Boat Launch

Lake Water Level

By Mick Steinman/LCIA water level committee

There are two official elevations of Lake Cavanaugh. There is almost a 4 foot difference. The NAVD 88 is newer and higher in elevation. No, the lake is still the same.

The Washington Dept. of Fish and Wildlife (WDFW) has recently received a state grant to upgrade the Lake Cavanaugh boat ramp and parking into concrete ramps and asphalt parking areas. The restroom will be updated to fit handicap standards. The boat launch will be closed during construction during an unknown duration this spring/summer/fall seasons. Current plans are under review by the county permit process.

In review of the proposed changes/plans, we noted an elevation problem with the designed boat launch. This is due to the change in Datum in 1988 as adopted in 1990 by the North American Vertical Datum 88. (NAVD 88)

Below is the explanation of different data in Washington State
NAVD 88 vs Ngvd 29:

Conversion Factors and Datums

Conversion between NAVD 88 and the commonly used NGVD 29 varies spatially; however, over most of the study area the following conversion can be used: NGVD 29 = NAVD 88 –3.6 feet. … Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83) Jan 10, 2013

Ironically the difference in Florida is only 0.5 feet.

The lake level data has been recorded since the 1950’s in the NGVD 29 datum per the Monument located on the boat launch property. The lake level datum monitored will continue as NGVD 29 to keep consistency in data moving forward.

The water level committee has been working with WDFW to make sure that we can launch a boat. The WDFW Datum on their plans is NAVD88. The difference is why on different maps Cavanaugh elevation is mostly noted as 1008 or 1012 Feet.

The lake level per NGVD 29 varies from 1009 and 1015 foot. Winters will average 1011 to 1012 feet and summers at 1009 to 1010 feet elevation.

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