Environment – Classroom Presentations
CLEAN CURRENTS 2026
Time: 11:15 AM - 12:15 PM
Day: 9/24/2026
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Details about each presentation and the speakers are below:
In this session:
Adaptive Sediment Management at Cowlitz Falls Hydroelectric Project: From Concepts to Implementation
Evaluating Through-Turbine Passage as an Economic Compliance Solution – New England Case Study
Saving an Island to Provide Environmental Flows for Fish Habitat – A TVA Success Story
Adaptive Sediment Management at Cowlitz Falls Hydroelectric Project: From Concepts to Implementation (Northwest Hydraulic Consultants / Lewis County PUD)
Presented by Ed Fordham, Northwest Hydraulic Consultants
Our story centers on technical implementation of sediment monitoring, application of sediment budgeting, navigating compliance between producers and regulators, educating regulatory partners, and shaping a path forward through adaptive sediment management. The Cowlitz Falls Hydroelectric Project (the Project), located in southwest WA State, operates in a run-of-the-river mode and is equipped with low level sluice gates for transporting the naturally high sediment load delivered from the upstream glacial and volcanic terrain.
In 2018, WA state regulators set strict water quality guidelines on the Project, which were intended to prevent sediment discharges that can occur during drawdowns. These guidelines are enforced as turbidity thresholds that require continuous data collection and monitoring. Since 2018, the Lewis County Public Utility District (District) and Northwest Hydraulic Consultants (NHC) have been working together to build a state-of-the-art sediment monitoring network at the Project.
Through a progression of required reporting and analysis, NHC has leveraged the sediment monitoring data to introduce the District and the Regulator to a sediment budget framework which quantifies sediment inputs, outputs, and changes in storage. Combined, the monitoring data, high resolution bathymetric scans of the forebay, and the sediment budget reveal that the annual cost of turbidity compliance is the accumulation of approximately 100,000 yd3 of sediment, about half of the incoming load from the upstream basin including inputs from Mount Rainier, Adams, and St. Helens. If left unchecked, 1,000,000 yd3 will accumulate over the next decade.
This sediment surplus looms in the reservoir, where it is likely to be released in mass during the next low flow maintenance drawdown when riverine conditions become necessary for both scheduled and unforeseen emergency maintenance. To meet the needs of the District and regulatory requirements, NHC proposes a pre-maintenance drawdown sediment flushing regime to actively flush sediment in a controlled manner from the headpond prior to known upcoming maintenance. Pre-maintenance flushing will certainly lead to low magnitude, short term turbidity exceedances, but it is a reasonable alternative to uncontrolled sediment discharges.
The sediment monitoring network captures key sediment fluxes throughout the basin and the sediment budget framework contextualizes sediment dynamics in terms that are relatable to technical experts, regulators, and producers. However, questions remain regarding the proposed operational changes. Rather than embarking on a modeling journey, implementation of the recommended sediment flushing will kick off a period of active study, where flushing operations at the dam will yield monitoring results that will inform next steps.
Evaluating Through-Turbine Passage as an Economic Compliance Solution – New England Case Study (Natel Energy)
Presented by Abe Schneider, Natel Energy
For owners of aging hydroelectric facilities, the staggering capital costs associated with new environmental compliance mandates often pose a direct threat to long-term project viability. When facing strict regulatory requirements for downstream fish passage, dam owners are typically forced into evaluating traditional, maintenance-heavy exclusion screens that introduce massive CAPEX and OPEX burdens.
This presentation details a recent comprehensive feasibility study conducted at a multi-megawatt hydroelectric facility in New England. Partnering with the facility's asset owner and lead engineering consultants, the project team set out to objectively evaluate multiple alternatives to address downstream passage requirements for sensitive species. Initial assessments of traditional exclusion methods, including full-depth screens and floating surface booms, revealed prohibitively high capital costs and significant operational drawbacks that threatened the site's economics.
Faced with these hurdles, the team evaluated a completely different approach: replacing the facility's existing Kaplan runners with advanced runner designs that enable safe through-turbine passage. This session details how computational fluid dynamics (CFD) and specialized biological modeling were utilized to objectively assess the through-turbine alternative against traditional screening methods.
Attendees will learn how the study modeled the potential for modern runner replacement to achieve high survival rates for targeted species and yield a notable increase in average annual energy production, all while avoiding the massive capital costs of traditional screening. Ultimately, this case study offers a concrete, highly transferable decision-making framework for operators evaluating the complex trade-offs between regulatory compliance, capital expenditure, and plant performance.
Saving an Island to Provide Environmental Flows for Fish Habitat – A TVA Success Story (Mesa Associates / TVA)
Presented by Boualem Hadjerioua, Mesa Associates, Inc.
Hibbs Island, nearly 10.6 acres in size, is located on the Clinch River in Norris, TN about 1 mile downstream from Norris Dam, owned by the Tennessee Valley Authority. Norris Dam impounds water for a 110-MW hydroelectric powerhouse and creates varied flows that have negatively affected the stability of the reregulating weirs on either side of Hibbs Island. These reregulating weirs, connected by the island, act as a small dam that was built to maintain a sustainable downstream flow from Norris Dam.
The reregulating weir maintains this flow during off-generation periods through a series of controlled and uncontrolled low-level pipes that ensure a constant minimum flow downstream. This minimum flow is paramount for the local fishing attraction.
High flow releases from Norris Dam caused part of Hibbs Island to erode and deteriorate. If no action is taken, Hibbs Island could eventually disappear, and the functionality of the weir would be eliminated due to the flow passing through the gap caused by the deterioration of the island. This would present the risk of tailwater flows becoming irregular and unable to sustain the aquatic life downstream of Norris Dam.
After performing an evaluation of Hibbs Island and conducting a hydrodynamic study of the high flows' impact on the Norris Dam tailwaters, Mesa Associates, Inc. came up with a solution to prevent further deterioration and instability of the weir. To guarantee long-term functionality of the weir, Mesa recommended placing a berm across the center of the island between the existing concrete weir abutments. The berm was built at an elevation to sustain high river flows and to ensure even the highest flows from Norris Dam are directed over the weirs instead of flowing over the island.
TVA used innovative methods to construct the Hibbs Island berm beginning in April of 2023, finishing in May 2024. TVA used a crawler carrier rubber-tracked vehicle to transport all the soil and rocks used for the berm from the shore to the island. This method of transporting the construction materials avoided barges or other invasive means of transportation that could have been more disturbing to the environment or cost-prohibitive for the project. Low-impact construction techniques for sites similar to Hibbs Island can be replicated by other utilities with similar concerns.
Since the installation of the berm across the island, all flows have been directed over the weirs, successfully maintaining their designed intent. The elimination of the water flow over the island has successfully eliminated island erosion and secured the reregulating weir operational objectives. Preserving Hibbs Island has been an effective solution for saving the existing reregulating weir and guarantees environmental flow for several miles of riverine aquatic life.
