By Bob Twomey
It is that time of year when people will inevitably visit these powerful natural features, to awe at their beauty, to photograph them … and for some, to be hurt or killed by their unsuspected dangers. It is only May as I write this article and already there have been waterfalls accidents in western North Carolina.
Each waterfall is different. Some are on small streams, others on various sizes of rivers. Some have shallow, broad flows (see Figure 1). Others have concentrated flows over smaller surface areas, which can often lead to accelerated flows of great force, as determined by cubic feet per second (CFS) flow rates (see Figure 2). Similarly, some waterfalls have what is known as “braided flows,” as in the photo showing concentrated flow, whereby the channel water volume is split into multiple channels. This is often determined by water volume and rock shape or irregularities in the rock surface. Concentrated flows are generally deeper and the water velocity is often faster. Based upon rock formation, some waterfalls have vertical drops to pools below (see Figure 3). They may have a substantial drop or they may have a drop of a few feet but have in common no contact with the rock surface during the “free-fall.” Each is different and each has its hydraulic characteristics.
So why would someone in rescue think to analyze a waterfall? After all, a waterfall is a waterfall, right? Well, yes and no. Over 48 years of working with rivers and streams in my former career with the Natural Resources Conservation Service and rescue, I have learned a few things about water flows, rivers …and rescues therein. Sometimes the things I will share with you here, at least in waterfall rescues and recoveries, were learned the hard way. Experience can be a stern teacher about things in nature; a determined rescuer will learn from course work, training, and then practical evolutions and real rescues….so that each subsequent rescue in a waterfall setting will be safer and hopefully easier.
First is river flow. The volume of water flowing down any given channel is measured in CFS (see Figure 4). One cubic foot of water contains 7.48 gallons; therefore, a creek with a 1 CFS flow is flowing at 7.48 gallons per second. A flow of 10 CFS would be 74.8 gallons per second, and so on. However, a river channel is not perfectly dimensioned or said another way, the channel is not square with 90-degree sides and bottom like a concrete drainage canal would be. Thus, even though the flow rate past a certain point might be 74.8 gallons per second, parts of the channel flow are deeper than other parts due to the irregularly shaped channel. This deepest part of the cross-section of a channel is called the thalweg. Friction between the flowing water and the rock surface and edges of the channel will cause slower flow and with less force than the flow in deeper water.
The thalweg, being the deeper part of the channel cross-section, therefore, has more force, or more powerful flow, than the shallower sections. This area is particularly dangerous to rescuers due to the power exerted upon the rescuer within this section of the channel. Also, rescuers MUST always keep this concept in mind: for every 1 cubic foot of water displaced by the body as one proceeds into deeper water, 62.4 lbs. are subtracted from the rescuer’s body weight, since 1 cubic foot of water equals 62.4 lbs. So now, a 200 lb. rescuer displacing 1 cubic foot of water now only weighs 137.6 lbs. The force of the moving water will ALWAYS move a lighter object in the flow easier than a heavier object. The lesson here? NEVER go into moving water without a secure rope anchor system attached to you if you’re in the water current on any waterfall.
So now you have the concepts and interrelationships of water volume, flow velocity, and displacement by your body in water. The deeper you proceed into the flow, the less you weigh and the more force there is exerted upon your body, (which is now lighter than your weight on dry land), and the faster the flow (see Figure 5). In this photo example, the victim or rescuer will still fall to the bottom of the falls once you start sliding. But IF you must move down this waterfall, in a very careful rappel in the water, the obvious choice is in the foreground where the water is only inches deep rather than in the thalweg, which is several feet deep and flows many linear feet per second. And yes, over the years, we have had to rappel down the face of waterfalls to reach victims snagged on trees or rocks in the waterfall itself. Some waterfalls have what is known as a “braided flow”, that is, split flow channels around rocks or vegetation within the “channel.” (see Figure 6). These are falls where rappels through the water and on wet rocks will be needed.
Next is the “biological component” of waterfalls. Algae growth on rock surfaces is very common, even on rock surfaces that are underwater, as in a waterfall. Many things contribute to the types and amount of algal growth on rocks, but the most common are the rock mineralogy, the dissolved nutrients in the water itself, the amount of sunlight that reaches the rock surface, even when submerged under water, the average water temperature in the seasons of the year, and the aspect of the waterfall relative to the sun.
“Aspect” refers to the direction the waterfall faces, as to whether it faces to the south, west, east, or north. This has a great bearing upon the intensity and duration of sunlight reaching the face of the waterfall, which has a significant influence on the light available to stimulate algae growth. I have performed recoveries in waterfalls where the algal growth on the rock surfaces was slicker than ice! This adds a whole new dimension to rappelling access to the victim as well as rigging and recovery. In general, south and west-facing waterfalls receive more sunlight for longer periods of any day, usually enhancing algal growth. However, the rescuer should ALWAYS keep this concept in mind: waterfall rock surfaces will almost always have algae growth on them.
Why is this important? If you are rigging rope access from above the victim, it is prudent to rig in such a fashion that you are directly above the victim to the extent possible. Lateral movement on very slick rock surfaces will be extremely difficult, if not impossible. What if there is not a readily available and suitable anchor above the victim? Then you must make one, which very often requires the rigging crew to become very creative. This right here is why I have said in my articles over the years that you MUST know your equipment and its limitations when used as anchors. The forces generated upon anchor slings (generally two-inch tubular webbing) when rigged at certain angles have great bearing upon the forces applied to these slings. The way the anchor is composed is likewise crucial, such as in the preferred use of load-sharing, and self-equalizing anchor systems. ALWAYS rig your anchor systems with “redundancy” whenever possible. Should one anchor fail or should one “leg” of the anchor system fail, the rest of the system can shift (self-equalizing) and equally “load” the remaining legs (load-sharing) without danger of overstressing them…and you don’t go to the bottom of the waterfall yourself. That would probably not be good …
If no suitable anchors exist directly above your victims, such as rocks or trees, you will have to create an anchor rope across the top of the falls to which all your riggings are attached. This would be like a Highline system but it is loaded more horizontally than vertically. This is acceptable if your “side anchors” on the banks of the river or waterfall are strong. This is where knowing the tensile strength of your rope and the load-bearing capabilities of your mechanical devices is paramount. A rescue spotter is usually very good to have. This rescuer should be able to see the entire situation from a distance and guide the rescue team to the location directly above the victim via radio.
Then comes the fun part, where you must access the victim. On some waterfall rescues, you will have to rappel through and with the water as it cascades down upon you. If you have never had to do this, with hundreds of gallons of water per second cascading down upon you, you have missed something … I think. ALL gear becomes soaked in a few seconds, you get to find out if your radio is waterproof, and you learn very quickly how well-wet rope and braking devices work. Rescuers should know how their gear works when saturated. Likewise, you get to learn how to make sure all attached gear stays attached to your harness because once you are over the edge in the flow, it is NOT easy to ascend your rope. After all, you lost needed gear. Likewise, being comfortable rappelling with a loaded backpack of rescue gear may be new for you. The backpack makes you very top-heavy and subject to inversion if you are not strictly and constantly in control of your descent.
For waterfall rescues, it is recommended that you use class III full-body harnesses. Your body weight plus the weight of water coming down on you can be more evenly distributed over your body with a Class III harness. This will make an hours-long rescue or recovery much more comfortable. You as the rescuer(s) going over the edge should plan on taking what you will need to complete the rescue once you reach the victim. Some waterfall settings simply will not allow the portage or lowering of additional equipment to you. Your boots should not have such a rigid sole that you cannot “feel” the rock surface. Heavy lug boots won’t be of many benefits on slick rocks, even though they may provide good ankle support. The more surface area contacts your footwear has with the rock surface, the better traction you will have on slick rocks. Therefore, quality fishing waders have felt soles: improved surface contact on slick rocks.
The rescue is next. Does your team perform a raise or a lower of the victim? This decision is based on many things, primarily the benefit-risk ratio to the rescuer(s)…and concern for your victim. We didn’t put them there; likewise, we can’t help them if we are busy getting hurt or dying ourselves. How high is the waterfall? How much water flow is there? What access is available at the bottom of the waterfall if we opt to lower the victim? What seems the easiest and is in the best interest of a live victim given their injuries? How long will a carry-out of a lowered victim take? What equipment do you have for raising or lowering a victim? Is adequate manpower available for the chosen option? What time of day is it and how long before dark? What is the expected weather for the duration of the rescue? Is adequate mutual aid available to assist in the chosen rescue method? How are the elements of the waterfall affecting the rescuer(s)? Will water flows change because of upstream operations, as in a hydroelectric dam, and the water requirements thereof?
Many things must be considered by the Incident Commander (IC). Precise, effective communication between all rescuers involved is required. The Incident Action Plan (IAP) must be accurately conveyed and understood by ALL rescuers involved. Once you reach the victim, all previous plans may have to be completely changed due to circumstances. This is where having good radio communications is critical and having enough equipment with you (that you took down with you) pays off. Our squad members have had to perform rescues with only what we took down over the top of the falls with us. These rescues or recoveries are very difficult and time-consuming. Good mutual aid agreements with skilled rescuers are important, as is preplanning on at least certain popular waterfalls in your area.
At the very least, I hope this article opens your eyes to the many dangers and considerations a rescue agency must know (not just consider … but KNOW) about waterfall rescues. All the skills from numerous disciplines will be required, especially rigging and high-level rescue. What it will always come down to is this: train, work hard, continue to gain experience … then just do it.
Bob Twomey has been in the volunteer rescue service for 46 years, having served on five Rescue Squads from the coast to the mountains. He is currently a member of Transylvania County Rescue Squad, past Chief and Training Chief, an EMT for 45 years, and is an IFSAC and OSFM certified Rescue Instructor. Bob has been active in SAR, Mountain Rescue, and teaches high-level rescue. He is the chief pilot of Wolf Tree Aviation, and flies helicopter searches and rescue support locally. He is a Crew Chief for the NC Forest Service. He can be reached at 828-884-7174 or at email@example.com.