Location: Imo State derives its name from Imo River, which takes its course from the Okigwe/Awka upland. It lies within latitudes 4°45'N and 7°15'N, and longitude 6°50'E and 7°25'E. It occupies the area between the lower River Niger and the upper and middle Imo River.
Imo State is bounded on the east by Abia State, on the west by the River Niger and Delta State; and on the north byAnambra State, while Rivers State lies to the south. Imo State cov ers an area of about 5,100sq km.
Relief and Drainage: Imo State is underlain by the Benin Formation of coastal plain sands. This formation, which is of late
State House of Assembly Complex, Owerri
Tertiary age, is rather deep, porous, infertile and highly leached. In some areas like Okigwe, impermeable layers of clay occur near the surface, while in other areas, the soil consists of lateritic material under a superficial layer of finegrained sand.
Rivers are few with vast inter fluves which are characterised by dry valleys that carry surface drainage in periods of high rainfall. The phenomenal monotony of the terrain may be accounted for by the absence of any tectonic disturbances and by the homogeneity of the rock structure (Udo, 1970).
The main streams draining the state are Imo, Otamiri, Njaba and Ulasi rivers, all of which have very few tributaries. With the exception of Imo River, which runs through the area underlain by the Imo Shales, other rivers rise within the coastal plain sands. Generally, river valleys constitute the major physical features, which are often marshy.
The undulating nature of the interfluves gives rise to numerous depressions especially in the northeast Rainfall distribution is bimodal, with peaks in July and September and a twoweek break in August. The rainy season begins in March and lasts till October or early November. From March to May, there are violent storms which destroy crops and houses. Rainfall is often at its maximum at night and during the early morning hours.
However, vari ations occur in rainfall amount from year to year. Annual rainfall varies from 1,990 mm to 2,200. Temperatures are similar all over the state. The hottest months are January to March, with the mean annual temperature above 20°C. The influ ence of the harmattan lasts for about nine weeks (i.e. from late December to late February).
Federal University of Technology, Owerri
Imo State has an average annual relative humidity of 75 per cent which is highest during the rainy season, when it rises to about 90 per cent. The high tem perature and humidity experienced in the state favour luxuriant plant growth, which ideally should produce the climax vegetation of the tropical rain forest.
Economic trees like the iroko, mahogany, obeche, gmelina, bamboo, rubber and oil palm pre dominate. But due to high population density, most of the state has been so farmed and degraded that the original vegetation has disappeared. Thus farm ers are forced into marginal lands, a situation aggravated by the rising demand for fuelwood. Deforestation has triggered off acute soil erosion especially in the Okigwe Orlu axis.