There are numerous reasons why we monitor rivers and countless ways in which we undertake that monitoring. Here is a brief and incomplete list of links to sites and/or publications on monitoring tools and some methods. I add to it as I stumble across things or think of something useful. It is rather biased towards geomorphic monitoring.
WORK IN PROGRESS
Map Grade GPS
The Wolman Pebble count is probably the best known traditional method of measuring sediment in gravel bed rivers, but many other techniques exist. Bunte & Abt (2001) is an incredibly comprehensive overview of such techniques.
As much as we all love manual labor and brute force sampling techniques, automated methods are a viable alternative in some circumstances and can save a lot of time. For example Sedimeterics
is one of several groups that has developed software to allow you to extract grain sizes from digital imagery. In their photo at right, they show someone snapping an image of and exposed gravel bed, which then is plopped into their software and spits out a grain size distribution and various stats.
Measuring Sediment Transport
Remote Sensing Imagery
Time Lapse & Motion Activated Photography & Video
Rees River at SH Bridge from Damia Vericat on Vimeo.
See River Rees Webcams here.
Topographic Survey Instruments (ground-based)
I am admittedly biased here. I have used extensively equipment from Topcon, Trimble, Geodimeter (now Trimble) and Leica. I have to admit I am very partial to Leica Equipment and that is what et al.
Leica Total Stations
Topographic Surveys (remotely sensed)
Green LidaR (Bathymetric LiDaR)
Traditional Airborne LiDaR
Airborne LiDaR has become widely available both as publicly available datasets in particular areas, and a monitoring tool which can be commissioned from private vendors and research institutions.