When runoff carries sediment into lakes and reservoirs, it can build up and eventually dramatically reduce water capacity. That poses a threat to important sources of drinking water, recreation, wildlife habitat, and even flood control. Hydro Leader talked to Jaclyn Gnusti, the senior managing engineer at Anchor QEA, about how her company tackles the tough problems caused by sedimentation through a variety of services that include aid with geotechnical and environmental evaluations, planning and permitting, engineering solutions, funding, construction implementation, and long-term maintenance.
Hydro Leader: Please tell us about your background and how you came to be in your current position.
Jaclyn Gnusti: I wanted to be an engineer starting as a kid, and I knew that I wanted to get involved in water issues because my dad was a farmer. We dealt with everything from droughts and water rights to saltwater intrusion. When I started working, I unintentionally became involved with dredging. Now, a couple of decades of experience later, in my current position as the senior managing engineer with Anchor QEA, I am able to combine the environmental and water aspects of many projects with my dredging experience to help project owners, including some from the agricultural community, resolve water and sediment problems. We help create more capacity for irrigation water and even provide dredged sediment as a beneficial resource for agricultural lands.
Hydro Leader: Please tell us about Anchor QEA.
Jaclyn Gnusti: Anchor QEA is an environmental science and engineering consulting firm that has been around for over 20 years and has clients across the United States. We work with our clients to plan, design, and manage near-shore and aquatic-based projects from the initial planning, site investigation, and feasibility evaluation stages through design, plans and specifications, construction management, permit compliance, and environmental monitoring.
Hydro Leader: What causes sedimentation in lakes and reservoirs, and why is it a problem for water managers?
Jaclyn Gnusti: In reservoirs or lakes, sediment accumulates over time, creating a multitude of problems. Sediment can reduce the capacity of a water body, affecting its ability to serve its flood control or irrigation and emergency water supply uses. It also creates water quality issues: The reduction in depth or the introduction of nutrients or contaminants affect the water quality and can cause nuisance vegetation, such as toxic algae, to grow. The toxins can then interfere with municipal, irrigation, or household uses or affect recreational opportunities, for example by causing swimming and fishing to be temporarily banned.
Something we’re seeing a lot more of, especially with aging infrastructure, is that sedimentation can affect existing dams. Many of these dams weren’t built with sediment loads from upstream developments or even natural erosion in mind, and they weren’t built with a mechanism to remove the sediment. As sediment builds up on one side of the dam, it can create instability. Removing sediment may also create unanticipated structural problems, because the dam may have started to rely on the sediment for structural stability as it settles over time. And if a dam wasn’t designed with management in mind, there is often little space to get dredging or other equipment in to remove the sediment. We’re seeing issues like that all over the country. As problems with sedimentation near dams grows, the need for creative solutions also grows.
Hydro Leader: Why is this issue worsening? Are things like climatic changes and wildfires factors?
Jaclyn Gnusti: I think a combination of factors is leading to sedimentation and water quality issues. Runoff from wildfires or urbanization can introduce contaminants into a lake, where they accumulate and eventually affect water quality. There is also a lot of new science out there, so we’re paying more attention to potentially toxic or nutrient-laden sediment, how it affects the environment, and how we need to clean it up. Finding funding to address these issues is always a problem, though. These are no easy solutions. and there’s no one-size-fits-all approach.
Hydro Leader: Where does Anchor QEA come into this? If a dam owner or operator has a sedimentation issue, how do you address it?
Jaclyn Gnusti: We can fit into any part of the project identification or solution. Our hydraulic engineers can determine the sediment load, we have a geotechnical department for dam and slope stability, and we have scientists who perform sediment characterization. Our civil engineers design plans for sediment removal, and we have a dedicated group for construction management. Another specialized area of ours is environmental planning, which helps clients comply with the National Environmental Policy Act (NEPA), the California Environmental Quality Act (CEQA), and other state or regional environmental regulations. Throughout the country, we’re able to prepare the necessary localized regulatory documentation and coordinate the acquisition of permits. I think the biggest thing that owners underestimate when they have a sediment management project is probably the time the regulatory process requires and the steps involved.
One of our principal Anchor QEA engineers, Michael Whelan, has made numerous technical presentations on sediment management in lakes and reservoirs to groups such as the Western Dredging Association and Denver Water. In each of his presentations, he hits on all the important topics we can help with—the identification of the problem and its sources, geotechnical and environmental evaluations, planning and permitting, engineering solutions, funding, construction implementation, and long-term maintenance.
Hydro Leader: Does construction management mean that Anchor QEA works alongside a construction company and directs what it does?
Jaclyn Gnusti: No; in this role, instead of directing contractors, we usually want to refer them back to the plans and specs, which in some cases we’ve developed ourselves. We make sure that the contractors comply with all regulatory requirements. If they run into a problem, we could help them come up with a solution that complies with those requirements, but all means and methods are the contractors’. We can do everything from full construction management—in which we are on site on a daily basis to act as the owner’s representative—to limited support, which means we only oversee the regulatory submittals and review the progress reports and the pay requests from the contractor. There is an array of services we can provide, depending on the type of project and the type of client.
Hydro Leader: Would you give us an example of a sedimentation project you’ve worked on?
Jaclyn Gnusti: We were called in to address sedimentation issues at Temescal Lake, a 13‑acre artificial lake in northern Oakland that was constructed in the late 1800s. It is owned and managed by the East Bay Regional Park District and used for recreation with some capacity for flood control. When it was built, the lake had depths of 60–80 feet, but now it is less than 15 feet deep. That’s because of the rapid urbanization of Oakland, Berkeley, and the surrounding areas. Not only is the lake filling in, but the sediment is pulling in all the toxins from development runoff, and it has blooms of cyanobacteria, or blue-green algae. Because of that, the district has had to shut the lake to pets and restrict fishing.
We were brought in to do a feasibility study, to identify the problem, and to propose some solutions. We came up with a twofold solution. First, we recommended a mass sediment removal project for the immediate restoration of the water body. Second, because that is only going to work for so long before the problem returns, we also presented some proposals for long-term maintenance.
We initially collected some exploratory sediment cores and performed lab testing to determine the chemical makeup of the sediment. Then, we performed a geotechnical assessment of the existing dam. With this information, we came up with three solutions for restoring the lake: dredging, installing treated wetlands, and creating sediment catchment basins. The dredging solution included restoring the water depth to about 30–35 feet by removing about 180,000 cubic yards of sediment. The purpose of the treated wetlands solution would be to remove the nutrients from effluent or runoff before they run into the lake. Finally, the purpose of expanding some of the existing sediment basins, or forebays, would be to intercept the sediment before it enters the lake. It’s a lot more cost effective to remove the sediment from those basins, because land-based equipment can be used rather than dredges in the lake itself. The dredging solution was complex: We looked at different dredging options, such as hydraulic or mechanical dredges, and at geotextile tubes to dewater the sediment once it was removed. We also looked at possible areas in which to process and store the sediment. Could we leave it on site and modify some of the park features, or would we have to truck it to another location? Using a landfill is usually the last resort because of the cost, but we considered that option, too. We wrote a feasibility study, and now the district has enough information to move forward—first, to obtain funding, and second, to plan the next steps, which would be permitting and environmental investigations.
Another project we worked on was construction management for a sediment excavation operation at Phoenix Lake, an 80‑acre water storage reservoir in Sonora, California. We came in to oversee the contractor’s compliance with permitting regulations and design. Managed by the Tuolumne Utilities District (TUD), Phoenix Lake is a primary drinking source for over 10,000 residents. It’s also the primary fill source for California Department of Forestry and Fire Protection helicopter operators and provides habitat for migratory birds and aquatic wildlife.
The CEQA document determination was that draining the lake was the best option for sediment removal. That would allow workers to use land equipment, such as excavators and dozers, instead of using traditional dredging equipment. Even though it was a dry summer and the contractor had installed over 80 ground pumps to keep the water at bay, the contractor couldn’t access about one-fifth of the project area because it was too wet. In this project, TUD was able to collaborate with an adjacent landowner and deposit the sediment in an orchard. That really cut down on transportation costs, because this much sediment might require over 10,000 truck trips. Additional tasks included overseeing habitat surveys and fish relocation during lake draining.
Hydro Leader: Would you tell us more about what makes permitting so challenging?
Jaclyn Gnusti: As I mentioned, the regulatory process can vary by location and water body. Nearly every project requires some type of environmental act approval. In California, we have CEQA, and there’s NEPA on a national level. For CEQA, you first need to have a local sponsor or agency. If the owner is a public entity, such as a county or city, it can be the responsible agency, but if it is a private entity, such as a homeowners association, it needs to engage a public entity. Typically, maintenance projects are exempt from CEQA, but any type of large-scale project falls under it, and can be anywhere on the scale from receiving a mitigated negative declaration, which is a declaration that there is no environmental impact, to requiring mitigation measures or an environmental impact report. Those impact reports are more in-depth and can take months or years to complete. They might require environmental studies, such as habitat surveys or sediment testing. For some projects, you also have to conduct cultural resource surveys covering potential effects on historical or archaeological resources. Then, there is a public commenting period during which members of the general public, public agencies, and adjacent landowners can provide input on the project. After that, there’s an array of permits to obtain, which can include both state and federal approvals. The U.S. Army Corps of Engineers, for example, has to approve work in certain wetlands or anything tied to federal waters. Sometimes, local agencies get involved, too. It really varies from state to state and from region to region.
As you can imagine, gathering all that information and getting approvals to move forward takes time. The smartest thing to do at the start of a project is to develop a flow chart of events so the planning team is on the same track and there are not a lot of surprises coming down the road.
Hydro Leader: You mentioned that older structures may not have been designed with a mechanism for removing sediment or even a sufficient pathway to do so. How does awareness of these issues affect how new structures might be designed today?
Jaclyn Gnusti: We make sure that any new reservoir or lake will be as easy to maintain as possible, so we include things like forebays, or basins, that can be easily and routinely cleared out in a manner that is much more cost effective than dredging. It is also important to make sure that there are lay-down areas or open space that can be used for equipment access or sediment processing, so we recommend not building out the entire perimeter of the lake.
Hydro Leader: Is there anything you would like to add?
Jaclyn Gnusti: I would emphasize that one of the most important things is to engage early with the regulatory agencies, because that really can direct the path of the project, its cost, and the different types of solutions that can be implemented.