Lake Level Management Plan

Purpose

This lake level management plan consists of the policies, intent, and procedures of the City of Lake Stevens for managing the water surface level of Lake Stevens.  The plan serves as a guiding document and is considered a living document subject to changes and revisions.  The plan reflects the expectations of City management and maintains flexibility for modifications.

Background

Lake Stevens is the largest and deepest lake in Snohomish County with a surface area of 1,040 acres, an average depth of 62 feet, and a maximum depth of 150 feet.  The Lake Stevens’ watershed area is approximately 3,500 acres. The lake has a single outfall that drains to the channel adjacent to Hartford Drive that discharges to Catherine Creek.  Lake Stevens provides benefits to aquatic life, stormwater management, and recreation.  

Lake Level Management

The lake level is managed by the City’s Public Works Department.  This is performed using a weir board system that is installed and maintained from April through October, depending on the weather.  The remainder of the year the weir boards are completely removed and the lake level is controlled naturally by the weather conditions and the capacity of the outfall channel.

Weir Structure

The weir provides a fish passage opening in the bottom board.  This allows for continuous flow for the outfall channel when the lake level is below the weir.  As the water level rises above the top of the weir, the overflow spills over into the outfall channel.  The weir is comprised of five wood boards that adjust the height of the crest.   These are placed manually and secured with a pin and locked. 

Monitoring

The lake level is monitored by reading a staff gauge mounted in the North Cove area of the lake.   The City monitors the lake levels several times each week throughout the year.  This information is recorded along with the current elevation setting of the weir.   This information is critical during the early spring and late fall months when the weir will often need to be adjusted to lower the lake levels to handle anticipated rainfall events. Snohomish County maintains a data collector that monitors the lake level and can be accessed here. Snohomish County Water Data Viewer

Lake Levels

For Lake Stevens, the target level has been set at 211.7 for the summer months of the year, which is 0.1 feet above the top of the weir when at its maximum height (211.6).  This will ensure sufficient flows in the outfall channel to sustain fish passage.  It has been observed that during the dry summer months the lake level is typically lower than the weir height.  The decrease in lake level will provide available storage volume during the wet seasons.