Existing Buthorn Drain system is shown in green with white manholes.
Buthorn Storm Water Drain – Project Summary
The Buthorn Drain has over its history evolved from a rural natural drainage channel collecting irrigation waste returns, groundwater seepage, and storm water runoff into a fully piped (limits of project study area) urban storm water and irrigation drain. This transformation, although gradual, has resulted in the Drain becoming over-charged during measurable storm water events resulting in localized flooding and associated negative impacts to private property and the public in general.
Grand Valley Drainage District (GVDD) has recognized that the Drain is over-appropriated in its function and has decided to pursue methods to remedy its lack of capacity and multi-jurisdictional management. Souder Miller and Associates (SMA) was hired in August 2016, by GVDD to undertake engineering investigation of the Drain and develop a workable preliminary design and budget for a new storm water drain to provide relief from urban storm water entering and over-charging the Drain. The overall remedy would essentially partition the Drain, leaving it to handle irrigation return flows and groundwater seepage through its open-jointed concrete piping, while providing a separate Storm Water Drain to manage urban storm water runoff.
SMA work scope has been multifaceted including detailed surveying of the Drain’s underground features from 25-1/2 Road to Patterson Road (limits of project design); overall watershed hydrology; non-storm water flow measurement in the Drain; detailed hydraulic analysis of the Drain and proposed storm water drain; cost estimating; and coordination with the City of Grand Junction, GVDD and Grand Valley Irrigation Company staffs.
The hydrologic study work identified there are two basins which contribute runoff to the Drain. The upper basin lies north of Patterson Road and extends to I-70. This is the larger of the two basins at 472-acres, and this basin can produce a peak discharge of 599-cubic feet per second (cfs) for the 100-year storm (1% chance storm event). The lower watershed is 173-acres in size, producing a peak discharge of 173-cfs for the 1% chance storm. When both basins were combined and routed to the outfall west of 25-1/2 Road, the peak discharge is 685-cfs. Note: lower basin peak flow occurs before upper basin arrives; hence, the lower combined peak flow value.
Background flow measurement in the Drain found that irrigation seepage from the upper basin is estimated at 2.75-cfs. Seepage intercepted in the Drain between the Grand Valley Irrigation Canal and 25-1/2 Road added another 4.9-cfs. These values continually fluctuate due to rainfall seepage, irrigation practices and time of year irrigation delivery operations.
SMA, utilizing its detailed survey of the Drain, Mesa County 2-foot contour interval surface mapping, and GIS data supplied by GVDD, built a hydraulic model of the Drain using software suited for urban surface and storm drain analysis. Each storm water inlet into the Drain was built into the model, as well as the runoff flows entering from the upper watershed. The initial run of the model quickly identified
the Drain was inadequate to handle storm water and irrigation flows and verified what experience has shown us.
The base model was then used to test alternate alignments, add more inlets, trial different pipe sizes and shapes, and ultimately develop an independent storm water drain scenario. Development of a preferred alternative included evaluating an in-situ enlargement of the Drain, routes down surrounding streets, and improving inlet capacity on the Drain to handle localized flows and reduce associated flooding. Other parameters considered in the analysis process include gravity utility conflicts, the cost of shutting down minor and major arterials (1st, 7th, Orchard, and Bookcliff), adequate flowline grade, and construction costs drove the alternative analysis process to the preliminary design developed by SMA.
The proposed design summary:
- New Storm Water Drain (new 9,000-foot interceptor drain),
- Open channel outfall to the east side of 25-½ Road, horizontal elliptical concrete pipe (54“x 91“)
- East side of 25- ½ Road to Lorey Drive, 72” diameter concrete pipe,
- Lorey Drive to Grand Valley Irrigation Canal, 4’ x 10’ concrete box culvert,
- Add inlets along new Drain alignment,
- Install two (2) siphons on GVIC delivery system.
- Remove old concrete pipe from Outfall to west side of Bass Street,
- Install new 36” concrete pipe in the old pipe location,
- Siphon under new Storm Water Drain (optional) four (4) locations,
- Add area inlet at Orchard and 1st Street.
The proposed Storm Water Drain’s design has been broken down into three phases to allow flexibility in its implementation. Based upon funding and resources it can be broken down into smaller phases, although the cost to design and mobilize for more phases will increase the cost to construct.
The preliminary design and supporting opinion of probable costs (OPCC) present a challenging and complex project to construct. Major street intersection closures, as well as disruption to neighborhood traffic and construction noise, will result. These are the unavoidable realities of such a project in an urban environment.
The end product will provide a long-term robust solution for the City of Grand Junction and GVDD allowing both to meet their obligations for irrigation return flow and storm water management