A guide for flood prevention

City council discusses flood mitigation with ISG

By Per Peterson

Will flood basins be carved out in the middle of Tracy someday?

It’s an idea that’s part of a flood mitigation proposal presented by ISG to the Tracy City Council on Monday during a Stormwater Management Study that included two flood prevention options — one for an estimated $639,845, the other for $960,595.

The purpose of the study comes on the heels of recent flood events, including the most memorable one in 2018 when seemingly half the city was under water. The goal is to develop a plan to mitigate future flooding issues and concerns.

ISG, an architecture firm the City has been partners with for years with the ongoing road infrastructure project, developed a hydrologic/hydraulic model for the City as a whole and its drainage networks. The model was used to analyze the existing system’s performance and identify flood-prone areas in town.

“What we have right now is a system that mitigates really well against a 10-year flood event; what this would do is solve the 100-year flood event — that 2018 flood,” Tracy City Administrator Erik Hansen said Monday. “It’s a question of degrees. Where we’re at today is better than we were a few years ago. If we were to do these kinds of improvements it would guard us against that worst event, that 2018 event. Ultimately, this is a guide for us. It doesn’t mean that this is what is going to happen, but it allows us to have some of that initial engineering work to be done.”

The council was presented numerous aerial maps of the city Monday, outlining areas of concern and possible sites for flood mitigation within city limits. Those include possible basins at Harvey and 4th streets and at Central Park.

“Our intention with this study is to evaluate how well-prepared the City is for large storm events and whether the city is meeting the expected level of service,” Andrea McEachran, an engineer for ISG’s Water Resources Group, told the council Monday. “We look at what projects can be done to mitigate flooding during a 100-year storm, which has a 1% chance of occurring in any given year — in Tracy, it’s about 6.7 inches in 24 hours.”

McEachran said Tracy is split into three separate drainage areas: the West Drainage Area (132 acres) which drains into a stream to the northwest of the city; the East Drainage Area (335 acres) that drains into a stream to the northeast of the city; and the South Drainage Area (544 acres), which drains into JD 23.

“Each of these drainage areas has its own model,” McEachran said. “The model we used is really an advanced tool that can be used to simulate some of the flooding events and see what the ponding will look like during flood events.”

McEachran said the City’s current draining system would perform well during a 10-year flood event (about 4 inches in 24 hours).

See this week’s Headlight Herald for more on this article.