The water is simulated on a 31-meter grid (about 12 million cells) covering the Kern River from Lake Isabella to the west side of the valley. The terrain comes from USGS 3DEP elevation data, which includes the reservoir bed. Filled to the spillway crest, the modeled lake holds about 531,000 acre-feet. The official capacity is 568,000; sediment and the coarse lake-bed data likely account for the gap. Dam outlines come from the National Inventory of Dams via OpenStreetMap. The flow model is a shallow-water solver of the kind used for regional flood mapping.
How the dams fail
Breach size and timing follow the Froehlich (2008) equations, the standard regression used for dam-failure studies. For the main dam, the breach grows to about 700 feet wide and reaches the base of the dam over about 2 hours 20 minutes. If the dam instead gave way almost at once, water would reach downtown Bakersfield about 1 hour 20 minutes sooner.
The storm runs use the Army Corps' published figures. The old service spillway releases 52,700 cfs with 21.5 feet of water over its crest (2,605.5 ft). The 2022 project raised both dams 16 feet and added a labyrinth-weir emergency spillway; together the spillways can release about 506,000 cfs. The labyrinth's crest elevation isn't published, so it is estimated from that capacity. The storm peaks at about 300,000 cfs flowing into the lake, which is below the probable maximum flood the new spillway was built for.
What the city changes
Buildings, pavement and storm drains change how water moves once it leaves the river. The model includes 270,000 building footprints (Overture Maps). Buildings cover about a third of the ground in the densest blocks, so they both block flow and leave less room for the water. Ground roughness comes from USGS land cover. Bakersfield sends most runoff to about 200 retention basins sized for a 100-year storm; the model lets them absorb about 2 inches of water across developed land. In the storm runs the basins are treated as already full of rain.
| Main dam fails | Reaches downtown | Deepest downtown |
|---|
| Instant breach, bare ground | 2 h 45 m | 11.5 ft |
| Realistic breach, bare ground | 4 h 05 m | 10.5 ft |
| Realistic breach, with the city | 4 h 25 m | 14.3 ft |
With the city included, the flood front reaches downtown about 20 minutes later, and the water there stands about 4 feet deeper. Streets channel the water and push it farther across the valley. Storm drains and basins absorb about 11,000 acre-feet, around 2% of the lake. They make little difference in a dam failure.