IRD Zimbabwe Hosts Regional Rainwater Harvesting Workshop
IRD Zimbabwe hosted the Regional Rainwater Harvesting Workshop for Southern Africa in Harare, December 5-6, 2012. Country Director Themos Ntasis convened the workshop, saying “We are not rainwater harvesting evangelists. But we do see it as one of several potential solutions to regional water needs.” Ntasis said it was important to compare this solution to others, considering the volume and quality requirements of users, level of precipitation, funds available to construct the collection system, and availability of materials and expertise. Deputy Country Director Nick Ahlers added that IRD has about seven years of experience in rainwater harvesting in Mozambique, Zimbabwe, and Swaziland. He said the workshop’s objectives were to examine rainwater harvesting applications and to compile best practices for partners to apply in future projects.
IRD demonstrated an innovative tool to the 30 participants, who came from Mozambique, South Africa, Namibia, Swaziland, Zambia, Zimbabwe, and Kenya. The tool helps IRD determine the optimal size to construct a water storage system. For example, you could design a huge tank so large that it would never fill, or a tank that would fill—but also empty—very quickly. You don’t want either of those: the first would be prohibitively expensive, and the latter wouldn’t solve your water problem.
The IRD tool uses a simulation to calculate the number of days over a year that a tank of a certain volume will be empty, and tries to minimize that number given a number of factors and assumptions. The tool runs simulations, based on assumptions about water consumption per person per day during both dry and rainy seasons, available surface area to collect water from, loss of water to the gutter systems, and daily average precipitation, among others. By changing the assumptions, you can see how the water availability would change throughout the year, which can help you determine the most advantageous size of tank to construct.
For more information about this tool, contact Themos Ntasis.