Highway Drainage Impact Reviews
State law requires that a property owner, land developer, or public entity obtain written permission from the State before constructing or reconstructing a driveway or public street or road to a state highway, or before making any improvements or alterations to land or drainage features adjoining the highway by grading, filling, subdividing, platting, land leveling, driveway construction or other comparable activities that may impact the drainage facilities of a state highway. (See Neb. Rev. Stat. §§ 39-1360, 39-1359, 39-1361, 39-1362, and 39-1332 to 39-1335.) The activities described above, including work that would have a similar impact, will be referred to herein as construction or alteration work.
Plans for the proposed construction or alteration work must be provided to State for review along with a full drainage impact study completed by an engineer with training and experience in hydraulic and hydrologic engineering.
Review of a drainage study and construction or alteration work plans by the State does not relieve the applicant of the applicant’s sole responsibility to properly and accurately design and construct its improvements and to meet all applicable federal, state or local requirements. Further, the applicant will be solely responsible for any damages to private or public property caused by applicant’s improvements or alterations.
Rules for Construction or Alteration Work
Applicant’s construction or alteration work:
(a) Must not divert drainage water, directly or indirectly, from its natural or long established drainage basin, path or course. Drainage waters must not be directed toward State property from areas that do not presently drain to the right-of-way by natural contours or under long-established existing drainage paths.
(b) Must not allow drainage waters to overtop or flow onto or along the highway from adjoining roads, streets, or lots. Storm sewers must be used to keep driveway, road or street surface drainage from flowing onto the state highway surface.
(c) Must be designed and constructed so that post-development discharge rates onto State property do not exceed pre-development discharge rates.
(d) Must provide appropriate stormwater detention located off of State property to mitigate any increase in peak discharge onto State property.
(e) Must not cause drainage waters to back-up, pond-on or erode as those waters enter, cross or exit State property.
(f) Must not create a new drainage ditch or path onto, across or parallel to the highway.
(g) Must not increase the velocity of drainage water entering State property. Applicant may be required to install appropriate erosion control to protect State property.
(h) Must not change drainage in a way that will make State’s existing drainage facilities non-conforming with NDOR standards and policies.
(i) Must not connect culverts on private property directly with State’s drainage culverts, except in extraordinary situations with written approval from State.
The Drainage Impact Study
The following applies to Applicant’s drainage impact study:
(j) The calculation of expected peak flows discharging from the proposed development site for existing or pre-developed conditions, must use the appropriate design storm (return period) for that highway (i.e., Interstate-50 yrs., Expressways-50 yrs. …, etc).
(k) The study must identify all existing drainage conditions, including delineation of drainage areas that contribute storm runoff to the applicable drainage facilities located on highway right-of-way. Applicant may not divert additional drainage waters to the highway right-of-way.
(l) Peak discharge calculations must be completed using the NRCS curve number hydrology method to develop the inflow hydrograph and the Storage-Indication (modified Puls) Method for storage routing. NDOR does not accept the Modified Rational Method for the design of stormwater detention facilities.