Table of Contents

1. How to use time of travel charts
2. For what conditions can the time of travel charts be used?
3. How were the river reaches determined?
4. How were the low, medium, and high flow rates determined?
5. How to I obtain current river information?
6. How can I estimate other travel times?

How to use the Time of Travel Charts

The time of travel charts are modeled in the style of road maps which allow for a quick determination of the travel distance between any two points on the map. The same technique can be applied to times of travel on a river or stream given a flow condition.

With a time of travel chart in hand, one can look up the travel time by choosing any two locations and finding their point of commonality.

River mileages are shown along the left and bottom of the charts. Landmarks corresponding to these river mileages are shown from top to bottom along the right hand border of the charts.

In the sample chart number 1 below, the time of travel between the site labeled as Creek and that noted as Bridge is shown as approximately 0:10:00 or 0 days, 10 hours, and 00 minutes.

Sample Chart 1

Given two river mileages, in this case 914.0 along the left vertical edge and 916.8 along the bottom edge of the chart, one can find the river mile for one landmark along the left hand side of the chart and the other along the bottom, then locate the point in common as shown in Sample Chart 2.

Sample Chart 2

Also available in PDF format is an example of how to use these charts.

For what conditions can the time of travel charts be used?

Travel times were determined for open water, surface current, all season river discharges. If other physical elements may be important, the following guidelines are offered:

• Wind: Times of travel at the surface can be affected by wind action. This is especially true in areas where the river is wide and winds may blow material toward and eventually onto the shore. Winds blowing downstream or upstream may have either a beneficial or adverse impact.

• Ice cover: Reduce the time of travel by 10-percent as the bottom of ice friction and resulting velocity profile changes.

• Velocities at other depths: If the average velocity in the vertical water column is needed, use 90 to 95-percent of the surface current velocity. Travel times for materials near the bottom of the river is harder to estimate as depth of flow and the roughness of the channel bottom may vary considerably and is difficult to estimate with any degree of certainty.

• Seasonal variability: Flows are generally low during the winter season after an ice cover is formed. During the spring snowmelt runoff in late March and early April, flow rates are generally higher. Summer rainfalls may produce noticeable increases in flow rates following storms. During the fall and early winter, flows are usually lower than normal.

How were the river reaches determined?

There are 330 miles of river from Grand Rapids to Minneapolis. To make data presentation manageable, continuous sections of river mileage were broken in five sections or reaches. Factors used to determine the various reaches include, but are not limited to: USGS gaging station locations, major geographical features such as dams and cities, and data density.

How were the low, medium, and high flow rates determined?

The US Geological Survey publishes daily river discharges for rivers and streams in the United States. Only those daily discharges marked as Approved for Publication by the USGS were used. For the period of record at each USGS gaging station, discharge data values were retrieved and numerically sorted. By inspection, discharges which fell at the 90, 50, and 10-percent points were then used. The USGS uses the 90, 50, and 10-percent exceedance levels to represent low, medium, and high flows respectively.

How do I obtain current river information?

• USGS Data Collection Platforms (DCP) in place at gaging stations. Hyperlinks to these DCPs are provided in the USGS Data document.

• Hydropower generators and dam operators may be able to provide current discharge values at their facility.

How can I estimate other travel times?

Travel time may be computed by dividing the distance by the stream velocity. Distance is usually given as miles above a given landmark. Stream velocity is usually given in feet per second (FPS). Therefore some unit conversion is required.

1. Determine the river mileages for the points of interest and compute the difference. Call this the Distance in Miles.

2. Get an estimate of stream velocity in feet per second (FPS) from other charts, estimates from field personnel, USGS real time data collection platforms, or some other method in which some confidence can be given.

3. The time of travel in hours can be found by dividing the distance in miles by the product of the stream velocity in feet per second and 0.6818 as follows:

   Time of Travel =	Distance in Miles -----------------------------------
   	0.6818 X Velocity (FPS)

   For example: If the river mileage difference is 10 miles and the estimate of stream velocity is 2.5 feet per second, then:

   Time of Travel =	10 -------------------------
   	0.6818 X 2.5

   The result in this case is 5.87 hours, or 5 hours and 52 minutes

4. The formulae used in these calculations have been incorporated into a web calculator to compute the time of travel between any two river mileages and the assumption of an average velocity between these two points.