On this spooky Friday, the 13th, let’s travel to Northern Georgia, to the Army Corps’ manmade 38,000-acre reservoir, Lake Lanier. Designed for flood control, water supply, and to provide hydroelectric power, Lake Lanier was made by building the 1,630-foot-long Buford Dam on the Chattahoochee River. Construction began in the mid-1950s and by the time it was complete, areas of farmland, residences, and entire towns were covered by the ‘flood.’ These areas were abandoned of course, but not without using eminent domain to buy the land.
The reservoir is a major water supply source (states are even fighting over it), provides a significant amount of hydroelectric power to the Atlanta region, and is used to prevent downstream flooding during heavy rain events. But it has also become a popular recreational spot for boating, fishing, swimming, camping, you name it.
This big engineering feat was done nearly 70 years ago before they could use AutoCAD to perfectly scale and dimension site features or get accurate GPS coordinates and elevations by flying a DJI Matrice 300 Drone.
Now onto the spooky stuff. I mentioned they flooded entire towns to make this lake. This included cemeteries that had some unclaimed, unmarked graves that may or may not have been left behind. Many visitors claimed to have felt arms or legs when reaching into the murky water and others have even felt something pull them down. Over 500 people have died at the lake since its inception, including the ‘Lady of the Lake’ who was driving with a friend when she lost control of her car and disappeared over a bridge. Many people have claimed to see her wandering along the bridge at night like she was lost. It took 32 years before her car was discovered with her bones inside.
Despite its haunted history, well over 10 million people visit it each year—some for its beautiful scenery, others for the ghostly sightings. Next time you’re down south enjoying fresh water from the tap and not being flooded out, thank the engineers who made it happen… and the Lady of the Lake who may be there in spirit.
4RC – “The sight distance triangle shall be shown” for a new driveway… at the end of a cul-de-sac.
With the weather warming up and homeowners working on spring cleaning and yard maintenance, don’t forget about those stormwater BMPs! Most improvements involving the addition of impervious surfaces require stormwater management. For small residential jobs such as house additions, patios, or swimming pools, this usually means a subsurface stone seepage bed. Larger projects may utilize rain gardens or detention basins.
Municipalities will often require homeowners to sign into an agreement to maintain the required stormwater management features. These agreements include regular inspections of these features. No two agreements are the same, but they typically require the following.
Starting with what you can see from the surface, the grading and drainage patterns will be examined to ensure stormwater runoff drains to the appropriate inlets/yard drains with no erosion or ponding. Roof drains need to be checked for clogging so that they drain adequality, whether it’s to a splash block or directly to a subsurface bed. Inlets and yard drains should be inspected for debris and sediment accumulation. For above-ground basins and rain gardens, the bottom, side slopes, and piping are inspected for erosion and adequate vegetation. If there are any trees near the stormwater BMPs, it is important to make sure there is no intrusion from root growth.
Seepage beds are designed with cleanouts and/or maintenance ports to access the subsurface features of the bed and perform visual inspections. We review water and sediment levels through these maintenance ports. Ideally, the bed will be empty. But if there is standing water and the most recent rainfall was more than 72 hours prior to the inspection, then infiltration problems exist, and further investigation is needed. If the stormwater system has an outlet structure, then it will be reviewed for sediment or water accumulation and to confirm the individual pieces (weir, orifice, or other flow control feature) are intact and undamaged.
The requirements for operation, maintenance, and inspections depend on the type of system and the agreements with the municipality. I always say this, but every township is a little different. If you have a stormwater management system on your property that needs inspection but aren’t exactly sure what is required, don’t hesitate to reach out to DLHowell so we can take care of it!
We all know the seriousness of ensuring your site is designed with accessibility in mind. Not just to comply with applicable codes but also to make sure your site is accessible to all potential users, whether it is a 500-unit apartment complex, a retail shopping center, or a mom-and-pop restaurant. Although the International Building Code and International Residential Code mostly cover features internal to the building, we civil engineers need to know a few things from these codes for exterior features. One of these being handrails.
When do you need handrails?
If your project falls under the IRC, exterior steps need handrails if you are proposing 4 or more risers, and each riser cannot be higher than 7¾”. If your project falls under the IBC, it is a little more complicated… there is a whole section in the IBC dedicated to handrails. Whether or not you need handrails depends on if you are looking at a ramp or risers. For ramps (which could be a whole separate blog post!), handrails are needed if there is a rise greater than 6” across the ramp. Risers throughout a site, whether it is a long stretch of steps or a few steps here and there, almost always require handrails with few exceptions. The main exception being if you only have one step and proper landing depths, a handrail is not required.
It is important that civil engineers use this information when designing and laying out a site. We review all necessary codes and design our sites to meet all accessibility requirements while doing our best to avoid the need for excess steps, ramps, handrails, etc. Keep in mind that every project, every site, every municipality is different, and this is just a guide based on the currently available International Building Code (IBC, last updated January 2020) and International Residential Code (IRC, last updated September 2019), which are continually changing! Although this is a good summary of when handrails are needed, you still need to take into account local code requirements, which D.L. Howell is always happy to help you with!
Last week, two dams failed in Michigan, the Edenville Dam and Sandford Dam located on the Tittabawassee River. The Edenville Dam, built in 1924, was the first to go causing the failure of the downstream Sandford Dam. According to data from NOAA, the rainfall that caused these failures was between 7-8 inches over 36 hours. Based on NOAA’s precipitation frequency estimates for this area, this was greater than a 100-year storm. But on top of the 100-year storm, the failure of these dams caused catastrophic flooding with more than 10,000 residents being forced to evacuate (thankfully there were no casualties). I have seen estimates say some areas of Midland, MI could be under 9 feet of water, and at one point the Edenville Dam was discharging up to 374,000 gallons per second. That is a LOT of water.
When we design stormwater management systems on our sites, we are required to design them up to the 100-year storm. But what is the 100-year storm and are they as catastrophic as this one is? Some think it is simply a storm that happens every 100 years, but weather is not that predictable. It is a storm that has a 1% chance of happening in any given year. A storm like this could happen 2 years in a row, though unlikely. When it does happen, the downstream impact depends on many factors including soil infiltration capabilities in the areas, how wet the soils are immediately before the storm, how many stormwater management facilities are in place, how much impervious cover and other improvements are in the rainfall area etc… Answering this question is not simple, but that’s where the fun comes in! When engineering stormwater systems we look at all these factors and more to optimize our systems. Stormwater management on your new development site might be a costly pain, but at the end of the day they help curb negative impacts of heavy rains.
Back in the middle of the summer we took over a job that was in the middle of the review process. iRoy Sport and Fitness is a gym located in East Norriton Township owned by Yori Adegunwa. Taking over a job from another engineer is always a challenge, and on top of that, the new site for iRoy has provided us with some interesting engineering challenges.
The proposed gym will be located along Germantown Pike in Lower Providence Township. Existing conditions at the proposed site include a rundown bridal shop, a few deteriorating buildings, a ton of overgrown vegetation, and some dying trees. It’s quite an eye sore.
The new location is a little over 4 acres and has a grade change of about 32 feet across the site. Finished floor elevations, retaining wall heights, stormwater drainage patterns, and driveway slopes, are all factors that we need to consider during the design phase to balance cuts and fills. Two retaining walls and a steep hill in the front of the building had to be incorporated into the design to make the layout work.
Shallow weathered rock and bedrock were encountered throughout the site during geotechnical investigations. Infiltration was almost nonexistent during testing. How are you supposed to satisfy Township and County Conservation District infiltration requirements if your soils won’t let you? Thanks to the newly released managed release concept (MRC) (https://www.dlhowell.com/blog/pa-dep-releases-guidance-for-managed-release-concept/) you can now achieve the requirement without actually infiltrating. This may seem like an easy fix, but you will most likely need a waiver from the Township to do this and need to do extensive infiltration testing to prove there are no other options.
For this project, we had to design an MRC system, which is more complicated than it might seem. Although there is no “infiltration volume,” there is a volume that needs to pass through water quality features and a volume that needs to pass through the small “slow-release” orifice. Discharge rates must be below a certain value, but you also need to make sure the system will fully dewater within a certain time period. It’s a balancing act to make sure the discharge rate is slow enough, but also fast enough.
Despite some struggling with the new MRC design and the large grade change across the site, the iRoy Sport and Fitness job has been an interesting project to work on. We here at DL Howell are always ready to take on a challenge!
Some of the D.L. Howell team recently visited a few Coatesville middle schools to present to students in the Chester County Futures’ (CCF) “Futures AHEAD” program. Futures AHEAD is CCF’s middle school program that provides assistance and enrichment to students coming from low-income homes. We had the opportunity to show the students a little about what we do. We presented to them about our careers in civil engineering in a way they could understand and tried to relate our work to topics they are learning in school now. The kids had the opportunity to see a drone, and one of our drone experts, Dave Gibbons, gave a brief presentation of how they work and what we use them for in our line of work. Unfortunately, we were too close to the Chester County G.O. Carlson Airport and the invisible fence prevented us from doing a flight demonstration, but the kids still enjoyed seeing a drone up close! After the presentations, we had a little friendly competition with the students. The goal was to build the tallest tower that could hold the weight of one marshmallow using only uncooked spaghetti, string, and tape. It’s surprisingly more complicated than you might think! We had a good time teaching the kids about engineering and building our spaghetti towers with them. But more importantly, the students learned about our careers and how what they are doing in school now can help them become an engineer.
Chester County Futures is a great program that provides support to low-income middle and high school students, helps prepare students for college, and offers scholarships for post-secondary school. The program was founded in 1996 and has since helped over 850 students. You can learn more about the organization at ccfutures.org.