UD Prof Leads Effort to Monitor Indian River Inlet

Article by Diane Kukich

Jack Puleo, Assistant Professor of Civil and Environmental Engineering, is leading a DelDOT-funded project to conduct scour monitoring of the Indian River Inlet in Sussex County, Delaware. Scour occurs when sediment, including sand and mud, is washed away from the bottom of a body of water. It can have serious effects on bridges when the bridge supports rest in or near scoured areas.
Construction on a new bridge over the Indian River Inlet is slated to begin in 2009; the new structure will be a cable-stayed bridge with all of its piers out of the water, eliminating the scour concerns of the existing span. In the meantime, DelDOT has installed monitoring equipment on the existing bridge, and the agency conducts regular safety checks of the span and its support structure.
The University team, including civil engineering graduate student Jesse Hayden, is interested not only in providing DelDOT with data about how rapidly the bottom is changing and whether the bridge is moving, but also in gaining a fundamental understanding of nearshore bathymetric processes.
"We know that over time, the depth of the inlet has changed," Puleo says. "Its typical depth is about 40 feet, but there are scour holes exceeding 100 feet. We're developing and installing tools now that will enable us to monitor the area continuously and in near-real time."
These include custom-made 3D acoustic profilers to locate the bottom of the inlet and acoustic Doppler current profilers to measure currents. Computers control data acquisition from the sensors, and, once the network connections are in place, the data will be available to the UD team on campus, almost 100 miles from the inlet.
Puleo explains that data collected by the Army Corps of Engineers every few years with high-resolution imaging equipment has shown the progression of scour holes. "But," he says, "it's not clear whether the changes occurred gradually or all at once, possibly as the result of storms. The equipment we're installing now will enable us to see what happens on short time scales."
One of the new tools that Puleo will be using in this effort is a personal watercraft equipped with a real-time kinematic GPS, a tilt sensor, an acoustic altimeter to determine depth, a monitor, and a keypad with "hot keys" to control data acquisition. All sensors are connected to an onboard computer and powered by a marine cell battery located on the craft stern.
Purchased with matching funds from the University of Delaware, the little vessel, which looks like a jet ski on steroids, is actually a low-cost rapid-response survey system for shallow water environments. "If we know a big storm is coming," Puleo says, "we can get in there quickly, take measurements, get out, and then come back in after the storm has passed to measure the effects."
"DelDOT wants to know as much as they can about the bridge and the bottom so that they can make informed decisions," Puleo says. "For us, the project is producing data that will enable us to explore such questions as 'Why did the scour holes develop where they did?' and 'Why are they growing the way they are?'"