As has been confirmed in Ethiopia the Vetiver System has a great capacity to recharge groundwater – how does this work? Why does Vetiver do this better than other species?
Vetiver enables significant ground water recharge because:
(1) the stiff dense Vetiver hedgerow when planted on the contour spreads out rainfall runoff behind the hedgerow before allowing the runoff to proceed downslope. Often the hedgerow creates a back pond of 2 meters or more upslope from the hedge.
(2) Because the hedgerow spreads out water, the water when passing through the hedgerow moves evenly to the downslope area thus enhancing soil infiltration over the whole downslope area.
(3) Vetiver’s unique, dense and deep root system will penetrate deep and through plow and other hardpans, thus opening the way for rainfall infiltration to the groundwater table. Because the crown of the Vetiver plant is so dense rainfall runoff moves very slowly through the hedgerow thus allowing time for the infiltration process
Other grasses cannot compete with these characteristics of Vetiver, in particular its hedge density and rooting characteristics. Addition most are badly effected by drought, fire and over grazing, whereas Vetiver is not.
NOTE: good inter-hedgerow cultivation practices, such as minimum tillage further enhances runoff reduction.
Research results mostly show that Vetiver hedgerows are superior to comparative biological systems. Note that these experiments are carried out on standard runoff plots that do not reflect the reality of microcatchments where rainfall is most often concentrated into defined flow channels of high velocity flows. In addition many of the experiments are one or perhaps at the most two year trials, and do not take account of vetiver’s phenomenal ability to hedge up and become denser over time.
Engineered terraces and other conservation structures generally divert precious water off the land into waterways that more than often become gullies. They do not enhance rain water infiltration as they do not have the capacity to break trough hardpans or create improved infiltration. Additionally they take up a lot of land and harbor weeds and rodents, and are costly to maintain.
Further Vetiver hedgerows can mitigate catastrophic rainfall events as was shown so well in Honduras when Hurricane Mitch hit that country. Farms with vetiver hedgerows were fully protected (Texas A&M).