Canvas Animation - SetInterval On Update

I'm new to Javascript, and having an issue with getInterval. For my programming languages class we have to create a simulation of waves breaking on a shore from above. I've decided to use a canvas object and Javascript for this animation, but am getting stuck on refreshing the frames.

Here is the code I have so far:
var shoreline = new Array();
var waves = new Array();
var canWidth = 600;
var canHeight = 400;
var waveNum = 0;
var count = 0; .....

As you can see, the idea is that each 5-pixel wide node of the shore and wave are stored in arrays so that the position of each node can differ. The wave() function initializes all the required data, and then calls setInterval on update(). The function update() draws the water, shore, and wave, and then updates the wave position node-by-node. Ideally, setInterval would cause this to happen repeatedly, so that the wave would appear to move closer to the shore every 1000ms.

However, this is not the case. It appears as though setInterval is working for one pass of update(), but fails after the first pass. You can tell that this is happening because the wave appears at its starting position, but does not continue to move. I read somewhere that setInterval can be broken by one-time functions, but I'm not sure. If you'd like to see what it's currently doing in a browser, I've hosted it here [URL]. Once I've got this animating properly I can continue my project, but I've hit a roadblock.