic field on the Cameroon Volcanic Line. It is a freshwater lake with a maximum
depth of 200 meter. In 1986, a limnic eruption at the lake emitted 1.6 million tonnes of carbon dioxide from the bottom of saturated water
into the air and suffocated up to 1,800 people and 3,500 livestock at nearby villages. The lake waters are held in place by a natural dam
composed of loosely consolidated volcanic rock, which is now at the verge of collapse due to accelerated erosion. This study was carried
out to determine the flood risks and vulnerability of population and infrastructure along Katsina-Ala drainage basins. The project integrated
both satellite images and field datasets into a hydrologic model for Katsina-Ala River Basin and its vicinity including the Lake Nyos.
ArcHydro was used to construct a hydrologic database as *data models' and MIKE SHE was employed to conduct hydrologic simulations.
Vulnerable infrastructures, population and socio-economic activities were identified to assist the Federal and State governments in disaster
mitigation and management plans. The result of the project provides comprehensive knowledge of hydrologic system of Katsina-Ala
drainage basin to mitigate potential future disasters from a potential dam failure and manage water resources against such disasters.
1.0 INTRODUCTION
Dam collapse is one of the most common disaster phenomena,
causing considerable personal injury and property damage.
Problems related to dam failures, flooding and vulnerability of
populations have greatly increased in recent decades due to
several factors including changes in land-use in the hinterlands,
urbanization of flood-prone sites, squatter settlements and sub-
standard constructions, and increased household density (Kling
et al, 1987, Smith, 2001). Lake Nyos is one of the three lakes in
the world that have carbon dioxide dissolved in their waters and
are condensed in the lower chambers of the lakes. The lake water
is held in place by a natural dam composing of loosely
consolidated volcanic rock. The waters of Lake Nyos were up
turned in 1986 expelling the gases into the air killing over 1700
and 3000 people and livestock respectively (Freeth and Kay,
1987). According to a recent study, the dam is at the verge of
collapse due to accelerated erosion. This may lead to the release
of about 50 million cubic meters of water with a consequence of
severe flooding and flood disaster along the populated plains of
Katsina-Ala River in Nigeria.
This paper provides background information on the hazards and
potential danger posed by the lake and the collapse of its dam on
the population, infrastructures, agricultural/cultural resources,
socio-economic activities and other environmental consequences
in the area. Reports and observations during the field work were
presented. Recommendations were made on how authorities in
both Nigeria and Cameroun Republics can jointly handle the
looming catastrophes with the lake and other trans-boundary
resources in the area using GIS based hydrological models.
2.0 DISASTERS ASSOCIATED WITH THE
PREVIOUS ERUPTION
Over the years, there have been a number of recorded cases of
landslides and flood disasters in the Lake Nyos region with the
worst disaster occuring on 12th August, 1986. The waters of the
Lake Nyos were up turned expelling a large volume of toxic gas
carbon dioxide (CO2) gas into the air. About 1700 people within
25km radius of the lake mostly rural villagers as well as 3500
livestocks were affected. About 845 people were hospitalised;
about 4000 inhabitants fled the area, many of these developed
respiratory problems, lesions and paralysis as a result of the
gases. The bodies of the people that died were generally devoid
of trauma. Most victims appeared to have fallen asleep and died
from asphyxiation. Properties and social amenities such as roads,
buildings were also destroyed. (Freeth and Kay, 1987; Tazieff
1989; Shanklin 1988; Kusakabe et al, 1989). About 10.000-
20.000 people were affected over an area of 300 km2 (Baxter
and Kapila, 1989). The affected area was declared a disaster zone
and more than 4,430 displaced survivors were later resettled in
seven camps constructed shortly after the disaster (Kling et al.,
1987)
Because CO, is 1.5 times the density of air, and makes only
0.394 of natural air, the gaseous air hugged the ground surface
and descended down valleys along the north side of the crater.
This deadly cloud was 50m thick and advanced down slope at a
speed of 20-50km per hour. This deadly mist persisted in a
concentrated form over a distance of 25km, bringing death to the
villages of Nyos, Kam, Cha, and Subum.
Risks related to floods and landslides in this region vary
periodically. Moreover, during certain years when the area is
