Climate change is affecting watershed hydrology across Minnesota, resulting in an increased need for and interest in water storage. Changes in precipitation patterns, land use and other landscape factors, including surface and sub-surface drainage, have resulted in a loss of surface storage and modification of subsurface water storage. Historical large-scale wetland drainage, loss of native vegetation, and changes in the mix of crops have combined to reduce short-term and long-term storage. Loss of storage can result in reduced evapotranspiration, higher peak flows, increased annual runoff, flashier stream flows, accelerated channel erosion, and/or increased risks of flood damage.
Water storage can take many forms, from storage in the soil profile to natural (or constructed) depressions like wetlands, or constructed storage basins. Different storage practices affect the runoff from the watershed in different ways. Constructed storage practices such as ponds or wetlands will slow down runoff and reduce the peak flow from a watershed, but these types of projects typically do not change the overall volume of runoff. Other practices such as land use changes or improvements in soil health will promote additional infiltration and reduce the overall runoff volume from a watershed, but typically do not reduce the peak runoff rate the way that structural practices do.
In 2021, the Minnesota Legislature directed BWSR to establish a water storage assistance program (Minn. Laws 2021, 1st Special Session, Chap. 6, art. 2, sec. 80 (Minn. Stats. §103F.05)):
"The board must establish a program to provide financial assistance to local units of government to control water volume and rates to protect infrastructure, improve water quality and related public benefits, and mitigate climate change impacts."
The legislation also defines the practices considered as “water quality and storage practices”:
(d) "Water quality and storage practices" means those practices that sustain or improve water quality via surface water rate and volume and ecological management, including but not limited to:
- retention structures and basins;
- acquisition of flowage rights;
- soil and substrate infiltration;
- wetland restoration, creation, or enhancement;
- channel restoration or enhancement; and
- floodplain restoration or enhancement.
Based on this legislative directive, BWSR has established a pilot grant program: Water Quality and Storage Program Grants, to support storage practices in the Minnesota River basin and the Lower Mississippi River basin in Minnesota. Eligible practices must control water rates and/or volumes to protect infrastructure, improve water quality and related public benefits, and mitigate climate change impacts. Given the current funding levels, this program is being established as a pilot that will provide funds for design and construction of storage projects.
The need for water storage is highlighted in the Natural and Working Lands section of the draft Climate Action Framework.
The draft paper, “Water Storage: A Planning and Decision Framework,” was developed by an interagency team under the direction of the Minnesota Climate Subcabinet. Two of the Subcabinet action teams, “Natural and Working Lands” and “Resiliency and Adaptation,” identified the need for an overview of water storage opportunities and resources. This paper is being made available as a resource for local governments considering water storage projects under the pilot grant program or as part of their watershed planning efforts.