Drainage Rights Dr. Matt Helmers Assistant Professor and Extension Agricultural Engineer Department of Agricultural and Biosystems Engineering Iowa State University
Drainage Rights • Drainage is necessary for crop production in many areas of Iowa • Landowners are sensitive to practices that have potential to negatively impact drainage on their land
Drainage Rights and the IOWA CREP Program • Technical advisory committee established to assist and advise the Iowa CREP on technical issues related to design and locations of wetlands to protect rights of individuals and Drainage Districts
Technical Issues Specifically related to Drainage Rights • Vertical separation between tile line invert and normal water level of wetland • Maintain drainage rights of upstream landowners • Backwater surcharging of tile lines outside of the CREP easement area • Wetland outlet/inlet designs for wetlands inside the tile zone • Design standards to preserve rights of future drainage district improvements
Technical Issues with Iowa CREP Wetland Design • Vertical separation between a tile line invert and the normal water level of wetland or low flow water level of a channel • 1 foot separation adequate for tile outlets • Limit principal spillway design for storm stage event to 3.5 feet or less where auxiliary spillway is provided
Technical Issues with Iowa CREP Wetland Design • Backwater surcharging tile lines outside of the CREP easement area: • Committee concurred that no adverse effects would result to existing tile on adjacent property if the guidelines detailed in vertical separation are followed. • Easements would be offered to the adjacent landowner under these circumstances, but would not stop the project from moving forward, provided adjacent landowner still consents to the project.
Technical Issues with Iowa CREP Wetland Design • Wetland outlet/inlet designs for wetlands in the tile zone: • Recommend gravity flow designs with language “Not more than 100% of gravity flow when downstream data is known, unless other information exists that prescribes some process to protect drainage rights”. • For drawdown structures, install orifice that limits outflow to 75% of tile capacity (Q) along with an approved management plan that allows for drawdown not sooner than 7 days following rain events greater than 2”. • Consider modified inlet protectors to lesson the build up of debris.
Technical Issues with Iowa CREP Wetland Design • Design standards to preserve rights of future drainage improvements within the watershed: • Shall allow for future drainage improvements to the most distant area, or lowest area, or the combination of both, that potentially may be drained by limiting normal wetland pool elevation such that a vertical difference of one foot for the outlet overfall, plus 0.001 grade from the pool to the potential new outlet, plus four feet for tile depth at the potential area to be drained.
Watershed Area County Road Constructed Wetland Intake Berm Outlet Structure PROFILE Road Hydraulic grade line OUTLET STRUCTURE DESIGN CONSIDERATIONS