Megawatershed

"Excerpt from Robert A. Bisson, "Megawatersheds" in the "Water Encyclopedia: Groundwater", edited by Jay H. Lehr and Jack Keeley (John Wiley & Sons, Inc., Publication, 2005)

Coined by groundwater pioneer Robert A. Bisson, the term "Megawatershed" describes deep-seated subsurface aquifer systems that may consist of gravel, fracture-hosted bedrock, and/or sedimentary structures, which are integrated in terms of recharge, storage, transmissivity, and containment. They may not coincide with surface topographic divides and may receive recharge from parts of several surface watersheds including massive amounts of mountain block recharge. "Megawatershed" is a conceptual model, or paradigm, that describes this new class of groundwater domain. Bisson heads EarthWater Global, a groundwater exploration and development company based in the United States. EarthWater uses oil, gas and mineral technologies to find and develop Megawatersheds on a sustainable basis.

Background

Megawatersheds are formed over geologic time by a combination of factors, including tectonically induced brittle fracturing and displacement of rock facies and strata and solutioning of parent rock facies and regolith by chemically aggressive meteoric and hydrothermal waters. The history and nature of regional tectonic stress fields and principal bounding faults, interacting with lithology and climate, play a major role in determining the geometry and extent of megawatershed boundaries.

Megawatersheds often transcend surface topographic divides and may receive recharge from parts of several surface watersheds. Similarly, as a structurally contained water resource, wells drilled into multiple aquifers in a single megawatershed may produce water from potentially dissimilar lithologies with common hydraulics related to brittle fracturing and gravity-fed contributions from adjacent and overlying unconsolidated sediments. Megawatersheds often occupy diverse host environments exhibiting both primary (continuous) and secondary (fracture) porosities with flow systems delineated by fracture systems, faulted and/or weathered lithologic contacts, and igneous intrusions (e.g. dikes), overlying or adjoining weathered rock and overlying porous unconsolidated sediments. This model supersedes the traditional watershed and aquifer models, which describe topographically controlled, functionally two-dimensional drainages and incorrectly depict most deep groundwater resources as static, poorly recharged artifacts of surface flow, confined to local discrete bedrock or alluvial units.

The megawatershed concept operates effectively and has scientific valididty and economic and management utility on a scale of 10s to 1000s of square kilometers. Studies have documented megawatershed environments in Africa, Asia, the Middle East, Europe, North America, South America, and the Caribbean.

History of Discovery

The space age has induced quantum leaps in geologic theory, and comparable advances in geophysical instrumentation and interpretive methods have permitted scientists to discover new information about the genesis, composition, and structure of the earth's crust and the internal dynamics of the many fluids, (e.g., magma, oil, water) contained within it. Equally important, the perfecting of computer-based geographic information systems (GIS) allowed skilled explorationists to combine and analyze many different types of data quickly and accurately, leading to major discoveries of oil, gas, minerals and, more recently, to breakthroughs in the understanding the nature and extent of groundwater resources, including the discovery of complex aquifer systems coined "megawatersheds" by the explorers who first documented the phenomenon, circa 1987, in the Great Rift systems of East Africa, where mountain block recharge from mountains and highlands in Ethiopia, Sudan, Kenya, and Chad remains largely untapped.

Exploration Program

When the megawatershed paradigm is used as a groundwater exploration model, the result is greatly improved understanding of groundwater environments, permitting accurate, comprehensive assessments of "safe yield" from local, countrywide, or regional water resources. The megawatershed paradigm actually provides a template for measurement of all facets of the hydrologic cycle in reality-based natural hydrogeological catchments, including rainfall, evapotranspiration, surface and subsurface inflow and outflow interactions with surface water, shallow aquifers, deep fractured bedrock, and deep alluvial aquifers.

Modern explorationists employ current geologic theory, state-of-the-art exploration technologies, and interpretive methods adapted to the oil, gas and mineral industries but rarely used in the groundwater field. The "megawatersheds" paradigm of groundwater occurrence is the template the exploration program follows.

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EarthWater Global

At the 2008 World Water Awards, EarthWater was recognized for its groundbreaking work: “By thinking outside the box, EarthWater Global has come up with a business proposition that could change the future of water development worldwide.” [Global Water Awards http://www.globalwaterawards.com/summaries/technologyidol/ewg.php]

EarthWater's wells have little to no environmental footprint, each requiring just 1/20th of a hectare. And, unlike traditional point-source solutions, the company is able to site its wells at or near the point of demand. This is highly unusual in the water community: rarely can a country’s demographics determine sites of production. Developing countries in particular stand to benefit from a low-cost, environmentally friendly, and local solution. Increased criticism from the development community points to the expanded construction of dams and desalination plants as being expensive and harmful to the environment.

Trinidad and Tobago

In 1999, the island of Tobago was in the midst of a water crisis that threatened to deter foreign investment and curtail economic growth. The island’s 19,000 cubic meters per day (m3/day) deficit far outweighed the less than 1,900 m3/day of sustainable groundwater capacity expert hydrologists believed to be available. A costly dam in the Western Hemisphere’s oldest protected rainforest appeared to be the only viable option. Hoping to avoid a 5-10 year wait and significant environmental damage, government authorities hired EarthWater to map and develop new water resources on a Build-Transfer Contract. Within twelve months, EarthWater identified over 190,000 m3/day of Megawatershed resources, an amount 100x previous incremental groundwater estimates, and delivered 19,000 m3/day to the Island’s waterlines. EarthWater went on to discover over 950,000 m3/day on the island of Trinidad and developed 76,000 m3/day for immediate use. [Trinidad & Tobago: Long Term Development Challenges and Opportunities (Inter-American Development Bank July 2004 Report), an analysis of Bisson / Earthwater's project in Trinidad (2001) and Tobago (2002-2003) http://www.earthwaterglobal.com/docs/TrinidadTobago.pdf]

Africa

In 1984, USAID and the UN Refugee Agency called in Bisson’s team to Somalia. At the time, drought and conflict aggravated acute famine and rampant cholera, and previous efforts to develop significant quantities of groundwater in the country’s West had failed. Before the project was terminated by civil war, the team identified over 76,000 m3/day of groundwater capacity and developed wells delivering 7,600 m3/day to those in need. Three years later, USAID again hired Bisson to develop water in Sudan. And although the State Department halted the drilling of production wells after the coup d’etat in 1989, the team identified more than 38,000 m3/day of new capacity in deep bedrock fracture zones.

All in all, wells developed by EarthWater’s team currently pump in excess of 190,000 m3/day. This is just a fraction of what the company has proven to be available worldwide.

References

Robert A. Bisson, Megawatersheds in the "Water Encyclopedia: Groundwater", edited by Jay H. Lehr and Jack Keeley (John Wiley & Sons, Inc., Publication, 2005)

* http://ww.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=215858&VERSION_NUM=1&p=20 Water and Wastewater International (October, 2004)

* http://www.EarthWaterGlobal.com EarthWater Global homepage

* http://enr.construction.com/people/multimedia/podcasts/2008/080805.asp Engineering-News Record Podcast (2008)

* http://www.earthwaterglobal.com/pubs/Megawatershed%20Exploration-%20A%20State-of-the-Art%20Technique%20Integrating%20Water%20Resources.pdf Bisson, R.A., Sheffield, S. and Sisk, S., 1995, "Megawatershed Exploration: A State-of-the-Art Technique Integrating Water Resources and Environmental Management Technologies", proceedings of the IDA World Congress on Desalination and Water Sciences, Abu Dhabi, UAE. November 18-24, 1995

* http://www.earthwaterglobal.com/documents/EarthWaterENRArticle.pdf McGraw-Hill's Engineering News-Record article, "Shattered-Rock Systems Provide New Water Resources" (William Angelo; August 6th, 2008)