Yemeni dams and their opportunity costs [Archives:2006/1006/Health]

December 11 2006

Dr. Gerhard Lichtenthaeler
The village children had waited eagerly for the onset of the rainy season. When the floods finally arrived during August 2006, the newly constructed dam filled rapidly.

Mohammed and many of the village boys were pleased because the dam presented a wonderful opportunity to splash in the water. “Al-hamdulillah, no accidents have happened yet,” Salih remarked.

Like many of the area's farmers, he put high hopes in the small dam, which took nearly two years to complete. “It really is strange,” he says, “Those with wells just downstream and in the area of the dam haven't noticed any recharge yet. But a few well owners from other villages several kilometers away report that the drop in groundwater levels has slowed.”

During a November 2006 site visit, only a few small portable petrol pumps were pumping water from the dam to irrigate the surrounding fields. “Why aren't more farmers utilizing the water?” I asked. “Most of us have our own well, so there's no need,” Salih replied.

Having been completed in 2005, the dam in question was empty in July 2006 when photographed. Following the 2006 summer rainy season, the dam (measuring 120 x 60 x 3 meters deep) contained approximately 20,000 cubic meters on Oct. 17 (see photo).

To locals from the nearby village, the 2006 rains were good and in their perception, the dam had filled to promising levels.

In comparison to the 20,000 cubic meters of water in the dam after the main rainy season in 2006, a single pump in the same basin can pump approximately three times as much groundwater per year, or approximately 60,000 cubic meters. This figure is based on a well yield of six liters per second, pumping 12 hours a day and a total of 240 days per year during growing seasons.

Granted that irrigation efficiency measures provide water savings of 30 percent or more, the same amount of water that was stored in the dam could be saved annually by a single pump, which usually irrigates up to five hectares of land. According to a recent well assessment for 2006, the agricultural plain where the dam is constructed has 1,500 wells and 2,600 wells in the basin's catchment.

While the cost to equip one pump and the land irrigated by it with a modern on-farm irrigation scheme comes to approximately US$7,000- US$10,000, the dam cost YR 89.5 million, or nearly half a million U.S. dollars.

Therefore, for the price of this small dam, 50 pumps irrigating approximately 250 hectares of land could be transformed into modern irrigation schemes, thus saving 50 times the amount of water the dam had stored at the end of the 2006 rainy season. Given that average landholdings in the basin's agricultural plain are two hectares or less, 125 farming families or more would directly benefit.

Dr. Gerhard Lichtenthaeler works for the German Development Cooperation, in support of the Ministry of Water and Environment and the National Water Resources Authority. The views expressed here are his own.