Repair of Emergency Spillway of Mueller Pond
Client: Mr. Larry Mueller
Client Representative: Richard Russell, Ollis and Company
Location: Strafford, MO
Project: Repair of Emergency Spillway of Mueller Pond, AE 20108-15, 20079-15
Date: 2015 to 2017
Anderson Engineering Design Team: Steve Brady, P.E., Jared Davis, P.E., John Snider, P.E., Kevin Lambeth, PLS, Jeff Davis, Construction Testing and Inspection Leader
In summer of 2015, torrential, heavy rains caused the emergency spillway of the Mueller Pond to erode, putting the earthen dam at risk. The dam was holding back about 30 feet of water in a 10 acres pond. The fast moving water was able to erode a gully into the spillway, further accelerating the water in the spillway. Much of the spillway rock was washed to the bottom of the dam.
Anderson Engineering was called in to assess the situation and develop a plan to solve the problem. Initial plans provided options to replace the rock back into location and armor it with concrete to keep the rock in place.
Smaller rock spillway – before erosion in 2015, and 2016
The original plan from the 1970s had a grass spillway, but due to erosion from a large rainfall in 2008 it was later modified to be covered with rock. However, calculations showed the rock size was too small.
We proposed to put the rock back and use concrete to armor it and keep the rock in place.
In early 2016, before the initial repair could be made, an unusual and unfortunate heavy rain after the initial repair plan caused even more erosion to the damaged spillway. The water was so intense that it took almost half of the rock blanket off the spillway and washed it to the bottom of the dam. This exposed giant gully washers in the earth dam – about the size of a small car, exposing the shale under the dam.
2016, Heavy, deep scours through the bedrock. Size of a small car
2016, Heavy, deep scours through the fill. About 5 to 6 feet deep
2016, most of the rock was washed away to the bottom
Another heavy rain would surely have scoured the spillway and possibly caused a breach of the dam.
Anderson Engineering was called in again to assess the situation and develop a plan to solve the problem. The damage was so intense this time that a more robust plan was needed. Detailed repairs plans were made of each gully scour. For the blanket we looked several options: concrete grouting, concrete, ArmorFlex mats, and rock boulders.
Due to the great amount of damage present, Greene County stormwater experts were called in to be made aware of the repairs to be done.
To expedite the repairs and develop alternatives, Mr. Mueller had selected a contractor, and we walked the site with him, Mr. Mueller and his team, and the Anderson Engineering design team. This allowed for very site specific repairs and some creative solutions.
With a local quarry nearby, we were able to get larger rocks to use as the surface blanket. But for the scoured areas and as bedding for the larger rocks, we used the “washed out rock” from the spillway. This created a big cost savings.
Also Mr. Mueller had a number of concrete blocks on hand from a local concrete company – creatively we were able to use them to armor the sides.
2016, Detailed Anderson Engineering Plans.
More key was being able to use the concrete blocks at the top of the spillway to “turn” the water so that it went straight down the spillway – instead of “riding the side” which concentrated water and scoured deeply in the hill side. These concrete blocks were money savers too, since we didn’t have to do poured in place, reinforced concrete. Also speed of construction was expedited since the contractor had all the equipment on hand to do the repair. We modified our plans to work with the contractor and Mr. Mueller’s team to best handle the situation.
During construction, we were able to provide inspections that adjusted and re-affirmed work needed to provide a safe and durable spillway.
The proof of concept came two years later in April 30, 2017 when large, intense rains re-appeared and caused a massive amount of water to go over the spillway. The ingenious repair concept worked.
2017, “turned” water, flowing fast and furious down the spillway. Right sized boulders protecting the dam, with concrete block along the sides for even heavier rains.
The concrete blocks turned the water nicely so that spillway water flowed down the blanket smoothly and uniformly. The force was tremendous but the rock boulders stayed put. 2016, Detailed, site specific plans, using creative ideas
2017, concrete blocks used to “turn” the water, preventing large, erosion and scouring along the sides
Mr. Mueller and his team were delighted with the results and re-assurance that this design worked as advertised. This is another success with the help of Anderson Engineering.
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