Storing Water Naturally in Montana
Valerie Kurth, Member of the MWCC Water Committee and Water Resource Planner for the Montana Department of Natural Resources
“Never does nature say one thing and wisdom say another.” – Juvenal, The Sixteen Satires
One of the most interesting – and most innovative – recommendations in Montana’s State Water Plan (2015) is to explore the use of natural storage and retention to benefit water supplies and ecosystems. But what does natural storage mean, and how can we accomplish it in Montana? DNRC Water Planners recently released a short information paper that addresses these questions and more.
Traditionally, water storage has meant reservoirs, which are usually confined by human-made dam structures. Montana has over 64,000 reservoirs, and most of them are small and privately-owned (more information on dams in Montana). Demand for water in Montana continues to grow, but the likelihood of building new, large-scale reservoirs is slim because these types of projects are expensive, few suitable locations exist, and environmental impacts would need to be mitigated.
So, in the absence of additional reservoir storage, how can we continue to meet the increasing water demand? One option is to promote nature’s intrinsic ability to store water.
Riparian areas, floodplains, wetlands, and even agricultural land can act like a natural sponge. During spring run-off, they absorb water, which is then slowly released back into the channel over the summer months. This short-term, alluvial aquifer storage serves a key function: the returning water helps maintain river and stream flows late into the summer, when aquatic organisms – and people – need it the most. This type of natural storage is simple and inexpensive, as long as the ecosystem is intact (i.e., the channel can access the floodplain and the floodplain is stabilized by the roots of native vegetation).
We can also enhance the volume of naturally stored water using one or more of the following approaches:
- Floodplain restoration – Keeping rivers and adjacent riparian areas healthy and functional is the easiest approach, but it is not always possible. If the integrity of a river is already compromised, then it can be restored by reconnecting the floodplain, planting riparian vegetation, and allowing the channel to move dynamically. All of this will promote shallow, temporary storage of water in adjacent floodplains.
- Irrigation infrastructure – Seepage from irrigation canals and flood irrigation recharges shallow alluvial aquifers to supply late-season flows. Irrigation infrastructure already exists in many places, and it may be feasible to run water through it during spring runoff. However, restrictions on the time period of diversion may limit the practicality of this strategy in Montana.
- Wetlands and infiltration galleries – Unallocated water could be diverted into constructed wetlands or retention basins. Beaver dams and their artificially constructed analogs may hold the key to creating and maintaining wetlands as natural storage systems. Check out the real world examples highlighted in the Big Hole Watershed Committee’s new video, Holding Back the Snowpack.
Natural and nature-based solutions are gaining traction around the country as effective solutions to reducing the risks of weather- and climate-based hazards, especially storm-related flooding (more information here and here). Many of the same strategies for mitigating flood waters, such as preserving wetlands and keeping riparian areas intact, also function in natural water storage. Importantly, these solutions usually bring additional benefits: conserving bird habitat, protecting drinking water, and enhancing recreational opportunities are all ecological bonuses. And, when looking at the bottom line, nature-based solutions are typically more cost-effective than heavily engineered approaches (like dams) because they do not require ongoing maintenance.