North Dakota



Purpose Need and ImprovementThe existing storm sewer adjacent to the west interchange of Valley City (BCBS office, former Miller Motors, 20/20 Auto Sales) appears to have reached the end of its design life. The pipe is approximately 600 feet long and consists of 9’ diameter, 8’ diameter, and 7’ diameter corrugated metal pipe getting smaller going downstream. The drainage area consists of two drainage basins totaling 12,000 acres coming from the south and west of Valley City.The pipe was installed in the 1960’s filling an existing drainage channel that paralleled I-94. This channel was located between I-94 and the I-94 Business Loop, but conveyed drainage from I-94 right of way and back to I-94 right of way. The private landowner installed a pipe that paralleled the I-94 Business Loop and then turned south to the I-94 right of way. At the time, the private landowner was notified that the pipe being installed was undersized and all future maintenance would be the responsibility of the private land owner.Staff from the City of Valley City videoed the storm sewer in September of 2015. The inspection showed that multiple types of corrugated metal pipe were used. The best pipe appeared to be the 9’ diameter pipe, with some buckling at the invert near the end section. The 8’ diameter pipe appeared to have a smaller corrugation and rusting of the joints was visible. The 7’ diameter pipe was in extremely poor condition with severe rusting at the rivets, out of round (squashed), and bulges in the walls.Hydraulic AnalysisThe existing drainage basin consists of 12,000 acres of primarily agricultural use. Small portions of the basin are utilized for roads, acreages, and rural uses. The design flows for this basin are listed below. The culvert upstream from this area is a 9’ diameter pipe with an approximate capacity of 773 cfs or roughly the 25-year event. The existing culvert which reduces in size from 9’ to 8’ to 7’ has an approximate capacity of 436 cfs or roughly the 10-year event.Design FrequencyFlow2-year90 cfs10-year429 cfs15-year551 cfs25-year719 cfs50-year975 cfsSection 89-14-01-03 of the North Dakota Century Code delineates the design frequency of storm sewer systems. This system acts as a culvert which would require a design frequency of 25 years for a Regional Road. If the system was determined to be a storm drain system that requirement would be the 10-year frequency.Proposed ImprovementsThe project would consist of investigating and analyzing alternatives to address the existing pipe system in place to convey this large drainage area through the Interstate 94 corridor. The analysis will consist of various conveying options, including alignments and material types for use in water passage. A figure has been provided with two potential alternatives for the consultant’s reference as a starting point. ................
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