Water from Small Dams

If the answers to the questions listed in section 2.2 suggest that the building of a dammay be technically and economically feasible, then the next questions are:• Will the project have any major impact on the environment?• What will the impact of the project be on local people and how are they involvedin its planning and management?• Does the project address issues which affect the roles and work of men andwomen in the community (gender issues)?• Are there any laws, cultural or ownership issues associated with the project whichneed to be addressed?2.11 Environmental impactBefore constructing a dam, the environmental impact must be evaluated. Small earthdams do not have a major impact, except if many small dams are constructed in thesame catchment, in which case their combined effect could be significant. The impactcan be both negative and positive. If the negative impacts exceed the positive impacts,the dam should not be constructed. The list below can be used as a checklist.Positive impacts of earth dams and ponds1. Irrigating fields and tree nurseries forgenerating income and re-planting forests2. Watering livestock near villages saves timeand reduces erosion caused by cattle.3. Providing domestic water from a hand-dugwell generates income and can lead to healthimprovements.4. Raising ducks, geese and fish farming forfood and income.5. Making bricks and construction works forincome generation.6. Reducing water-borne diseases by providingimproved water supply for domestic use.7. Saving peoples' time by reduced walkingdistances to fetch water.8. Reduced impact of floods by storing initialfloodwaters thus lessening erosion.9. Raising the water table downstream of pondsand dams which benefit well levels for handdugwells and trees.10. Increasing the value of land near an earthdam, because of all the above benefits.11. Reducing poverty levels through the incomegeneratingactivitiesNegative impacts of earth dams and ponds1. Loss of some land taken up by the damreservoir and its spillway(s).2. Risk of increased cases of malaria (this can bereduced by fish such as Tilapia Nilotica).3. Risk of increased cases of bilharzia, cholera,dysentery and typhoid (this can be reduced ifthe reservoir is fenced and the water is drawnfrom hand-dug wells or draw-off pipessituated downstream of dam walls, if drinkingwater is boiled and if people do not bathe in,and wash clothes in the reservoirs).4. Increased soil erosion along roads due topeople and animals coming for water at thedam.5. Risk of dam wall collapse if poorly designedor constructed incorrectly, thereby releasing aviolent flash-flood damaging everything in itspath.6. Siltation of dam reservoirs will shorten thelifetime of dams unless proper soilconservation is implemented in the catchmentareas.7. Risk of people and animals drowning if theytry to bathe in or swim across a dam reservoir.8. Impact on downstream users who may bedeprived of water or subject to pollution13