These are normally constructed to contain water for production purposes such as irrigation, livestock and fish farming. 

Valley Dams / Valley Tanks, are built in natural depressions and earthen embarkment built across the valley of a drainage line to intercept and retain the water flowing down the drainage line. Soil is scooped out in an area near natural drainage line and a channel created to lead water to an excavated tank. 

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Purpose of Valley Dam / Valley Tank

Purpose of valley dam is to impound (store) water, waste water or liquid bound material for any of the several reasons such as flood control, human water supply, irrigation, live stock, recreation or pollution control. Valley Dams Valley Tanks have different designs depending on purpose for each construction.

Valley Dams / Valley Tanks for Irrigation

Design Features

Length should be longer than the width to prevent failure of open walls. 

- Edges should be slanting to prevent collapsing in of the edge walls.

- It should have an outlet to pass the excess water.

- Always recommended to prevent the tanks by facing. 

- It should have appropriate depth to reduce on evaporation losses. 

How big should the water tank be

Valley tank sizes may depend on factors like

- Volume of water required.

- Soil type.

- Field slope.

- Recharging capacity.

Excavation Methods

1. Manually excavated tanks

2. Machine excavated tanks.

Manually Excavated Tanks Advantages

- Some areas can have softer soils in this case can be cheaper. 

- Some areas have good water recharge capacities, smaller tanks can be excavated hence reducing on costs. 

- Some areas can not be accessed by machine which is not the case to people. 

Manually Excavated Tanks Disadvantages

- Some areas are hard to be excavated by people.

- Local labour takes time to mobilize and may not be consistent. 

- Local people can not make slanting edges increasing chances of wall failure. 

- Method takes much more time. 

Machine Excavated Tanks Limitations 


- Expensive

- Some areas may not be accessible to machines. 

Advantages of Valley Tanks over other artificially constructed water sources

- Can provide sufficient water to irrigate over 5 acres. 

- Cheaper compared to deep hole drilling and some swallow wells. 

- Cheaper and convenient in terms of water drawing compared to keeping water falls and pressure constant. 

- Does not need sophisticated equipment to determine areas where they can be constructed. 




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Mpereza Building

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