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Introduction

The Mobile Tensaw Delta is a wilderness like no other. Often called America’s Amazon, it is a 300 square-mile, braided labyrinth of rivers, bayous, creeks, and marshes (Fig 1). The Delta is inhabited by water moccasins, alligators, and feral swine; however, on this canoe expedition, extreme weather was our challenge.

Figure 1. Partial aerial view. Mobile Tensaw Delta. Photo courtesy of Google Earth Pro

In March 2022, on day 2 of a five-day Wilderness Medicine senior elective canoe expedition, weather forecasts called for afternoon thunderstorms. We rose early and struck camp to make our day’s required distance. Our goal was to avoid rough water caused by wind. On arrival at our campsite, we rapidly set up tents so that we would be prepared for the change in weather. We felt safe riding out the storm in a campsite we’ve used many times previously, and could not have known about the tornado that would be spawned later that evening.

Our campsite was a forested, sandy berm adjacent to the Tensaw River and one of the few high ground campsites available in the lower Delta. The river is wide and long there, and south winds soon created waves we could not traverse by canoe, forcing us to stay put. To make matters worse, the wind exacerbated the rising tide, and portions of our campsite soon became submerged.

As we waited for the storm, we gathered a good supply of firewood and cooked dinner. Shortly before dark, the skies cleared briefly, and our group relaxed. Heavy rains quickly dashed our high spirits, and we moved into our tents. Soon the warning signals sounded.

At 9:47 PM a chorus of tornado warnings (Figure 2) blared from campers’ cell phones. Not long after, a student approached the expedition leader’s tent asking what to do. As her flashlight cut through the dark, we realized we were in the projected path of a tornado and had no proven answers for her.

Figure 2. Tornado warning. Photo courtesy National Weather Service.

Our crew was on an island of sand in a swamp forest with rising waters and no buildings in which to hide. Moving to low ground was not an option as it was now covered in potentially snake-infested, cold water on one side and wind and tide driven rushing water on the other. Standard tornado options listed by the National Weather Service were not available.

Figure 3. Topographic map image courtesy US Geological Survey, campsite marked with arrow

We were camped ¾ mile from an elevated CSX railroad line (Figure 3) crossing the Delta. Almost every hour, we heard a train thundering in the distance. It was difficult to determine if what we heard was a tornado or train approaching.

Fortunately, the tornado veered east, and by 1 AM we were listening to the comforting sound of rainfall on our tents as we fell asleep.

This experience proved to us we needed action guidelines for future canoe trips threatened by severe weather. Research shows climate change may be shifting tornado frequency to the Southeastern US, making tornadoes a heightened threat in Alabama.

Professional meteorologist and experienced camper Chuck Doswell provided a 2001 guide for campers caught in tornado conditions. His advice suggested seeking shelter from flying debris “since the majority of tornado casualties are from being struck by flying objects”. Tents provide no protection. Doswell also recommended having something to hold onto as becoming airborne in a tornado is a “distinct possibility”. Doswell’s suggestions were valid, but did not completely fit our scenario.

In our post course review, we noted our campsite was solid and survived the storm without issue. We determined two action guidelines we would implement in tornado warnings. First, mandate all participants wear PFDs during tornado warnings. If swept by winds from our campsite into the water, an individual may have a chance of survival. Second, relocate the emergency locator beacon from the instructor canoe and tie it in its waterproof case to a nearby tree for all to access.

Our canoes were safely pulled up on land, tied together, and anchored to trees. The most significant idea generated was to build temporary shelters from the canoes. The remainder of this article will address this possibility. Readers should note this is an idea that has not been tested.

Build An Emergency Shelter

Most modern canoes are designed to withstand rugged whitewater conditions. Publicity stunts in which two highly regarded canoe manufacturing companies pitched their boats from the roofs of buildings tested impact strength and provided a method to gage the durability of our canoes.

Figure 4. Original photo courtesy Canoe and Kayak Magazine.

In 1979, printed advertisements provided details of the Old Town canoe test in which the canoe landed in one piece (Figure 4). In 2014, Nova Craft repeated the stunt with a 100-foot drop.

We understood application of the terminal velocity equation of a falling object could help determine how much impact from falling objects our boats could withstand. It was relatively easy to obtain the weight of the canoes from the canoe websites. The magazine photo of the Old Town test provided an approximate building height and impact deformation. Watching the YouTube video of the Nova Craft (link above) test showed change of shape on impact when the video was paused.

The Nova Craft canoe, weighing 90 lbs., was thrown from a 100-foot building. From the video, on impact, it appears the canoe bent/compressed approximately two inches before springing back to normal shape (notice the crease in the side, Figure 5).

Figure 5. Canoe deformity on impact. Photo courtesy of YouTube.

Using the equation, the Nova Craft canoe withstood a conservatively estimated force total of 33,000 lbs. For the Royalex Old Town canoe test, we estimated the height of the 4-story building in the photo as 40 feet. Also from the photo, the estimated deflection of bow on impact was 12 inches. Using the equation, the Old Town canoe withstood an approximate impact of 3000 lbs. without damage. From these calculations, it is obvious the modern laminate polyethylene canoes we use are strong enough to handle impact.

It should be noted both Nova Craft and Johnson Marine, Old Town’s parent company declined to comment for this article.

Move Swiftly

Building a temporary shelter with canoes (Figure 6) could be preferable to no shelter at all. We suggest the following actions. Please note, strong ropes will be needed for these tasks. First, fill a canoe with water as a central anchor or base for the shelter. Next, lash the shelter canoes to the base canoe, using seats and thwarts for tie-down points. Then secure the other end of the canoe to weighted food barrels or cook boxes. If available, tie the bow and stern to nearby trees to provide additional security from wind. We believe the base canoe and weighted boxes may prevent the canoe from becoming airborne and provide objects for campers to hold onto.

We tested this theory with two boats, leaning one boat over the other with the opposite end on the ground. We found there was only enough coverage for two paddlers unless both boat ends were elevated (Figure 6). Three boats would be ideal: use two for shelter and one water-filled boat for anchor. Two canoes are wide enough to mostly cover head, chest, and legs. With four canoes, two boats could be filled with water for the base and two used for shelter.

For a single canoe, we suggest finding a downed log or gear to prop the ends over. The ends of the boat must be tied down.

Figure 6. Note: food barrel could be filled with water for anchoring shelter. Photo courtesy of Lynn Yonge.

Can a canoe withstand falling debris from a tornado?

Applicable to tree fall damage is whether the entire weight of the tree falls to the ground. Other possibilities include a tree being partially suspended by incomplete severing of the trunk or the tree canopy dispersing impact of the fall.

Case in point, in a survey of a mature 5-acre forest impacted by a microburst or small tornado touch down during Hurricane Zeta (2020), of 88 trees downed by the storm, 69% of the trees did not completely strike the ground. The full weight of the trees was suspended by a partially broken trunk or the canopy of the tree on the ground, or both (Figure 7).

Figure 7. Tornado downed trees. Photo courtesy of Lynn Yonge

Just as landing on two feet during a human fall will reduce impact, the limbs of a tree can bend to absorb the impact while the number of tree limbs will disperse the impact force. Use of canoes for shelter may also cushion the blow of tree impact by increasing the surface area of contact. The larger the area of contact, the smaller the pressure of impact. Unfortunately, if a tree falls flat to the ground, a canoe shelter may not help. To ascertain the force of impact from a falling tree on a canoe, we needed an estimated log weight. We used a forestry algorithm to calculate the weight of a log.

One 60’ pine tree lying on the ground from the storm detailed above was estimated to weigh approximately 850 lbs. Using the same impact equations, we calculated fall height as half the overall height of the tree. We also used the previously estimated two inches of deflection for the Nova Craft canoe when it hit ground. This equation does not account for energy absorbed by the ground.

If a canoe takes a direct strike from an entire tree described above falling onto the canoe, the impact could be upwards of 150,000 lbs. of force. From our survey of tornado damage in 2020, this possibility seems unlikely. More likely, are falling limbs or partial strikes of the canoe shelter from trees tilting over. In this case, the shelter would provide more protection than a tent. Today’s laminate canoes are built to withstand whitewater impacts. Flying debris should be easy for a boat to handle as seen in this YouTube demonstration of material strength for Nova Craft Canoes.

Conclusions

Our expedition was fortunate the tornado veered away. If faced with these circumstances again, we will have a plan for emergency action. We will place the emergency locator device in a central location, secured to the base of a tree and be certain everyone understands how to operate it. Additionally, we will wear our PFDs during the warning. Finally, we will attempt to build an emergency shelter to protect ourselves from falling debris and flying objects.

The information in this article is an idea that attempts to improve one’s odds of survival if similarly trapped in tornado conditions. It is not a proven method of withstanding a tornado and should not be considered as such.

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