Tubing Speed and Depth datalogger

So I was tubing the other day, and the first half of the trip went really quickly, so I figured I would get picked up at the end in about 30 min. However, the second part of the trip was at a near crawl and I had to paddle the whole way.

While I was paddling, I thought how awesome it would be to bring an Arduino along to log the speed of each area of the creek so that one could get an idea of how much time a trip would take.

I could just hook up a GPS and SD card and gather location and speed data every 5 seconds or so, but I would also like to know the depth of the water in each location.

So far, all of the water depth sensors are designed to gather depth in a single location. Is there a "Fish Finder" type sensor that I could attach to the tube to measure the depth of the creek as I float?

Or will I just have to stick with speed data?

I could just hook up a GPS and SD card and gather location and speed data every 5 seconds or so

The GPS typically output data once a second.

Is there a "Fish Finder" type sensor that I could attach to the tube to measure the depth of the creek as I float?

Google "depth sensor". Some interesting ideas...

When I search "depth sensor", I get a bunch of stuff about Kinect or I get the Parallax ultrasonic sensor, which as far as I know will just detect the surface of the water.

I built a speedo for my sailing dinghy last year, using an inexpensive UBlox GPS module. The module spits out the data as a stream of NMEA (csv) sentences which are easily read from the Arduino serial port. The module carries out it's own correlation, providing a speed measurement within the NMEA sentences. Non-augmented GPS derived speed measurements are not very accurate at low speeds though.

For measuring the depth of water, try searching for 'echo sounder' or 'depth sounder' or 'fish finder.' The problem is more difficult than you might think.