Central Rift Valley (CRV): Threats and opportunities

BY GETACHEW MINAS

 Central Rift Valley (CRV) consists of a chain of lakes, streams and wetlands. The most common lakes in this valley are Ziway, Abiyata, Langano and Shalla. These lakes consist of freshwaters and their watersheds support the livelihoods of millions of people. The lakes deliver water for municipal, domestic and livestock consumption.

Some of these are sources of water for irrigation of farmlands. Water may be freely used from the lakes, with no user charges. Tamiru revealed that this may be due to the fact that all water resources are the “common” property of people and state. The lake waters are also sources of fish.

Large number of people, both in cooperatives and individually, depend on these lakes for their livelihoods. Women and children are also involved in processing and selling fish. According to Vuik, besides their economic and livelihood values, the lakes and their watersheds support unique ecological and hydrological characteristics.

They contain fresh water, which mainly originates from the inward rivers and rainfall. Most of these rivers are constant rivers. However, some of the lakes show a slight reduction in size in the last three decades, as a result of uncontrolled water uses for small-scale irrigation schemes in the upper catchment areas.

These are also known mostly for their large sizes and islands. They may be drained by the rivers which outflow from the lakes. Besides fisheries, they supply water for towns and irrigation for nearby floriculture farms. Yet, the levels of these lakes are not controlled.

As studies indicated, the surface areas of lakes are reduced from time to time. The annual fluctuations of the water levels of these lakes are reported to be larger, but occurring infrequently. Due to the sedimentation, irrigation and diversion of water from the main “feeder” rivers the level of the lakes has reduced over the past few decades. However, after an adjustment made for the sediment deposited in the lakes, annual water levels of the lakes are still decreasing.

The change in temperature and “precipitation” has a significant impact on the volume of inflow of water into the lakes. Studies indicate that the total annual inflow into the lakes might decline which leads to the drop of the level of lakes, shrinking the water surface area. The runoffs are likely to decrease in the future, becoming “insufficient” to meet future demands for water by the ever-increasing size of population.

Threats to these lakes include certain types of motor pumps being used to draw water from the lakes. Overfishing is also a threat to the lakes. However, the major threats of these lakes are natural factors, including climate change that could alter the ecosystem causing undesirable long-term effects.

Deforestation and farming along the lake shores destroy the buffer zones. Legesse et al reported that land degradation in the watersheds induced large scale sedimentation. The critical threats include siltation, water reduction, overfishing and release of pollutants into the lake systems.

According to Hayal, the expansion of small-scale farms and large-scale investment projects, mainly floriculture industries and irrigation farms have “reduced” the quality of water. The subsequent intensive and unintended applications of agrochemicals, untreated waste discharge, and poor watershed management practices are deteriorating the quality of the lakes. Moreover, recent development of public and private construction works in the watersheds reduced the quantity and quality of water.

There are major threats. The free use of water from the lakes and their feeder rivers enhanced unlimited use of the resource. The reduction of the lake water levels could also have resulted from siltation and deforestation in the upper watersheds. These activities are damaging the lakes, their feeder rivers and watershed resources.

They also affect both the volume of water in the lakes and their fish production. Consequently, the wetland vegetation around the lakes is depleted due to shoreline farming. The major changes that have occurred in land use and management in the lakes watershed over the past decades have reduced the volume of water.

The establishment and expansion of floriculture industries and other investment projects have discharged different pollutants into the lakes. Also, high population growth and consequent expansion of settlements and cultivated lands have caused problems to land use types, such as forestlands and woodlands. High applications of agrochemical inputs (pesticides, fertilizers, herbicides) to increase productivity have damaged soil nutrients.

Soil erosion and unabated deforestation practices for fuel-wood, charcoal and farming have caused havoc to the woodland and forests. Over-exploitation of wetland resources is now a major threat in several wetland areas of Ethiopia.

There is extensive exploitation of the fishery resource of the lakes. This is due to the excessive exploitation of resources that lead in some cases to a direct collapse of the wetland itself. An excessive water “withdrawal” is believed to be a major cause for the collapse of the lakes even though siltation also has played its part.

The depth and volume of the lakes are reduced from time to time due to intensive exploitation. Water consumption for domestic use and smaller irrigation schemes extracted millions of cubic meter of water from the lakes. The annual water extraction for soda production from the lakes is done through an artificial evaporation. Some lakes have sensitivity to changes in the river basins and any diversion of rivers for irrigation projects affects the volume of water in these lakes. The areas of the lakes are decreasing from time to time due to different factors as indicated earlier.

The gains of the lakes during rainy seasons are insufficient compared to the losses. There is a considerable reduction in the volume of the lakes amounting to about half of their present volume. In general, the levels of the lakes fluctuate according to the precipitation trends in the highlands.

Nevertheless, the recent drastic decline in level and the increase in salinity coincide with the time of large-scale water use. The current and future uncontrolled water use will have obvious repercussions, which are thought to bring serious consequences to the environment. Changes in the lakes should be perceived jointly with the use of water for irrigation around the lakes.

The evaporation of saline and salt water negatively affects the levels of lakes. Artificial evaporation of the water basins currently affects fishery activity. The declining amount and the saline-alkaline nature of water in the lakes threaten the amount of fish in the lakes. The production of soda ash, mentioned earlier, applies the technique of “solar” evaporation of salt-water from the lakes.

The nature of these lakes is such that they react more rapidly to an abrupt shift to wetter conditions than to dry conditions. These affect the production of soda ash which has not taken place because of the significant decline in the water level. The fluctuation of the lakes follows the same trend, with delays and reductions in the level of water.

These lakes experience only small seasonal water level variations. They have also low lake-bed sedimentation with high water content. These lakes have drastic changes in surface area, which may have long lasting negative impacts. The use of water and large groundwater flow from springs are factors against the relative stability of lake levels.

Tourism is a high-profile industry at the lakes and its effects are not clearly known yet. The sandy beaches on the lake shores attract tourists. Studies show that without a “control” system in place, increasing resorts and growing numbers of tourists can have negative effects on the lakes in the long term.

It is also important to consider the encroaching of the CRV. Lakes in the CRV are generally separated by an elevated strip of land, which is part of the depression edge.

The lakes are in deep saline depression with independent sub-basins of their own, and catchment areas. A “park” was developed to protect biodiversity and large number of very important birds which use the lakes as feeding, nesting and breeding grounds. The lakes are important breeding places and maintenance stations for white pelicans.

However, these sanctuaries of birds are threatened by limited interest in some of the lake waters because of their “alkaline” nature. Also, the water levels and surface areas of the lakes and the status of the park are deteriorating. Moreover, human encroachment, cattle grazing, uncontrolled use of water and other activities are threats to the lakes of CRV.

In conclusion, long-term draining of Central Rift Valley (CRV) for agricultural purposes interferes with the ecological recovery of the wetland system that is drying up faster. Many areas of wetland have been lost due to the increase of irrigation practice. Consequently, Ethiopia has lost many of wetlands in the irrigated areas. Overgrazing near the CRV lakes of Ethiopia has also contributed to the deterioration of the valley. Wetlands are also affected by pastoralists during the dry season. Overgrazing is also a threat to and affects ecological recovery period of the wetland which implies loss of biodiversity. Compaction of the wetland has also an impact on the infiltration capacity of the soil thereby affecting the hydrological system and balance of the wetland itself.

The negative effects of deforestation, siltation and soil erosion in CRV are immense demanding the immediate attention of the concerned agency. It is said time and again that “a stich in time saves nine,” reminding us of the need for quick action before it is too late for CRV to recuperate and save lives in its environ.

The Ethiopian Herald February 11/2021