Kent County is working with the community to adjust the way it estimates precipitation frequency in the area.
Civil engineer Angie Latvaitis said the Kent County Drain Commissioner’s office is collaborating with Grand Valley Metropolitan Council and Kent County municipalities to update their standards under the NPDES Ph2 MS4 permit, which is under review by the Michigan Department of Environmental Quality.
She said the rainfall frequency usage will be measured by Atlas 14, which has rainfall data between 1992 and 2012, according to Brad Boomstra, senior engineer for the Kent County Drain Commission.
“Atlas 14 incorporates an additional 20 years of rainfall data since Bulletin 71, which is our current rainfall standard (that) was published in 1992,” he said. “Prior to Bulletin 71, Technical Paper No. 40, or TP40 was used. TP40 was published in 1961. The additional years of data make the design rainfalls more accurate for stormwater design.”
Steve Teitsma, senior civil engineer for Progressive AE, an architectural design and engineering firm in Grand Rapids, said the industry is changing to adjust to climate change because the new system will consider the most recent severe and frequent storm events.
Although the heavy rainfall in 2013 and earlier this year that resulted in the Grand River cresting well above flood stage will not be included in Atlas 14, Teitsma said the new rainfall data will allow civil engineers to adjust the size of the drainage systems they use when constructing a building.
“When we design a site, we need to size the storm sewer, the pipes that carry the stormwater away or the detention basin or any of that infrastructure underground, and the way to size that is by using rainfall data to determine the amount of water that is going to impact that system,” he said.
While Teitsma waits on the county to update its standards, he said in an effort to mitigate the possible flooding experience for downstream property owners he tries to mimic natural hydrology — the movement of water — as much as possible.
“Some of those practices could mean putting in porous pavement so that the water actually runs through the pavement and into the ground, as opposed to running off the pavement and into the storm sewer,” he said.
The soil that is beneath the pavement is sand, so it can absorb the water. Teitsma said if the sand becomes too saturated, there is an underdrain system that removes the excess water from the property.
Atlas 14 will help architects update the barriers they use to protect water from entering a building. Bob Pomeroy, vice president and senior architect for Fishbeck, Thompson, Carr & Huber Inc., said to prevent water from flooding a building, his firm uses flashing, which is either a thin sheet of metal or a flexible membrane, so that if water gets behind a brick wall there will be a barrier to prevent the water from entering the building.
“The water will trickle down, still on the outside of the building, if you will,” he said. “It will get over to the side of the window or door opening so it is not working its way in and above the window and into the space. So, we try to get it out and around the side of the building until it continues its path to the bottom of the wall where there are openings at the bottom where the water migrates its way out.”
Pomeroy said flashing has been around for a long time, but the technology continues to improve.