Charco Dams

Materials required:

• A tape measure
• A line level
• Long strings
• Wooden pegs
• Shovel(s) and/or wheelbarrows
• Optional: Draught animals with ploughs or an excavator

Steps of Implementation:

1. 1. Dam planning

LOCATION: Using a topographic map of the land or a simple sketch, locate the position of the reservoir, inflow channels, overflow channels, the silt traps, and the embankment.

Two factors help to determine the best location for your dam: 

1. 1.  Soil type: Coarse-grained, clayey soils are best suited for Charco dams as these will retain water better than fine-grained sandy soils. 20-30% clay content is the minimum requirement. If the dam reservoir is located in an area with porous soils, consider lining it with a 20-30 cm layer of clayey soil.
   2. Topography of your land: Usually, the lowest point on the land is the most suitable place for the dam. If possible, choose a natural depression where rainwater accumulates during the rainy season. Or, choose a location close to where rainwater runoff flows naturally.

2. Excavation. 

Clear the vegetation and mark out the area:

Begin by uprooting and removing all vegetation and stones from the construction area. Next, create an outline of the structure by using wooden pegs and a long piece of string tied to the middle of the pond. Wrap the string around the pegs. Follow the proportions indicated in the picture below as much as possible but make adjustments when necessary.

Excavation of a charco dam can be done:

• Manually with shovels and wheelbarrows. (3 m3/day p.p)
• By use of draught animals with scoops, ploughs and carts (30m3/day p.p)
• In an automated manner, by hiring a excavator/bulldozer

3. Construction.

There are a number of different elements that need to be constructed to create a complete charco dam.

• The Pond
  Should be at least 3m deep in-order to make the dam worthwhile despite evaporation.  Create a slight slope from the bed (deepest part of the pond) towards the inlet. This way, when the water evaporates it may remain in the deeper sections of the dam, minimizing the surface area exposed to evaporation.
• Inflow
  If a natural channel for the water does not already exist, dig an inflow channel that will lead runoff water into the pond. The inflow of the dam should be located where rainwater usually accumulates or passes by in a stream. If needed, the size (length and width) of the inflow area can be extended to increase the water catchment capacity of the pond. 
• Earth wall
  Use the excavated earth from the pond to form an earth wall on the edges of the dam. Heap the excavated earth around the dam immediately after digging. Compaction of the heaped earth is not necessary. Build the earth wall with moderate slopage to avoid erosion: the slopes of the wall should be flatter than 1:1 or 45 degrees. Make sure that enough space is left between the edge of the pond and the heaped soil/earth wall to build the Berm. The earth wall should be highest opposite the inflow section. 
• Berm
  The Berm is an area between the reservoir and the earth wall that is  left untouched. It facilitates transportation in and out of the construction site and avoids stops earth from the wall falling back into the reservoir. If there are plans to enlarge the dam during the upcoming seasons, leave more space for the Berm than the 2m recommended in figure 1. 
• Spillways
  Spillways ensure that water flows safely and in a controlled manner over the dam wall. Two spillways beginning at the inflow and following the exterior of the earth wall should be built. One spillway on either side of the wall. Spillways for charco dams are built as small gullies paved with stone and long-rooted grass in order to avoid erosion.

Several additional, but not mandatory, features can be added to enhance the Charco dam.

• Silt traps: A series of silt traps of 1 to 2 meters deep should be excavated along and beyond the inflow channel. Silt traps should be between 5 and 20m away from the mouth of the reservoir. This helps minimizes the silt that enters the reservoir). 
• Fencing: It is best to fence off earth dams to keep livestock and unwanted people away from the dam to ensure water quality and prevent spread of diseases.
• Windbreak: Trees can be planted along the exterior of the dam wall. When planted facing the prevailing wind direction, trees can protect the dam walls from erosion and reduce evaporation. A row of vegetation can also act as a fence (cheaper option).

This intervention contributes to:

Estimated costs of intervention (in Kenyan shillings - Ksh):

Estimated benefits of intervention (in Kenyan shillings - Ksh):

Based on a case study of the annual value of benefits from a 500m3 water reservoir (Source).

1. Deployment of Charco-Dam Technology by small villages in Nzega district, Tanzania

Description
In semi-arid regions of Tanzania, farmers and cattle owners construct small earth dams called charco dams (or Milambo in Kiswahili) to mitigate water scarcity. These dams are strategically built in natural depressions where rainwater accumulates, utilizing deep clay, silt, or Black Cotton soil to minimize seepage and evaporation losses. To further reduce evaporation, trees and shrubs are planted on the windy sides of the dams to act as windbreaks. The ideal sites for charco dams are near gullies or natural waterways that can divert water into the dam during and after rains. Farmers typically dig these ponds manually, expanding them over time to increase capacity. The dam water is primarily used for livestock but can also be treated for domestic use. The design of a charco dam resembles a halved calabash, with the "handle" serving as the inflow channel and the "bowl" as the water reservoir. Logs are placed in the inflow channel to function as steps and silt traps, preventing sediment from filling the reservoir. This intervention provides a sustainable water source for agricultural and domestic purposes, enhancing resilience in semi-arid regions.

External sources 

• For more information on water from small dams, please click here
• On how to determine the clay content of your soil,, please click here.

Guides 

• For a full manual on planning, designing, constructing and maintaining ponds, pans and small dams, please click here.
• For an easily accessible guide on earth dam (charco dam) design and construction for water retentions, pond and lake creation, please click here.

Videos 

• Introduction into earth dams’ design 
• Planning of charco dam design using GIS model