Missouri River Reservoirs – Drawdown Protocols

GEI assisted PPL Montana with the development of special reservoir drawdown protocols.

The Problem

Drawdowns for emergency maintenance of hydropower facilities led to a FERC license requirement for PPL to develop special reservoir drawdown protocols. The reason for these protocols stems from the potential to disturb sediment and create water quality impacts on the Missouri River when pools are lowered. The potential for violation of water quality standards is present because of metals deposited in the sediment by historic mining operations.

GEI first reviewed existing water quality data and studies at five separate dams near the Great Falls region in Montana. Historically, sediment “events” were rare and appeared to be triggered by unusual hydraulic conditions.

The Solution

GEI designed an automated water quality sampling system and an interim reservoir drawdown protocol to minimize sediment mobilization. Through remote sensing, the GEI system monitors turbidity and triggers automatic sampling and emergency email notification of plant personnel. GEI designed the system, installed turbidimeters, automatic samplers, temperature probes, and other instrumentation at all five dam sites and incorporated them into the interface between the utility’s PC, the plant PLC, and the corporate computer network. We also developed applications to manage the data collected by these instruments for data analysis, reporting, and archiving. The program provides multiple preset interval status checks, and performs self and system diagnostics.

Unique Reservoir Drawdown Protocol

GEI developed a unique drawdown protocol based on bathymetry of the reservoirs and the potential of each site to mobilize sediments during drawdown. Sediment “spikes” occur at very specific reservoir elevations, as sediments are more or less exposed. By predicting where and when mobilization will occur, drawdowns limits or rates or pool elevations can minimize or protract these events to lessen their severity. Data will be collected during actual drawdowns to verify model predictions.