Erosion Control Is Everyone

Erosion Control Is Everyone’s Battle

Okenwa R. Nwosu, M.D.

Erosion is a necessity of life. The earth that we inhabit today would have been unable to support life without the fact that it has been tamed, through the eons, by the forces of erosion. Primitive hard rocks and caustic chemicals were systematically degraded over time to yield the fertile soil which supports plant life on which all other life forms subsist. Erosion is, in fact, the giver of life because without it, we would not have the fertile fields to plant crops or nutrient-rich bodies of water that sustain aquatic life on which we depend for some of our food. Over a long period of time, a given environment tends to reach a state of equilibrium where soil erosion, though present, is barely perceptible. Floodwater is the most significant erosive agent in the rain forest zone of Nigeria. The undisturbed forest usually has a thick vegetation cover of trees and associated undergrowth. The force of falling rain does not impact the soil directly because the forest floor is usually covered by decaying leaves. Elaborate root network of the forest vegetation cover profusely perforate the topsoil thereby enabling it to soak up the percolating rainwater like a giant sponge. Even during heavy downpours, little surface floodwater emanates from a mature undisturbed rain forest.

The gully erosion that is devastating the equatorial rain forest belt of Nigeria is directly caused by disturbance of the natural equilibrium that has existed in the area since prehistoric times. Human migration out of the African savanna to inhabit the equatorial rain forest initiated a set of activities that ultimately led to the upset of a delicate balance that maintained stable relationship between the land, flora and fauna of this zone. Sedentary agrarian lifestyle of new rain forest residents necessitated clearing of natural vegetative cover to make way for cultivation of food crops. Our ancestors observed the fragility of exposed topsoil and judiciously evolved cultivation methods that allowed for regeneration of vegetation cover before repeat use of a given piece of land once again. Shifting cultivation technology served our ancestors quite well. They successfully grew their staple crops and still avoided disruption of the equilibrium which kept the ample annual rainfall precipitation from washing away the valuable topsoil on which their agrarian lifestyle depended.

Population growth compelled our ancestors to further modify their methods to enable them to cope with new challenges. Having more mouths to feed meant that cultivated lands were not given enough time to fully recover before planting on them again. Besides, more of pristine forest areas were cleared for human habitation as the population grew. With an annual rainfall that averages 80 inches or more, floodwater management techniques were put in place to compensate for permanent removal of natural vegetative cover. Residential compounds, public arenas and farmlands were provided with shallow catchment pits, mud wells and designated flood channels to minimize, control and manage runoffs in ways that averted the consequences of uncontrolled erosion. Earthen dykes were built between clan and village land boundaries to ensure that floodwater effluents from contiguous territories did not constitute a nuisance to neighbors. In densely populated parts of central Alaigbo, for example, intensely cultivated farms were delimited by mud dwarf walls or hedged with trees to discourage free flow of floodwater across property boundaries. Freshwater springs that dotted the landscape of pre-colonial Nigerian rain forest zone attested to the functionality of the indigenous adaptation methodologies and environmental management skills that were devised and implemented by our ancestors.

But things began for fall apart at turn of the 20^th Century with the onset of colonial conquest and modernization of the lifestyle of indigenous peoples of Nigeria’s equatorial rain forest. Emphasis was deliberately shifted from food to cash-crop cultivation for exports to British cosmopolitan markets whose industrial base was becoming more and more reliant on produce from newly acquired territories overseas. Extensive tracks of virgin rain forest were cleared in one fell swoop to make way for establishing new palm plantations, for example. Burgeoning outside trade and quest to acquire newly introduced minted currency encouraged growth of urban settlements and thus increased the need to clear more forest areas to accommodate the emerging townships. Socioeconomic infrastructural development, such as roads, markets, schools and churches, quickly began to alter the lay of the land in far-reaching and irreversible ways. Undesirable side effects of the new way of life began to manifest in forms of gully erosion and silting of waterways in parts of Alaigbo in first quarter of the last century. Some basic efforts were made to maintain roads, both the paved and unpaved varieties, by the colonial administration. Most would agree that erosion menace was still kept at bay in most parts of the country until the Civil War and post-war era.

Many factors converged simultaneously to escalate and complicate erosion problems that are evident today in the equatorial rain forest belt of Nigeria. Census figures show that Nigeria’s population has more than doubled since the country attained independent rule 45 years ago and therefore, more land has to be cleared on continuing basis for agriculture and sundry human habitation needs. Buildings and residential compounds are much larger that they used to be. Roofs are now made of corrugated metal sheets and open spaces around buildings tend to be compacted and paved with concrete or bitumen thereby rendering them almost impermeable to rainwater. Whatever tree cover that is left is indiscriminately being cut, as we speak, to make way for erection of electric power and telephone lines. Due to poor planning, new network of roads are still being built across natural floodwater channels without adequate drainage. We now have a scenario where more floodwater runoff is generated than ever before and allowed to run wild all over the place. Unfortunately, the soil formation in most parts of the rain forest zone is of the loose lateritic type and is thus fragile and highly susceptible to floodwater erosion.

Generous rainfall, which has been a source of unique blessing for our ancestral land, has now become a source of scourge and anguish for this generation. In parts of Alaigbo, for example, valuable topsoil, which took thousands of years to buildup, have totally disappeared within only a few decades, leaving behind bare, hard and unproductive laterite that cannot support any plant life without extraordinary effort. In communities that are situated in higher elevations, building foundations are seriously undermined by floodwater erosion of the surrounding area. Unchecked rainwater runoff that originates from homesteads and farmlands converge downstream to form torrential floods that excavate the loose soil on their way, including streets and roadways. Silt and other debris carried downstream by unchecked floods are deposited in natural waterways. Former freshwater springs are disappearing and streams as well as rivulets are choked with silt and debris which render them useless as sources for clean water. Multitudes of gully erosion sites have emerged, in their thousands, where none existed in the recent past. Valuable farmlands and homesteads are being swallowed in huge gulps by these ever expanding gullies during each rainy season. River Niger and its tributaries, which used to serve as major transportation corridor only a few decades ago, are now filled with sand bars that make then hazardous for water transport.

Understanding the true pathogenesis of the erosion menace which devastates Alaigbo and other contiguous territories that comprise Nigeria’s equatorial rain forest belt is critical in devising the proper tools and procedures that must be deployed to rein in this monster before total ruination is visited on our people. As is clearly evident, the solution lies in reestablishing the delicate balance that was in place before things went haywire. There are two constants here about which we can do little to radically alter namely: the high annual rainfall and the loose soil formation. We must learn how to work with these natural factors in deriving practical solutions to the erosion menace. The strategy for containment shall be two-pronged; we must stop erosion menace on its tracks and then rehabilitate the land in ways that shall heal its current wounds and also immunize it against future recurrence of this scourge. For all practical purposes, the two issues must be addressed concurrently. The underlying principle is to make rainwater to infiltrate into the soil as close to where it falls as is humanly possible. Whatever floodwater that happens to escape this initial dragnet must be sequentially trapped and prevented from gaining access into existing gully erosion sites.

The first line of defense against erosion menace is within each homestead, farmland or open public space. The soil should be rendered as permeable as humanly possible. Trees and shrubs, both ornamental and economic ones, should be liberally planted and open spaces should be covered with grass instead of impervious pavement or compacted laterite. Shallow mud pits and wells should be constructed in the most dependent parts to receive runoff from roofs and other unprotected areas. The goal is to achieve a zero runoff from each location in question. Along paths, streets and roadways, shallow catchment pits should be placed at close enough intervals to collect floodwater from nearby elevated grounds. Excess runoff from these man-made receptacles should never be allowed to run free along the streets or roads but instead should be channeled along habitual natural flood paths which are more resistant to erosion by surface water. Large ponds or artificial lakes should be constructed at appropriate locations along flood channels to function as reservoirs for holding all excess runoff in times of increased rainfall. Again, it is very important to prevent all surface water runoff from reaching the vicinity of all existing gully erosion sites.

The best way to heal the land starts with protecting it from the elements through provision of adequate vegetation cover. Trees and grass do not only provide cover but also they help the soil to conserve its moisture content. The central role of tree planting in erosion control can never be overemphasized. Shrubs and grass cover are also helpful in shielding the topsoil thereby preventing its denudation by wind and rain. Parts of former equatorial rain forest of Nigeria have transformed into savannas with scanty tree population in spite of the fact that rainfall precipitation still remains high. In these areas, the topsoil is usually depleted by repeated cultivation, floodwater erosion or overgrazing. Some indigenous tree species, like gmelina and cashews, can still thrive in this soil type and they should be planted aggressively as a major step in inducing topsoil stabilization and eventual recovery. The vicinity of gully erosion sites should be covered with trees where possible and giant bamboos which tend to do quite well even when planted on bare edges of gully cliffs. Grazing by livestock must be avoided in threatened areas until they are rehabilitated enough to support such an activity.

Like many things in nature, time heals all wounds provided that additional insults are prevented from aggravating the situation. The menacing gullies that currently scarify our landscape can recover and heal themselves with passage of time if we take the essential step of starving them of surface floodwater influx on which they feed to grow into the monstrosities that they have become today. The battle to rein in the menace of uncontrolled erosion in Alaigbo and other parts of Nigeria’s equatorial rain forest can be won but this counteroffensive must be launched now with the right stratagems before we lose additional grounds. A sustainable and effective battle plan requires everyone’s input, from the grassroots who inhabit the blighted land to the societal leaders who control the nation’s purse strings. Individuals, groups, communities and various governmental jurisdictions have clear roles to play in building the team that can conquer the threat of erosion scourge and rehabilitate our God-given land from being the eyesore that it is today. Embarking on this battle shall mark a turning point for the rejuvenation of the domestic economy, creation of employment and inculcation of much needed maintenance culture amongst the citizenry. And most important, restoring the sanctity and integrity of our ancestral land is the boldest and clearest statement that we can ever make to the whole world about our will and ability to shore up the innate dignity of the contemporary African.

OKENWA R. NWOSU, M.D.