In over-subscribed water systems across the globe, water managers must devise ways to meet future needs in every sector out of a fixed endowment of water and its storage and delivery infrastructure. Global climate change is one driver for developing new water storage as runoff patterns become more intense and compressed. Conjunctive management of surface and groundwater resources is a tool that can help meet this considerable challenge. Because it utilizes existing infrastructure, conjunctive management is faster and less costly to implement than other water supply augmentation strategies. Indeed, it could generate more new water supply than any other current alternative, and, uniquely, do so without any governmental subsidies.
Within NHI’s project portfolio, conjunctive management is a common strategy that is employed to augment water supply, for the reasons stated above. In the eleven regulated tributaries of the Central Valley of California, NHI is developing a system-wide roadmap to show how reoperating existing reservoirs in conjunction with storing a larger fraction of peak flows in groundwater banks could generate surplus water to restore more natural flow patterns in this immense and complicated water system. This is by far the largest ecosystem restoration program ever undertaken in this geography, while also satisfying growing demand from agricultural and urban users.
Under the system-wide approach, the storage and release regime of the Central Valley tributaries’ eleven existing terminal reservoirs would be modified to capture a larger fraction of peak-flow events as they move through the system. Additional storage capacity would be created by moving a substantial portion of the reservoir water into groundwater banks in basins with currently unutilized storage capacity. Thus, reservoir reoperation would provide source water to actively recharge groundwater banks with water that would otherwise spill for flood control. In drier years, the banked water would be recovered and reintegrated into the existing (or enhanced) water delivery system to provide supply benefits throughout the system. Enhanced storage in the terminal reservoirs creates operational flexibility that allows the surplus peak-flow water to be released into the downstream river system in a pattern that restores more natural fluvial and geomorphic processes for aquatic habitats. This management technique will substantially improve the capacity of existing infrastructure to control flood events.
The Central Valley system-wide analysis has progressed through the “proof of concept” stage and NHI is applying the results in a regional demonstration project in California’s Sacramento Valley, and as the foundation for international water management projects within NHI’s Global Dam Reoperation Initiative, including the Rio Grande-Rio Bravo on the U.S. Mexico border, the Chao Praya in Southeast Asia, the Yellow River in China and the Hadejia Nguru in Nigeria.
The Sacramento Valley - The first regional component is being developed in the Sacramento Valley in collaboration with the Glenn Colusa Irrigation District, the Northern California Water Authority and local water managers. In the context of a basin-wide integrated water management plan, we are exploring options for linking the largest federal Central Valley Project reservoir (Lake Shasta) and the State Water Project reservoir (Lake Oroville) with the local groundwater system to produce additional firm water supplies. In this case, conjunctive management holds the promise of improving supply reliability, eliminating risk factors associated with increasing groundwater use, restoring aquatic habitats in the Sacramento and Feather River basins, and buffering effects of climate change. The project is funded by the United States Bureau of Reclamation and the California Department of Water Resources.
Rio Grande-Rio Bravo Basin – NHI, the University of Texas, Austin, the United States Geological Survey, WWF-Mexico, Universidad Autonoma de Ciudad Juarez, and Instituto Mexicano de Tecnologica del Agua are trying to improve water management in the Rio Grande Basin – from the headwaters of the Rio Conchos in the Mexican state of Chihuahua to the confluence with the Rio Grande. The river is one of the most environmentally degraded rivers in North America, described by former U.S. Interior Secretary Bruce Babbitt as a "water system in crisis." Together, the bi-national team is examining the hydro-physical opportunities for expanding beneficial uses of the fixed and highly variable water supply in the Rio Grande Basin to better address an array of possible water management objectives, including satisfying currently unmet consumptive and environmental water needs. The project is designed to be a comprehensive, outcome-neutral, model-based planning exercise that will illuminate the potential for reducing future conflicts over water throughout the entire basin.
Chao Praya River – After experiencing horrific floods in 2011, improvements in flood management are the highest priority in the water resources planning arena for the Chao Praya basin. NHI and the Thai Department of Water Resources are set to examine the potential for enhancing flood control in the Chao Praya through reoperation of Bhumibol and Sirikit reservoirs in conjunction with the groundwater system underlying the command areas for the irrigation projects that are supplied by those reservoirs, and through reconnecting the river to its floodplain for transient floodplain storage. This strategy could capture a larger fraction of the peak flow events generated by the monsoon while also buffering the effects of drought periods.
The Yellow River – Ten large dams on the mainstem of the Yellow River (plus over 3100 smaller reservoirs throughout the basin with a total storage capacity of over 58 billion m3) and a levee system confines the river for almost its entire length to the sea. These dams and diversions have dramatically reduced both water and sediment flows over the past 50 years, by about 5 fold measured at the mouth of the river, and seasonal peak flows have been almost entirely lost. Until recent years, the river frequently did not reach the sea. This situation has begun to change, due to the efforts of the Yellow River Conservancy Commission, a government agency of Ministry of Water Resources of the People's Republic of China, and NHI’s partner in this project. The objective of the partnership is to explore the potential for more substantially improving the downstream environment and the fisheries in the Bohai Sea by reoperating the final reservoir, Xiaolangdi, which controls the flows to the sea. This can be done through augmenting Xiaolangdi’s storage by utilizing groundwater aquifers within some of the 100 irrigation districts served by the dam.
The Hadejia Nguru Wetlands – NHI has organized a project with local Nigerian partners to examine techniques for optimizing the irrigation systems that Tiga and Challawa dams provide to re-establish more natural flow pattern into the Hadejia-Nguru wetlands and then in the Komadugu-Yobe River into Lake Chad. The Hadejia-Nguru wetlands are an exceptionally productive area in northern Nigeria that are home to over one million people, and over 10 million inhabitants of the Hadejia-Jama’are-Komadugu-Yobe Basin are heavily reliant upon the wetlands for flood-recessional agriculture, grazing and fishing (IUCN Water Audit Inception Report, 2005). Tiga and Challawa Gorge dams control 80% of the flows into the Hadejia-Nguru wetlands. The proposed project would illuminate the technically and economically feasible options for improved operations of these two dams. The objective is to make environmental flow releases a permanent operational feature without reallocating water from economic to environmental uses, and inculcate better and more coordinated performance by the many management agencies in the basin.