Some of the tools I use or have used for planning my trips.
Vital information for any paddling river trip.
Some states in Australia provide free current and historical data for many of the rivers. Data from the other states does not seem to be freely available. The Murray Darling Basin Authority also provides historical data for many locations in the basin. The Bureau of Meteorology (BoM) also provides current river flow and flood watch data.
Once you have the data, I like to get the monthly quartiles to see how the river usually behaves. In Australia we have just had two decades of reduced rainfall and it is a trend that seems to be staying around. As such the recent data appears to be more meaningful than the older pre-2000 data. I tend to just use Excel and a box and whisker plot (or just box plot) provides a great way to visualise the data. I usually use the 95% percentile rather than including the flood events that obscure the data.
If dates of previous trips are known, you can correlate the flows and the paddlers account, allowing you to estimate what could be low, good or high flows.
Less of a tool and more of a resource to get up to date and historical images.
The first main use is to find the actual river path as it crosses the landscape. This allows for more accurate distance estimates (see below) as well as possible shortcuts.
You can also look at various lake levels at various times, allowing you to estimate the lake lengths. For example, Lake Hume is approximately 50 km paddle if full and you paddle it in a straight line, or a 85 km paddle along the old riverbed if it is nearly empty.
For rivers with erratic flows, historical images can show the extents of the floodplains when coupled with the river gauge data. This can allow you to determine what channel is best to take in what flow.
These are also a way to assess possible camping locations in relation to the location of homesteads or other features that are best avoided if you have to find somewhere to covertly camp.
The final other main usage I get is to locate possible dangers. These can be weirs, levies, strainers (downed large trees). and potentially mining or industrial sites that could have access issues.
I used a variety of methods calculating distances in the past. The first was a simple length of string. Before starting, I would use the map scale and a pen to mark distances along the length of the string. Then you simply overlay this along the path of the river on an actual physical map. Simple and fairly accurate but you require physical copies of the maps.
The next method I used was with the Google Maps measurement tool as well as the Distance - Find My Distance app by myice92. (Google Play / App Store). You simply trace the river and keep track of the distance.
Eventually I found the excellent open source QGIS project. You can use a variety of image sources and trace the various vector layers, exporting these in a variety of formats for your GPS unit or for embedding the information online in interactive maps. QChainage plugin provides an excellent way to generate mile markers automatically too.
Google / Bing / OpenStreet Maps can be both your friend and your worst enemy. Many tracks, roads and other trails have been entered in from various maps and satellite imagery. These can be cross-referenced with topological data and accurate distances, elevation gains / losses and even rough times can be pulled out of the data. Heck you may even get a bird’s eye view of things. However, many of the more obscure and or remote roads / tracks may not even exist. If in any doubt cross reference with two or more other sources.
Finally, real distances on smaller rivers & creeks are likely greater than suggested in any official maps, as seen in the animated GIF showing the differences in the Australian National Topological Map and the actual aerial photographs. This is from the Condamine River, between Kilarney and Warwick. The actual distance was nearly 50% longer than the drawn river's length!