HOMEWORK #2

1. Problems 6.5, 6.7 and 8.1 of Komar.

2. Back in Puget Sound We are looking at the same southwest-exposed Whidbey Island beach – under the same storm conditions. Just so you know, S = 20°, with wave characteristics from last time; namely H_s = 4 m, T_s = 6 sec.

We want to figure out what the effect of interstitial sand is on the mobility of coarse material (cobbles) on the beach. Sand plays a key role in the ecology of a Puget Sound beach. It also regulates the dynamics – and causes many potential (unknown) feedbacks. One of the principal effects of the addition of sand is to smooth the beach surface. In fact, when sand contents are of about 0.3, a mixed cobble-sand beach is effectively ‘smoother’ than a pure sandy beach. Assuming all of the kinetic energy of the swash is converted to potential energy, calculate the velocity of the 2%-swash at the mean-water level using the two end-member relationships proposed for vertical runup (R_2%). How does this compare with the empirical relationship described by Figure 6.36 of Komar? Explain the differences in the results and defend your choice for an appropriate swash velocity on a) a mixed beach b) pure cobble beach.