River Crossing
From WildWiki
Contents |
River Crossing and River Features
Mountain travel requires the ability to judge moving water hazards and execute safe river crossings. Water travel may require river reading for linings and portages.
Educational Goals
Students need the judgment and skills necessary to cross moving water without supervision. They should be able to recognize and asses river hazards; they should know when dry crossings are appropriate and when it is better to wade; and they should be able and willing to decide not to cross a river if conditions are too difficult.
Key Points
River Features Study the river. Current-or the speed of the river- is determined by volume, depth, width and gradient. As a river widens, the current lessens. As the river gradient lessens, the current eases off. Narrow channels can have faster water.
An eddy is a slow spot in the current formed behind obstructions. It is sometimes possible to eddy hope-or move from one eddy to another- to avoid having to tackle the main current for extended periods of time.
The deeper the water, the slower the current must be to wade. Visibility can help you determine how deep a crossing will be. In general, visibility declines with depth. If you cannot see the bottom chances are the river is too deep to wade. Surface texture also provides a clue to water depth. Deep water is glassy and masks the river bottom. Foaming rapids occur where the water is shallow, the gradient steep, or there are boulders and other obstacles along the river bottom In glacial streams or silty rivers, visibility is not as good assessment method. Throwing rocks and listening for contact with the bottom may help you gauge depth.
To gauge water speed, throw a stick into the main current and walk next to it on the bank. In thigh-deep water, most people cannot cross if the current is moving faster than they can walk. Because a backpack increases your surface area and catches more of the current power, wearing a pack will further inhibit your ability to cross deep moving water.
In mountain regions the warm temperatures of spring and early summer may raise the river to flood levels and increase the chance of logs and debris washing downstream. The likelihood of coming upon strainers – or trees and logs lying partially on the bank and partially in water – also increases in flood stage. Strainers trap objects which wash down with the current. A person who gets caught in a strainer can be pulled under and pinned against the branches which extend down into the water.
Water levels rise as the day gets warmer and snow melts, and then drop back to their diurnal low between sundown and sunrise when melting slows. You can expect a mountain river fed by snowmelt to come up quickly when the weather gets warmer. Temperature increases also weaken snow bridges across rivers.
The river bottom plays an important part in where to cross. The chance of getting a foot trapped or having a wader trip increases with the size of the rocks on the bottom. Sand often covers rocks and logs in slow moving water and makes crossing easier.
Water plunging down a steep gradient is likely to be fast and tumble rocks along the bottom. Listen for these potential ankle breakers washing down before stepping in to cross.
For entrances and exits, look for river banks without undercuts, overhanging vegetation, or steep slopes. Consider what would happen if you fell and got swept downstream. Bad washout zones include waterfalls, strainers, rapids, and low-hung snow bridges.
Scouting Take time to find a good place to cross. Scouting is best done with your pack off. Examine the map to see how large or steep an area the river is draining. A river draining a south facing alpine basin or glacier may have more flow than a shaded north-facing one. Maps can also give you clues about gradient, river width, tributary locations, and wooded areas. Use high ground to survey large sections of the river.
You may need to scout a long way up or downstream in search of a shallow, wide place where the current is manageable. Consider crossing the river’s tributaries or feeder streams where the water volume will be less.
Crossing Methods River crossings can be divided into two basic types dry and wet. Dry crossings include logs, rocks, log jams, and other natural bridges. Wet crossings mean wading.Your students need to understand the consequences of a slip before crossing. Ask them what would happen if they fell? Will it result in a wet foot? Lost equipment? A broken bone? Drowning?
Less able group members may need help with their loads. Consider using the stronger and longer-legged people to shuttle packs across. Ultimately, however, everyone needs to feel comfortable about the site before you commit your entire group to the crossing.
Dry Crossings Crossing on logs, rocks, or using the high step technique preserves dry feet, but often requires balance, agility, and luck. Failure to execute these maneuvers properly is more likely to cause injuries than a carefully thought-out and well executed wade.
Fallen trees and log jams can be used as bridge. Choose logs that are stable, broad and dry. Avoid crossing on thin, slippery or inclined trees. Consider setting up a hand line to aid balance. Place the line at shoulder height and off to the side so that it does not interfere with packs or walking. Examine the consequences of falling off the log on the upstream side. The log may be a strainer.
Log jams are tempting foot bridges, but unless they consist of large, well-anchored trees that span the entire river, view them with suspicion. The entire pile may be held in place by one or two key logs that may shift or release if someone walks on it. This can be especially dangerous when they are in the main current. If the jam shifts or moves, find another place to cross. A hiker who falls through these floaters can be pinned by the current.
Crossing on rocks is another option. But before you start jumping from rock to rock, rehearse your sequence of hops and steps in your mind. Try to connect dry, flat and closely spaced rocks. Have your students imagine the rocks are coated with ice, so they place their foot on them delicately. Smooth, continual movement facilitates balance.
If you fall when rock hopping you can bash yourself on rocks or even drown. Knee injuries may occur when the leading foot slips and the momentum of the leap continues to carry your knee forward onto the rock. Use a stick or a long fly rod case to provide balance while stepping from one rock to the next. This often reduces the need to leap, allowing more secure and balanced movements. And remember, we do not encourage boulder hopping with heavy packs on dry land, therefore, we should not promote leaps onto the slippery and rounded surfaces found on river rocks.
Wet Crossing Prepare for the crossing. Practice and familiarity with challenging wading conditions is important. Get your students out in a river with out their packs, trying different methods so they recognize the strengths and limitations of each crossing method before they have to use them. Have them try using a stout stick or the arm of another group member for added balance. Get them to feel the force of moving water so they respect its power and understand what method of support (stick, hand holding, grasping packs, etc.) is most comfortable.
Consider practicing your crossing positions on dry land or in shallow, slow water. Keep your feet shoulder-width apart and avoid crossing them when you walk. Use your foot to feel for solid footing before weighting it and commit carefully to each step.
Redistribute loads to avoid top heaviness. Face upstream so the current won’t buckle your knees. Avoid starting at the river; moving water can mesmerize you and interfere with your balance. Choose a line that angles downstream if you want to fight the current less.
Wade in boots to provide adequate ankle support. Remove your socks, insoles and gaiters then lace the boots up tightly for support and security. If you are wearing plastic boots and plan to wade in just the shells, you’ll need to keep your gaiters on. Gaiters help prevent the boot shells from washing off your feet. Sometimes it is helpful to wear socks to pad your feet and make the boots fit more securely.
For deep crossings, consider removing wind pants and long underwear so there is less drag against your legs. Clothing can balloon up with water, which may make it difficult to move. Make sure all loose items are secured inside your pack. Keep your hands free and avoid dangling things around your neck. Loose items will be the first things to disappear if you fall in. Have the largest, most experienced person or team test the current prior to committing the entire group. Test it without packs on. If the test group encounters trouble, consider wading elsewhere.
Consider the possibility of hypothermia from any combination of factors such as a long crossing in cold water, someone falling in, multiple crossings to shuttle packs or help less capable students and adverse weather conditions. Cross with wool hats, extra upper body layers and long underwear (understanding the concerns listed above0. If possible have stoves on either side of the river.
Be prepared if someone should fall. Post spotters down stream to help anyone who falls and is carried by the current. Spotters should stand along the river’s edge near eddies where swimmers are likely to be carried. They should be prepared with long sticks or other items to use to help someone out of the water if necessary.
Be aware of any downstream hazards such as rapids, waterfalls or strainers. Anticipate needing to remove your backpack while floating downstream in cold water. Unfastening hip belts and sternum straps before attempting the crossing should make this easier, though not always. There are situations where leaving hip belts fastened may be acceptable. These decisions require experience and judgement and you should expect that most novice students do not have enough experience to make such a call. Have students cross with hip belts unfastened until they demonstrate competency crossing rivers. Judgment parameters can then be introduced if appropriate.
Balance is the main factor in deciding whether or not to have hip belts fastened. When performing dry crossings, balance and pack stability are integral to success. Redistributing weight in the pack to avoid top heaviness and / or keeping the hip belt fastened may be useful. But if in a fall in this situation would result in being swept away or landing in deep water, unfasten the hip belt. In a wet crossing, if you need to face upstream for balance, or if the water is at or above your knees, unfasten hip belts.
How Deep Can You Wade Safely? - Ankle to mid-calf depths usually can be waded singly with a stick or with one other person for support.
- Mid-calf to mid-thigh depths should be waded with two others for support. Crossings become noticeably harder in water above the knees.
- Mid-thigh to waist-deep wadding becomes even more difficult because any current tends to buoy up the waders, especially if the current hits the backpacks. Seriously consider finding a better place to wade.
- Avoid moving water above waist deep. Find a shallower crossing, build or locate a dry crossing, or better yet, change your route.
Wading Techniques There are numerous methods and variations of methods for wading rivers. The following techniques and concept are generally accepted. Other methods may be appropriate given specific local factors.
When crossing on your own, face the current and use a stick as the third point of a tripod.
• Move perpendicularly or diagonally across the current.
• Move one point at a time.
• Use the stick to probe for holes.
• Shuffle across in small steps. Keep the stick in front of you.
• Keep moving. Hanging out in the hard parts wastes energy and increases risks.
Crossing in a team tends to be more stable than crossing alone. There are several methods to use. Experiment to determine the conditions suitable for each technique.
One team method uses two to five people to cross the river in a line parallel to the current.
1. Face the current. The first person wades with a stick. The others line up behind her and grasp the person or her pack in front of them securely.
2. The first person breaks the current and creates an eddy in which the second and third stand. Those in back help support the first person so the current does not push her over.
3. The group moves in small steps together. They work as a tight unit until out of the river.
The group pole method uses a long pole to provide stability.
1. Three to ten people hold a long strong pole in front of them.
2. Grip the pole firmly for more stability.
3. Use bigger teams for more support.
4. Face upstream and move as a team across the current.
5. Get the entire group on land before you release the pole.
Teaching Considerations
River crossings are one of the most hazardous activities in wilderness. It can be hard to instill respect for the forces involved when a person has not felt the impact of water pushing against his legs while wearing a heavy pack. Make sure you know everyone’s swimming ability before teaching river crossings
Even though this subject is strongly governed by common sense, do not assume your students automatically understand the seriousness of moving water. Start talking about river crossings as soon as you encounter a fordable stream. Get them used to having wet boots.
Teach river scouting and crossing organization at the same time. Give your students the criteria for choosing a crossing, send them off to find an appropriate spot, and finish by discussing the merits of their recommendations. This is an appropriate time for the instructors to share their judgement with the group. Make it clear why a particular crossing and method are used or not used.
Model safe crossing techniques, especially for rocks and log crossings, and remember what may be easy for you is often difficult for novices. Let students know that the whole group must be comfortable with a crossing. Strict time schedules may lead students to rush, pressure them into a bad crossing, or prevent them from doing adequate scouting. Communicate expectations which promote wise student decisions-decisions that include choosing not to cross.
In a low water year or late in the season, courses may not get a chance to wade rivers that are exciting and educational. Instructors have been able to teach crossing techniques and water safety by practicing wading at the outlets and inlets of the lakes. Consider practicing wades without packs if you believe the group needs more experience.
Leadership Opportunities
River crossings demand good team work and organization. Find a practice site that is appropriate for solo crossings, as well as one that will challenge people and force them to work together.
Resources Bechtel, Les and Slim Ray, River Rescue, pp 55-60 NOLS Wilderness Educator Notebook pp3.17-3.19
