This is a selection from of my book
"The Essential Guide to Overland Travel in the United States and Canada, The Resource for Independent Travel and Camping".
This selection is a very small part of Chapter 19, Driving on primitive trails in different terrains. This selection covers water crossings and is provided to give you an idea of the kinds of information you can expect to find in my book. Please do not copy any material on this web page.
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Copyright 2016 by TeriAnn Wakeman all rights reserved.
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A vehicle in motion pushes the water ahead creating a bow wave at the front of the vehicle. The water level inside the engine compartment is lower than the water level outside as long as the vehicle continues moving forward. You can increase this affect by placing a barrier in front of the radiator opening. A small plastic tarp placed just in front of the grille or a closed cold weather radiator muff can make a big difference in the water depth inside the engine compartment during a deep water crossing.
Ideally you want a small bow wave when crossing deep water. When wading streams with solid bottoms you should be moving at around three or four mph (about 5 km/h)and be in a low enough gear so your engine is in its torque power band. You want to go about twice that speed on a soft sand bottom, when you need to rely upon momentum to get up a steep embankment, or through a momentary deep spot in a fast current. Driving fast through a crossing creates a high wave that impresses the photographers but is likely to leave you dead in the water and in need of rescue. A word of caution at water crossing photo opts. People like to have their headlights on while throwing water as high as they can for the camera. Headlamp glass can get very hot and may crack if suddenly hit with a solid wall of cold water. Take the crossing slow and get across.
Avoid stopping when in deep water. Within a second of stopping, the water level inside the engine compartment will rise to the level outside and may drown the engine. Exhaust pressure keeps water out of the tail pipe, mufflers and catalytic converter. These areas will flood if the engine stops running in deep water. If you absolutely need to come to a halt in deep water shut off the engine before you stop and get towed out.
Just before making a deep water crossing it is a good idea verify that any special wading gear is in place, that you have a cover over the front of the radiator opening, the fan belt for a mechanical fan is loose or an electric radiator fan is switched off, and that important or easily water damaged items inside the vehicle are located in a high place. Secure one end of a tow strap to your vehicle’s tow ring in the direction from which you are most apt to receive a tow and secure the free length somewhere it will be above water and out of the way during the crossing. This will save you from having to feel around underwater for a tow point if your vehicle gets stuck.
Water crossings are always easiest when you are not the first vehicle in a group to cross. If you are in a group and unsure about the crossing let other vehicles go first. Always pay careful attention to where the leading vehicles plant their wheels and how they fare. If they have trouble and you cannot see why by reading the stream it is best to get out and walk the stream to get a feel for it. If you are alone at a deep crossing with no one to pull you out I strongly recommend that you walk the crossing first to learn the depth and get a feel for the bottom.
When making a deep crossing it may be best to think of your vehicle as a very leaky boat on wheels. If the water gets deep enough your vehicle will tend to float. This means less traction to your wheels which can cause your vehicle to lose forward momentum. In addition the flow of water will be trying to push your vehicle downstream. Making a deep water crossing broadside to a strong current is probably the most dangerous thing you could do when trying to cross a body of water. Whenever making a crossing in a fast current deep enough to put the vehicle body into the water you should make the crossing at least 45 degrees downstream a to the current so the current helps you get across. Never attempt a crossing in a fast current that is deep enough to possibly cause your vehicle to become buoyant.
Reading the water:
The old adage of still waters run deep is indeed true. The surface of the water can tell you a lot about what the bottom is like. That and the shape of the stream bed at your proposed crossing point can give you a good idea of the bottom. Anytime you have any doubts about the crossing, especially the depth, the best thing to do is wade the crossing on foot before driving it. The depth of very clear water can be deceiving and is almost always deeper than it appears.
A flat water surface tells you that either the water is deep or the bottom is flat sand or silt. Be very wary of driving through a section of water with a flat smooth surface. If you are the first or only vehicle at a flat surfaced water crossing you will want to walk across first to verify depth and bottom type before attempting to drive across. If the current is sluggish the bottom may be silt which will not support vehicle weight and may quickly sink the vehicle to the frame. Unlike wet sand above water, sand underwater does not hold vehicle weight well. If you are going to cross a sand bottom it is best to go diagonally down stream so that the water current will help move the vehicle along and keep your momentum up during the crossing. You will want to choose a gear that keeps your engine’s RPM well within the power band without going too fast for conditions. Do not under any circumstances attempt to cross a silt bottom.
An even rippled surface normally indicates shallow depth with a gravel or rock bottom. The smaller and closer together the ripples are the smaller the rocks along the bottom. This is your ideal surface for a crossing. Larger ripples usually indicate a bottom of larger rocks that should be explored before crossing.
A large stationary water bump indicates a large submerged obstacle that could cause undercarriage damage or hang the vehicle up during a crossing. The water is always deeper directly behind the standing bump. Avoid driving into or behind one.
When a stream bed is straight it is normally shallow towards each side and deepest towards the middle. The slope is usually gradual. However differences in stream bed composition such as rock formations may create steep drop offs. You can usually read these changes from the shape of the water surface.
A curved stream bed is always deepest along the outside curve bank and shallowest along the inside curve bank. The stream bed on the inside of a curve is often shallow and gently sloped for about half of the stream width. The outside curve shoreline will have a steep bank sometimes even approaching vertical. Usually the water will be deepest at the sharpest part of the curve and to the rear of it. If you have to cross a stream at a curve try to cross upstream of the sharpest part of the curve and make sure you have momentum going into the deep outside curve area.
If you need to travel up or down a stream or shallow river read the surface and the shape of the stream as you drive. Keep to the pebbly water surface wherever you can. Stay away from the larger standing waves. Stick to the side of the stream when it flows straight and take a stream curve on the inside. Do not enter a sluggish silt bottom stream, pond, or lake. Silt is only semi solid and will not support the weight of your vehicle. Vehicle recovery from silt can be very difficult at best.
After the crossing
During moderate and deep crossings water will get into tie rod ends and U joints. It is a good idea to regrease all these joints within a day or so after a water crossing. Water can get into gear oil reservoirs such as differentials and gearboxes during deep crossings as well. Water can cause damage to these assemblies over time. It is best to check for water in the oil afterwards. Water mixed with oil will resemble a light brown sludge. An easy way to check for oil mixed with water is to open the fill plug and use an improvised dip stick to draw out enough oil to check for color. If you find water mixed with the oil drain the oil into an empty can and refill with fresh oil. If water mixes with gear oil and the vehicle gets parked for a time the water will separate and settle to the bottom causing metal parts immersed in the water to rust. Water vapor will also condense on metal parts above the oil level causing parts above the oil level to rust as well. It is always a good idea to replace oil that has water mixed in sooner rather than later.
Engines that have stalled during a deep wade should be restarted very carefully to avoid damage. First remove spark plugs or glow plugs from the engine then spin the engine over to get rid of any water that may have entered into the cylinders. Replace the plugs making sure that they and their connectors are dry.
Check for water in the oil sump by removing the dip stick and checking the color of the oil. If you suspect water, drain the oil into your empty catch can and replace with fresh oil before trying to start the engine. You will also need to replace the oil filter before attempting to restart the engine. It is always a good idea to carry a spare oil filter, enough oil for an oil change, and a catch can to transport used fluids to a place where it can be safely disposed.
Try to start the vehicle. If it does not start reexamine and dry connections in the ignition system. If your engine has a distributor, remove the cap and dry it out if the inside has become wet. If the engine is computer controlled check the sensors very closely. It could be that you will need to swap out sensors and controllers one at a time to find the damaged part. A broken crank angle sensor is usually the most common culprit. There is a reason why modern engines tend to have a low specified wading depth.
Crossing storm flooded washes or roads
About three quarters of North American flood deaths are the result of people attempting to cross flooded roads in a motor vehicle. Flood waters flow much faster than streams you might be tempted to cross. Do not feel safe just because you have a high clearance 4X4. If the flood water is high enough to reach the bottom of your vehicle’s body it will be strong enough to force your vehicle downstream and likely cause it to roll over in the process.
I strongly advise that you stay out of fast flowing flood waters unless you are absolutely certain that the depth is below your vehicle’s body level and that the surface below will support your vehicle without sinking or hanging it up. Even then think twice and always err on the safe side. Some states have a “Stupid Motorist law”. These laws allow the state to recover the costs of rescuing motorists who get into trouble by doing something stupid. These laws expressly include driving through flood waters. The cost of rescues can exceed $100,000 if both ground and air rescue teams are involved. Your vehicle will be left behind until after the water recedes.
Paved roads that get flooded often become eroded or undermined. Never trust the pavement to still be there during a flash flood.
Never walk a fast flowing flooded section of road to determine the depth and bottom. The second highest cause of flood related deaths is from people trying to walk across flood water. If at all possible seek out a different route or settle in and wait for the flood waters to recede. Flood waters tend to recede quickly once the rain is over.
Tips for Treading lightly in water
In arid regions avoid driving through seasonal streams when water is flowing, small springs, and small water ponds. These seasonal bodies of water support delicate ecosystems that live in the mud or carry out part of their life cycle in these seasonal ponds. Crossing these bodies of water will damage the local ecosystem. Don’t forget standing waters tend to have deep fine sediment that cannot support a vehicle’s weight.
Try to avoid muddying waters that salmon and trout spawn in during the spring. Silt carried downstream can bury the fish eggs and kill them. Coarse gravel, flat rock slabs, and small river rock bottoms not only provide the best support for your vehicle as you cross but produce the least amount of silt.
When you are passing through an ecosystem you are visiting places where native life can easily be damaged by an act of ignorance or a thoughtless act. It is up to each of us to minimize our impact on an ever more crowded world.
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