Lake Wohlford dam to be studied for quake upgrade

ESCONDIDO – A consultant will study Lake Wohlford's dam to determine how to reinforce it so that it can withstand a major earthquake.

The Escondido City Council on Wednesday unanimously approved a $196,000 contract with Carlsbad-based GEI Consultants.

The city's utilities manager, Mary Ann Mann, said before the council meeting that the bottom part of the Wohlford dam was built in 1895 with rocks, reaching a height of 76 feet.

The concern is that portions of the dam added later could “liquify” in a major quake, causing it to fail. Most of the water in the lake northeast of Escondido comes from Lake Henshaw and is channeled through the Escondido Canal. The lake is a source of water for Escondido and Vista.

The dam worked well until 1916, when rainmaker Charles Hatfield supposedly caused major flooding and Lake Wohlford overflowed, Mann said.

In 1924, authorities added 24 feet to the height of the dam using silt and sand, and reinforced the landward side with similar materials. But the materials were not evenly mixed, Mann said. Although the dam passed state tests in the intervening years, in May the sand-and-silt portion flunked a federal test.

Results showed that the addition could crumble in a 7.5-magnitude earthquake. Since then, the city has kept Lake Wohlford – which can hold about 6,500-acre-feet of water, more than 2.1 billion gallons – at half-capacity so its level stays below the height of the original rock dam, which was shown in the federal tests to be strong enough to withstand earthquakes and floods. Mann said the consultant's report should be completed by July.