A 33” sanitary interceptor pipe lay exposed in the middle of the Un- named tributary to the Saline Branch (Photo 1). Rising water from a storm carries a large log towards the exposed pipe. The log rams into the pipe; the pipe bends but does not break—yet. Had the pipe broken, thousands of gallons per minute of raw sewage would have spilled into the Tributary; thousands of gallons per minute of stream and storm water would have entered the pipe, flooding the wastewater treatment plant and causing immediate sewage back-ups at the homes connected to the pipe. This scenario is occurring all over the United States as aging pipe in- frastructure crosses streams that were once small ditches, but are now large, flashy, urban streams. The pipe infrastructure is deteriorating due to having been installed 50 to 100 years ago, while the streams they cross have increased in size and strength. The combination of these two factors can be a hazard to public health and to the environment. In 2017, the American Society of Civil Engineers (ASCE) gave a re- port card on the United States infrastructure. We, as a country, received a D for Drinking Water Infrastructure and a D+ for Wastewater Infra- structure, which means the infrastructure is in poor to fair condition and approaching the end of its service life. Condition and capacity are of serious concern with strong risk of failure. So, the pipes carrying our drinking water and wastewater have a strong risk of failing and many of those pipes cross streams. Years ago, when most of the drinking water and wastewater pipes were installed, pipes crossed small ditches. However, as more areas were developed and more rainfall ran off into the ditches, they grew into large streams with serious erosive capabilities. Broken pipes often cause adverse environmental impacts, in addition to harming and inconveniencing the community. Boil orders and sew- age backups into basements can cause damage and frustrate homeown- ers. Emergency fixes to the pipe, the stream, and the water/wastewater plant can be expensive while also leaving the public with a negative impression. Performing stream restorations at pipe crossings protects aging infra- structure and also provides communities with urban green space and has numerous ecological benefits. A stream restoration is the manipula- tion of the physical, chemical, and biological characteristics of a site with the goal of returning natural/historic functions to a former or de- graded aquatic resource. Stream restorations stabilize streambeds and Protecting Infrastructure Through Stream Restorations By Emily Poynter Jenkins
A 33-inch sanitary interceptor pipe exposed in the middle of the Unnamed Tributary to the Saline Branch. Photo: Jenkins / Farnsworth Group
banks to prevent scouring of pipes and improve the basic functions and ecology of stream systems. In addition, people are drawn to natural spaces, particularly when they are easily accessible in urban areas. Restoring sections of stream in urban settings can provide personal wellness opportunities to the com- munity. What once was a liability can become an asset for the com- munity and the environment. Protect Infrastructure Water is powerful. Water can cut into banks, undercut pipes, and erode pipe and bridge footings. I have seen a 33” sanitary interceptor that was once buried under a stream, completely exposed with the stream flowing under it. Another stream cut into its bank until a large exposed vertical streambank was 20 feet away from a home. A stream restoration not only redirects the flow of water away from the bank but also from infrastructure. We can direct the flow of water into the center of the stream using large boulders, logs, or tree root wads placed in the streambed. The boulders or logs are placed to create structures that force water to slow down near the bank, then speed up as it cascades over the boulder into a center pool in the middle of the stream. We can also spread the water out onto the floodplain to slow down the water and decrease the force it has on the streambanks. When stream- flow is confined to a narrow, deep channel, the flow increases and the water can erode banks and infrastructure easily. When the streamflow can spread out over a floodplain, the flow is slower and banks are more protected. In Champaign, Illinois, an electrical box was located on the outside bend of the Copper Slough. The stream had eroded the bank away, leaving the electrical box only a few feet away from a vertical, unstable streambank. Farnsworth Group, a full-service architectural and engi- neering firm, protected the electrical box by restoring the stream. Boul- der structures were used to direct water into the center of the stream, away from the bank with the electrical box. A small ledge, or bench, was graded into the bank to allow water to spread out and slow down during rain events. The bend in the stream channel was adjusted to be
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csengineermag.com march 2020
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