Repairing checkdams

June 17, 2019 admin

Here are some photos of the huge effort in Yam Makaa to repair the damage caused by the extra heavy rain in late April (Eija’s and Ric’s neigbours from Moshi measured over 30 cm of rain that one night and over 160 cm the following night).

It looks like that this project became mainly a building experiment on how to control a gully by checkdams rather than just building the dams. The soil in the area is extremely erodible. When it is dry it is like fine chocolate powder or a hard packed crackable block. In the rainy season streams, rivers and gullies flood with thick brown water like hot chocolate.

 

Erick, the lawyer in the village took the lead in thinking through all the main FAO building instructions that we wanted to follow and discussing the lessons learned from the broken dams with Eija by WhatsApp. Then he worked with Ndanu and four helpers from the village to repair the dams.

We decided that yes, 1. we do want to try to follow the instructions and build sloping edge gabions to guide the water off the fragile gully side. This instructions was not acceptable to the builder who led the wrok earlier. 2. We had learned now that the gabions need to be embedded to the sides of the gully for about a meter (we had followed 50cm rule from the FAO instructions). 3. Spillway needed to be built deeper than before. 4. We needed better ways to guide the water off the edges on the upstream side so that it would not get between the gabion and the soil of the gully edge. Ndanu and Erick decided to fill sacks by soil and load them on the edges side by side. 5. Embedding the gabions to the sides of the gully need to be done more precisely and avoid breaking the sides, otherwise water finds its way between the gabions and the sides of the gully.

So the two upper dams (5 and 4) were rebuilt. Water had already widened the gully during the rainy season, so more gabions and stones were needed. But we decided not to buy more materials. We had exhausted the budget for this task. So they emptied some gabions from checkdam 3 and carried the stones by Erick’s car to repair dam 4.

Now we need to wait till the rainy season of April-May next year to see how they last.

The first photo shows how an additional one-meter gabion is inserted at the side of the foundation layer to enforce the bottom layer.

Sloping gabions from the sides and sacks piled up on the up-stream side corners.

A big thank you to all those who put this huge effort to try again! That’s the only way we will learn.

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