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The Ecological Impacts of Ilisu Dam on Tigris River Basin in Iraq

As an engineer, I admit that the traditional engineering that we have learned for decades and which is still taught in our universities has created many complex problems in human life. One of these problems is the large dams. It is time to turn to the principles of sustainable engineering which has successful solutions to many of the current problems our civilization is facing).

(This article was prepared in 2005, a year before starting construction of Ilisu dam)

Khalid M. Shaheen

Of the facts in environmental science and engineering is that God has created the universe on miraculous accurate system.. The Earth as a part of this vast universe follows the rules of this wonderful system. All physical, chemical and biological systems on and in earth are on a trend of marvelous harmony. Then came the man to disturb this wonderful harmony, leaving cases of chaos that himself with all his advanced technology are now unable to restore things to their original balance.

Surface water resources are one of the natural systems that have been manipulated by human beings in order to adapt them to their desires. Dams are one of the facilities that disturbed the balance of water resources. In as much as dams have benefits, they have, in the same time, serious damage that sometimes outweighs their benefits.

The negative effects of water impoundment projects vary in number and type. Among these effects is the change in morphology of rivers and coastal delta, the impact on the hydrology and vegetation of the area, the change in the pattern of distribution of sediment loads and siltation, the stimulation of nutrient enrichment, the change in the thermal system of the river, etc.

In the following few pages, we will attempt to briefly explain some of these effects, namely; the effect of dams on aquatic life and fisheries, the deterioration in water quality parameters, specifically the temperature and dissolved oxygen level that have significant impacts on the aquatic life in the river, the effect of water impoundment on the capability of water downstream the dam to digest the tons of pollutants discharged to it, in addition to the subject of deprivation of agricultural land of natural fertility and the consequent need to compensate it with inorganic fertilizers that are toxic.

The Anticipated Ecological Impacts of Ilisu Dam on Tigris River Basin within Iraqi Territory

It has become evident that the geographical location of dams and the natural system of rivers can provide basis for assessing the impacts of dams on the ecosystems upstream and downstream dams. However, the prediction of all such impacts remains limited and confined to the type of changes, not their quantity. In addition, the process of predicting the impacts becomes complicated as a river passes through different geological and climatic zones. When a series of successive dams are constructed on a single river basin then the problem get more complicated since it creates cumulative effects on water quality.

Knowing that the knowledge available in this regard is not sufficient to provide fixed bases for accurate and specific prediction. The following are some of the potential impacts of Ilisu dam on Tigris River basin in Iraq:

1. Disconnecting the continuity of the river upper parts with its lower parts. This discontinuity will be an obstacle to the usual migration of fish to reproduce in the high parts of the river. Although the amount of water discharged from the dam is usually adequate for the life of non-migratory fish, it is not sufficient to enable other species to migrate.

2. Settling of sediments and nutrients in the dam lake will eliminate the aquatic plants downstream the dam. This will, in turn, change the biological systems downstream the dam as a result of lack of nutrients as well as the change in the physiochemical environment.

3. Decomposition of the vegetation submerged in the water of the lake newly formed upstream the dam. Such process will release nutrients, including nitrogen and phosphorus. Add to that the settling of suspended substances and the discontinuation of the transfer of organic matter and nutrients through the dam. All these changes will increase the primary productivity of the newly formed lake with it subsequent deterioration in water quality.

4. Disappearance of different species of organisms and oppositely the predominance of other types, including water fern, which may cover the surface of the lake and prevent sun light from reaching other aquatic plants. Accordingly the process of photosynthesis and its subsequent release of oxygen to the water of the lake will be hindered, as well as the blocking of the mixing of the surface water of the lake by the action of wind. All these will enhance oxygen depletion in the lower layers of the lake. Thus, the water discharged from the bottom outlets of the dam will suffer from a deficit in dissolved oxygen which, in turn, has negative effects on the biological system and fish in the river and on its self-purification capacity as well.

5. Although the problem of dissolved oxygen deficit in the lower water layers can be mitigated as water is released through the turbines, it is believed that it will not be sufficient to overcome this problem as necessary because of the limited time the water passes through the turbines.

6. In addition to its dissolved oxygen deficit, the water released from the dam bottom outlets usually contains different concentrations of iron and manganese hydroxides, and hydrogen sulfide produced by the anaerobic decomposition processes in the lower layers of the lake.  These compounds can corrode metals and concrete that is in contact with this water.

7. Dramatic changes occur in flora, and fauna groups in the water following impoundment. To restore their original situation these biota need many years on condition that no other changes occur following water impoundment. It is natural that these changes will be transferred to the water flowing from the Ilisu dam to Iraq.

8. The aquatic organisms in the riverbed downstream the dam will be affected by the salinity of water caused by evaporation in the lake upstream the dam. Naturally this effect will be  greater in the water coming out of Mosul dam because of the more evaporation that will occur in the water that reaches Mosul dam lake after leaving Ilisu dam.

9. Spread of disease causing insects and molluscs, in addition to crustacea.

10. The temperature of the water downstream the dam generally does not compatible with the river natural system of temperature. It is therefore expected that the thermal system in Tigris river will change dramatically downstream Ilisu dam. This could extend to tens of kilometers along the river basin. In the science of ecology water temperature is an important parameter in assessing the changes caused by dams to the downstream aquatic environment. This is due to the effect of water temperature on physical, chemical and biological processes in any river. Thus, changes in river temperatures are among the most important factors affecting the chain of the aquatic organisms.

11. Thethermal stratification in the lake and the relatively high temperature of the water downstream the dam at certain times of the year will make the water flowing to Iraq suffer from a severe deficit in dissolved oxygen. The river water that suffers from the lack of oxygen has limited capability to oxidize organic substances and other pollutants discharged to it through self-purification process. Now if we look at this issue from another side it might be worse. The big reduction that will occur in the discharge of the river if accompanied by a deficit in dissolved oxygen will reduce the ability of the river to dilute the tonnage of pollutants that will be discharged to it as he passed through the successive cities of Iraq. Taking into account the probable industrial growth in Iraq in future, the river may be no more than domestic and industrial wastewater stream.

12. The quality of water discharged from a stratified lake is usually depends on the level of the outflow structures. During summer, if water is discharged from the surface of the lake, this water will be warm, nutrient-free and contain a good concentration of dissolved oxygen. On the contrary, the water discharged from the lower ports will be cold, free of dissolved oxygen and nutrient-rich.

13. Within the temperate geographical area (23.3-66.3 degrees north) where Iraq and Turkey are located, the temperature of the water discharged from the lower parts of the lake (hypoliminion) in summer is expected to be much colder than the natural river water. In winter, the temperature of this water will often be slightly higher than that of the river. Figure (1) shows a model of the expected variation in water temperatures during the different months of the year between the natural river and that of the water discharged from the lower layers of the lake.


Source: McCartney, M.P., et al.  2000   

Figure 1: A model of the expected variation in water temperature between the natural river and that of the water discharged from the lower layers of the lake.

14. In temperate regions and in some cases, the density of fish in the basin of the river downstream the dam get increased because of the heat-modified water system, the increase in plankton in water, and the low turbidity, which are preferred factors for some species of fish. This phenomenon is evident in Figure (2).


Source: McCartney, M.P., et al. 2000

Figure 2: variation in the density of fishing crop in the basin of the river

The cessation of annual floodwaters in the Tigris river basin after the completion of the Ilisu dam will deprive the floodplains downstream the dam of tons of silt. Silt is a natural fertilizer that has great impact on enriching agricultural soils and raising the pace of agricultural production. To compensate for this expected shortage in free natural fertility, Iraq should use inorganic fertilizers, at a cost of tens of millions of dollars.

The inorganic chemical fertilizers used in developing countries to improve and increase their agricultural production contribute to the growth of world agricultural production by about 40%. But at the same time, these fertilizers have a negative yield compared to natural fertility, many of which are the following:

1. Reduce the soil content of organic matter and consequently the ability of soil to retain water.

2. Reduce the soil content of the oxygen which is negatively reflected on its ability to represent the fertilizer.

3. The inorganic fertilization does not provide more than 2 or 3 of the total nutrients needed by the plant, in time plants need more than 20 types of nutrients.

4. Inorganic fertilizers consume a lot of energy to be produced, transported and applied to soil.

5. The use of inorganic fertilizers leads to the release of N2O, a greenhouse gas that causes global warming.

6. The contamination of surface water due to the reach of nutrients embedded in fertilizers through surface runoff following a rainfall event. The most important nutrients are nitrite NO3 and phosphate PO4 that lead to the spread of algae, which has bad consequences on the quality of water in the lake.

7. Rainwater infiltrated into the soil can carry with it nitrite of inorganic fertilizer into groundwater. Groundwater containing high concentrations of nitrates is toxic to infants and causes liver cancer.

References

Adams, W. “Downstream Impact of Dams”. World Commission on Dams. Jan. 2000.

Goldman, C. R. and A. J. Alexander “Limnology” McGraw-Hill Book Company Japan, Ltd. 1983.

“Human Health and Dams”. World Health Organization, Geneva, Nov. 1999.

McCartney, M.P., et al. “Ecosystem Impact of Large Dams”. World Commission on Dams, 2000.

Miller, G. T.   “Living in the Environment”, 13th ed., 2004, Thomson Learning, Inc. USA.