You don’t have to be Isaac Newton to predict that water runs downhill with the force of gravity, often taking loose soil along with it.
In recent history the Idaho Transportation Department learned the gravity/water/soil lesson on Horseshoe Bend Hill, forcing the relocation of Hwy 55 to its present location.
Same issue caused massive rockslides and road closures below Warm Springs Mesa near the golf course as saturated earth caused rockslides on Warm Springs Ave. when it was also Hwy 21. GROWTHOPHOBES will tell you foot hills development is a slippery slope at best.
Seems there isn’t much in the way of “institutional memory” when it comes to Boise foothills road and home construction. The “Boise Front” is essentially the same piece of land as HSB Hill and Warm Springs Mesa, yet Boise City officials seemed surprised that high-end real estate along Table Rock Road is now slip-sliding a way.
For perspective, think of the foot hills as a giant sponge and all the roads and rooftops as strips of plastic wrap. The sealed parts of the sponge repel the water, but soon there is more water than the sponge can absorb and it either pools or runs off like a flash flood.
It may be nice to look down on your neighbors, but those big roofs, paved driveways and roads all tend to concentrate water and saturate the subsoils. The local precip is about 13 inches annually, but all those green lawns and trees at luxury homes need much more water to survive. We know instances of hillside irrigation flooding downhill neighbor’s basements. The laws of gravity are enforced by Mother Nature.
A Boise City spokesman recently told the STATESMAN that policy “requires a licensed engineer to conduct surveys of geological characteristics for the ground beneath every Foothills development. The city requires the same geotechnical surveys for each lot in a development. The city then hires third-party engineers to review the survey reports for accuracy and potential problems.”
“Every Foothills development also requires a grading plan, the extent of which depends on the results of the surveys. The same step is required for each lot.”
A home previously worth hundreds of thousands of dollars and a roadway are now unusable, “baffling the experts.” Could it be the geologists have rocks in their heads and the hydrologists have water on the brain?