City Council Considers Drainage Problem Down Town
March 18, 2020
Taken directly from project summary presented by KLJ
The Town of Big Sandy has hired Kadrmas, Lee & Jackson, Inc. (KL&J) to complete this preliminary engineering report (PER) for the storm water system. This Preliminary Engineering Report (PER) documents the study, conclusions, and recommendations for the Town's storm water system facilities. The PER identifies the planning area, evaluates the existing condition and operation of the existing infrastructure, identifies existing problems within the system, and establishes a recommended course of action and design basis for storm water improvements to meet the needs of the Town, and to the extent possible, meets the requirements of State and Local storm water management practices. A summary of the project background and recommended improvements are presented in the Executive Summary.
The planning area considered in this report is centered primarily on Johannes Avenue, which is the main street of the town. Big Sandy is located in north-central Montana, approximately 34 miles southwest of Havre, Montana, and 77 miles northeast of Great Falls, Montana along U.S. Highway 87. The Town lies in Chouteau County.
Approximately 29 acres contributes storm water runoff to Johannes Avenue, referred to hereafter as Main Street. The contributing area includes commercial development, mostly along Main Street, and low to medium density residential areas. The contributing drainage basin is located mostly in the northeastern portion of town.
The foundation of the storm sewer system was laid when the Town was initially developed, and the streets were graded by residents in the early 1900's. Main street has an inverted crown cross section and has two inlets in the center of the street, one at the intersection of 1st Street and Main and the other at the intersection of 2nd Street and Main. The storm drain infrastructure is located perpendicular to Main Street along 1st Street and 2nd Street.
The northernmost inlet on Main Street is connected to approximately 130 feet of covered storm drain ditch to the northeast and 400 feet of storm drain pipe to the southwest. The storm drain pipe to the southwest transitions from 15-inch diameter corrugated steel pipe to 18-inch diameter corrugated plastic pipe at a downstream inlet. Two additional curb opening and grate inlets, located 138 feet and 224 feet downstream from the Main Street inlet, discharge storm water into this stretch of pipe.
The southernmost inlet located in the center of Main Street discharges storm water into approximately 220 feet of 15-inch diameter corrugated steel pipe along 2nd Street. Three additional circular grate inlets discharge storm water into this stretch of pipe located approximately 38, 99, 174, downstream from the Main Street inlet. Storm water is then routed through drainage ditches located along 2nd Street and Michigan Avenue, and discharged onto a field located southeast of town. A 3-foot diameter corrugated steel pipe with a headage on the discharge side conveys storm water under 5th street and onto the field.
The existing storm water pipes are undersized, severely corroded, plugged with sediment and likely have portions that are collapsed. The covered ditch has almost completely collapsed. Flood waters draining into inlets in the center of Main Street are deteriorating the road. The diminished functionality of the system has resulted in frequent flooding across Main Street and associated impacts to area businesses and residents. Water collects in the middle of the street which results in ice and water build-up around the drains and leads to water and ice flowing onto the parking area, sidewalks and businesses that front onto
Main Street. Businesses fronting the north side of the street have been particularly impacted, including City Hall, the Post Office, and the local grocery store who have all experienced water flows under their front doors. Water flows, which in cold weather lead to ice, is a concern for the public accessing the impacted businesses, as well as damage to doors, door jams, and sidewalks from the freeze-thaw process.
In addition, the unmanaged storm water results in sheet-flowing of water carrying debris including sediment, oil, chemicals, pesticides and other debris from the impervious surfaces in the Town. Unmanaged storm water impacts the area watershed, including Big Sandy Creek which is a tributary to the Milk River. These non-point source pollutants negatively impact area habitat and water quality.
There are three alternatives to be considered. Problems with the storm water system have been identified in the previous section. The alternatives presented to address the problems with the existing storm water system are included below.
• Alternative 1: No Action
• Alternative 2: Install new trunk line down Main Street and concrete median with inlets
• Alternative 3: Crown main street and provide new trunk line and inlets at intersections
Alternative 1: No Action
This alternative would involve continued use of the existing facilities without any modifications. No action will result in continued flooding on Main Street and associated impacts to businesses and residents.
Alternative 2: Install new trunk line down Main Street and concrete median with inlets
This alternative would consist of installing approximately 550 and 270 feet of new 18-inch diameter RCP storm drain trunk mains along 1st and 2nd street, respectively. These two trunk lines would replace existing pipe and discharge into existing ditches. In addition, approximately 662 feet of new trunk main would be installed along Main Street between U.S. 87 and 4th street. Main Street's cross section would remain an inverted crown and continue to slope to the center of the street. A 6-foot-wide concrete median barrier with curb and gutter and additional inlets and laterals to the new trunk main would be installed to facilitate drainage. Drop inlets would be installed along the median curb and gutter at the intersection of 1st and Main, halfway between 1st and 2nd street, and at the intersections of 2nd and Main and 3rd and Main. All existing inlets would be replaced and include sediment catch basins. The cost of this alternative is $454,221
Alternative 3: Crown main street and provide new trunk line and inlets at intersections
This alternative would consist of installing approximately 550 and 270 feet of new 18-inch diameter RCP storm drain trunk mains along 1st and 2nd street, respectively. These two trunk lines would replace existing pipe and discharge into existing ditches. In addition, approximately 655 feet of Main Street would be regraded with a crown cross-section and curb and gutter, from U.S. 87 to 2nd Street. Curb and gutter would convey storm water along the sides of Main Street to drop inlets with sediment catch basins located at the intersections of 1st and Main and 2nd and Main. Approximately
435 feet of new trunk main would be installed along Main Street, mostly between 2nd and 3rd Street. All existing inlets would be replaced and include sediment catch basins.
The total cost of this alternative is $710,017
Alternative #2 recommended by KLJ Engineering.
Before the project can be implemented, the funding must be in place. The estimated total funds required to complete the selected alternative is $454,221 and is presented in Table 5. The funding strategy includes a TSEP, RRGL, CDBG and the Town's general fund money. The funding strategy has been summarized in Table 10. The Town will apply for a $125,000 RRGL grant, a $100,000 CDBG grant, providing $25,000 in local funds from the Town's general fund, and a $204,221 TSEP matching grant. To determine the Town's eligibility for TSEP funding a target rate analysis was completed. The Town's target rates are included in Table 4. The water only target rate is $46.04/EDU/month, the sewer only target rate is $29.60/EDU/month; therefore, the sewer and water combined target rate is $75.64/EDU/Month. The Town currently exceeds the target rates, with a combined water and sewer rate of $105.90 per home per month. If the Town requires a loan to provide the $25,000 in local funds, the sewer rate is estimated to increase by about $1.65/EDU/month (2.5% APR 5-year term). The town will be responsible for the $1,000 audit fee.
The residence of Big Sandy as an opportunity to learn more and give their input again on April 2nd.