Erin McConville ’21: Entrepreneurship Learning Competency

As a part of my senior design project, my team and I evaluated different design alternatives based on their cost to the City of Milwaukie and the return on investment to the city.

The City of Milwaukie tasked the University of Portland capstone team with a project to improve a transportation corridor along International Way between 37^th Avenue and Lake Road. International Way has experienced an increased amount of traffic due to the expansion of commercial and industrial businesses. For the city to improve the transportation corridor, they need to understand the current stormwater system with a computational model. With a better understanding of the system, the city leaders are interested in preliminary design plans to improve the stormwater network when improving the transportation corridor. The capstone team has been assigned these two deliverables for the City.

Currently, there are several open channels that connect the city’s stormwater infrastructure, including two culverts that cross underneath International Way. Now, the open channels and the culverts are filled with sediment, since they are not regularly maintained. This means that the flooding from year-to-year will likely worsen if the city does not take steps to prevent flooding. Any approach to fix the problem will cost the city a significant amount of money, but if the costs of sandbags and the cost to public safety are taken into consideration, it is a worthy investment for the city.

The project must have a reasonable budget for completion to improve International Way. An expensive, complex design, with large amounts of maintenance and fiscal and personnel resources make approving any project difficult. The city has allocated $174,000 in the 2021-2026 Capital Improvement Plan for addressing stormwater management around International Way. Besides the upfront costs of a project, there are maintenance and end-of-life costs such as residual value and demolition. A balanced design that has a reasonable upfront cost, practical maintenance, and a tolerable end-of-life cost is the economic goal of this project. Furthermore, the local economy and the effect this project has on it must be considered. International Way lies within a business park home to dozens of businesses of all sizes. Improving accessibility and safety on the roadway will sustain the growing, diverse economy of the business park.

To address the concern of stormwater flooding in Minthorn Creek, the source of the flooding, four preliminary design alternatives were assessed:

1. Upsize existing culverts (culvert resize)
2. Size up piping and install a new manhole to replace the bypass weir (manhole junction)
3. Install grassed swales along the roadway (swale improvement)
4. Install underground storage and infiltration (underground storage)

The culvert resizing design was selected to be the final design recommendation. It was selected due to its ability to address flooding issues, as well as its lower cost in comparison to the other three alternatives. The installation of a larger culverts will address the flooding in the immediate area surrounding International Way. This design allows for water to pass under the roadway, preventing flooding and ponding. In addition to this upsize, it is recommended that the surrounding channels be cleared of debris and sediment. In addition, resizing the culverts will not need any additional right-of-way to be purchased, therefore, it has the lowest construction cost of all alternatives (Table 1).

The cost of this project, $30,000, is much less than the allocated funds for the stormwater improvements, $174,000, within the larger budget of the International Way project. With this extra funding, it is recommended that the city start to dredge the existing open channels. An initial cleaning and replanting in the existing open channels will ensure that the time and money related to maintenance will be minimized. This also ensures that the city will not face larger flooding issues in the future, as the open channels become increasingly clogged with sediment.

Forecasted evaluations of the project area before and after the culverts were upsized showed that flooding decreased from 10% to less than 1% over a 10-year period. Based on this evaluation, the project costs associated with the upsized culverts are worth the initial investment.