*3.2. Hydraulic Model*

After the weight and density of a banded-rhyolite sample is determined in the laboratory, a hydraulic model may be applied to predict the energy needed to shift larger rhyolite blocks from the headland outcrop and deposit them as a CBB in Ensenada Almeja. Along with shape, size and density, the pre-transport environment of coastal boulders factors into the wave height required for detachment and removal. Boulders derived from a weathered surface with deep joints at right angles are influenced mainly by lift force, alone. This requires somewhat higher waves to initiate transport compared to boulders already siting in a submerged position. To initiate motion of a loosened block, the lift force must overcome the force of restraint minus buoyancy, provided the block has separated completely from the basement substrate. Herein, the general formula used to calculate wave height related to CBB development is taken from the work of Nott [13], used for estimation of storm waves.

$$H\_s \ge \frac{\left(P\_s - P\_w/P\_w\right)^{2\alpha}}{\mathcal{C}\_d \left(ac/b^2\right) + \mathcal{C}\_1}.$$

where *Hs* = height of the storm wave at breaking point; *u* = (gH)0.5 and ∂ = 1; *a*, *b*, *c* = long, intermediate and short axes of the boulder (m) *Ps* = density of the boulder (tons/m<sup>3</sup> or g/cm3), *Cd* = drag coefficient, *Cm* = coefficient of mass (= 2) and *C*1 = lift coefficient (= 0.178);

> *u* = instantaneous flow acceleration (= 1 m/s2)

A variation on this formula applied exclusively to joint-bounded boulders is as follows [13]:

$$H\_s \ge (P\_s - P\_\text{w}/P\_\text{w}) \text{ a/C}\_1$$
