Drowning Trap. Focus. Read 10 point text from rear of room. Bottom

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1 Drowning Trap Focus Read 10 point text from rear of room Bottom 1

2 Before we start, please answer these questions: 1. Most fatalities on a river (e.g. Potomac) occur at? Flood levels Moderate levels Low flow (summer pool levels) 2. Most people perceive that a river is most dangerous when which of the following conditions occur? (Check all of those which apply) Water over the banks and into the trees High water Muddy water Big waves Dead cows floating down the river When the river looks normal. 2

3 Drowning Trap: Surprisingly, on the Potomac River people drown at levels well below flood levels; they drown at levels just slightly above summer low flows. Robert B. Kauffman, Ph.D. 7 Hilltop Drive Frostburg, MD h: (301) o: (301) e: rkauffman@frostburg.edu The information contained in this presentation is found in the following technical report: A Recreational Gauging and Information System to Alert Potomac River Users of Dangerous Water Levels. DNR Boating Administration, Planning and Policy Program. Parts of this presentation may be reproduced with appropriate reference and citation. 3

4 Drowning Trap Model - Depth of the River + Velocity + Deceptiveness A trap captures unsuspecting victims... The drowning trap captures unsuspecting river users, users who do not perceive the dangers of rivers. = Drowning Trap 4

5 Topics - Background The Problem - Why Rivers Are Dangerous? River Dynamics Fatalities Drowning Trap Deceptiveness River dynamics User groups Safety issues Summary and Findings. The items on the left provide a general discussion of the topics in this section. 5

6 Background: State of Maryland commissioned a study Mainstem of Potomac River from Washington to Cumberland Study completed in 1992 Studied hydrology Studied fatalities and replicated McCurdy study Studied user attitudes and behavior Determined causes of the fatalities. Thirteen people died on the Potomac during The State of Maryland wanted to know why and what to do to prevent it from happening again. 6

7 When Are Rivers Dangerous?: Ask people when rivers are dangerous and they will usually respond with high water muddy water big waves water over the banks and into the trees dead cows floating down the river, The obvious answer is that rivers are dangerous when they are flooding. Of course floods are dangerous, however, most fatalities occur when the river looks quite benign and harmless. 7

8 Fatalities: The study found that most fatalities occurred not at flood levels and not at summer low flows but at moderate water levels during the summer (Spring flows in Summer) Less than one out of ten fatalities (9%) occur below Drowning Trap level Few fatalities (20%) occurred above Drowning Trap levels (and flood - 16 ) Seven out of ten fatalities (71%) occurs at moderate flows, Conclusion: Most people drown at moderate levels, well below flood levels. Above % Drowning Trap Levels: Between % Below % 8

9 Temperature, Flows & Fatalities: Juxtaposing temperature, fatalities and water levels shows relationship As expected, air AIR TEMPERATURE temperature - and PERCENT increases with the coming of Summer Water levels are high in Spring, then drop in Summer River fatalities parallel air temperature, then drop, paralleling falling water levels, Conclusion: Spring flows in Summer kills people. Potomac River Drownings MONTH Average Monthly Temperature Percent of time flow is between 3.4 and5.2 on Little Falls gauge 9

10 River Dynamics - Laminar Flows Shore to Center Flow Summer Flows Drowning Trap Flows Flood Levels Premises and Assumptions Depth versus Velocity River Profiles. The question is how does a change in river depth affect the power (velocity) of the river and how does it affect river fatalities? 10

11 Laminar Flows: Imagine several sheets of plywood with wooden dowels between the sheets Push the stack Their speeds are additive... With the sheet on the bottom traveling the slowest And each sheet above the bottom sheet traveling faster than the one below it... (continued next slide). SURFACE RIVER BOTTOM 11

12 Laminar Flows: The air slows slightly the sheet just below the surface This creates a depression or void (shore to center flows - next slide) The stack is pushed The bottom sheet moves the slowest, slowed by the bottom The next sheet moves its speed plus the speed of the sheet below it, (3) Conclusion: As depth increases, river velocity increases (see general river velocity). Fastest water is just below the surface SURFACE RIVER BOTTOM 12

13 Shore to Center Flows: Laminar flow in center of an unobstructed channel Slower surface flow creates a slight depression which draws water in from sides to fill the depression (from previous slide) Most likely to occur in drainage ditches and irrigation channels; fastest water is just below surface. 13

14 Normal Summer Low Flows: Gauge Level: 1 foot Time of Year: Summer River has little apparent flow; often seems pool like Vegetation on gravel bar is summer growth of annuals and other nonpermanent vegetation. 14

15 Flood Flows: River is over its primary banks, into trees and other vegetation along the banks Gauge Level: 16 foot Time of Year: Summer River looks like it is flooding. Muddy water, big waves, large objects floating down the river. 15

16 Drowning Trap Flows: Close examination reveals a distinct current. The river is not over its primary banks Gauge Level: 4 foot Time of Year: Summer Summer growth on gravel bar is usually covered with water indicating higher summer flows than normal. 16

17 Assumptions & Premises: Consistent hydrology along the mainstem except Cumberland Compared profiles Same channel, proportional depth and width, just larger drainage areas Gauge readings correlate with each other Point of Rocks used as reference or base point. Cumberland Paw Paw Hancock Shepherdstown Little Falls Point of Rocks 17

18 Velocity - General River: Moving water has power SURFACE WATER VELOCITY (feet/second) Drowning Trap Ranges Maximum At low levels, a one foot change can double the velocity At moderate levels it results in a change of 0.5 feet/second Most drownings occurred between 2-6 feet Velocity Doubles Flood - 16 Relationship is a function of river channel (see profiles) Push over a 5 10 man (next slide and ft/sec) 1foot POINT OF ROCKS GAGE (feet) Average Minimum 18

19 Pushing Over a 5 10 Man: A simple empirical test was done in the Potomac River near Little Falls with a 165 pound man In waist deep water, it takes roughly feet per second to push you over This is 4 on Point of Rocks Gage middle of Drowning Trap flows. In chest deep water, it takes only feet per second to push you over. This equates to 2 on Point of Rocks gage Conclusion: It doesn t take much to move you about feet per second feet per second 19

20 Velocity - Behind a Dam: SURFACE WATER VELOCITY (feet/second) Drowning Trap Ranges Velocity for the general river is shown for comparison Velocity behind a dam, starts slowly and then catches up to general general velocities, Conclusion: You have the same flow problems behind a dam, it starts slower and takes longer to catch up with general river flows. Maximum Minimum POINT OF ROCKS GAGE (feet) 20

21 River Profiles - Impact: River profile of river at Point of Rocks, Maryland (note distortion) Typical summer levels Drowning Trap flows Floods - big, muddy, over the bank, into the trees, cows floating down river Conclusion: This is one reason why Drowning Trap levels are deceptive. GAUGE LEVEL Feet Flood - 16 Drowning Trap Levels: WIDTH OF RIVER - Point of Rocks 21

22 User Groups and Deceptiveness - Four user groups examined: Tubers Canoeists Power boaters and Waders/swimmers They need different management styles. 22

23 Assumptions and Premises: Groups are not homogenous differences between user groups are explainable Total sample size... Sub-sample sizes Canoeists sampled Power boaters includes PWCs. 23

24 Tubers: Well educated (65% college graduates) Younger (80% under30 years old) Three quarters (75%) one time visitors Seek nature, to be with a group, group affiliation They are not safety conscious, Profile: Young, educated fun-seekers who are one-time users. We drink alcoholic beverages on the river (40%) We are all good swimmers, and None of us wear life jackets. 24

25 Canoeists: Very well educated (72% college graduates) Older (67% over 30 years old) Half (50%) visited this site the equivalent of three weeks a year (20+ days) Seek nature, use their skills, obtain dominance, seek achievement, exercise, and use their equipment They are safety conscious, Profile: highly educated, frequent users who test their skill on the rapids. None of us admitted to having alcoholic beverages We all rated ourselves as good swimmers Everyone wore a lifejacket. 25

26 Power Boaters: Also includes individual water craft Lower educated (73% are not college graduates) Older (44% over 30 years old) 79% visited this site the 10 or more days a year Seek nature, be with their family, and use their equipment, Profile: Middle age, local residents who boat frequently with their families. Three out of ten of us admit to having alcoholic beverages We rate ourselves as good swimmers, and Three quarters of us don t wear lifejackets. 26

27 Waders and Swimmers: Not well educated (71% didn t go to college) Young (71% under 29 years) 56% visited this site one time a year Seek nature, doing their own thing, and temporary escape, Profile: Local youth who go to the river once or twice to party and have fun. Three out of ten of us admit to consuming alcoholic beverages We rated ourselves as good swimmers (98%) We don t wear lifejackets either (98%). 27

28 Deceptiveness: How often do you visit the Potomac River? Can you tell when the river is dangerous? Do you consume alcohol while on the river? Do you wear a lifejacket? More analysis of these questions on the next slides. These following questions may suggest that people really don t know when the river is dangerous? Think about it Will I really be familiar with the river if I only visit it once or twice a year? 28

29 Infrequent Users: Overall, 46% recreate on Potomac two or less year Overall, 40% indicated that they visited this site only once a year 54% of tubers and 29% of waders & swimmers indicated that they will participate only once in this activity this year, 86% of canoeists and 48% of power boaters will participate 20+ times a year, Conclusion: tubers and waders & swimmer are infrequent users; canoeists and power boater are frequent users. I m a one time user. Of course, I can tell when the river is dangerous... can t I? 29

30 I Can Tell When the River is Dangerous: Overall, seven out of ten (69%) of Potomac River users agreed with the statement In other words, they believe that they know when the river is dangerous think flood & one time users Tubers were the exception, Unlike everyone else, over one half (57%) of our group were not sure that we could tell when the river was dangerous Maybe we can recognize our limitations? Conclusion: Potomac users think they know when the river is dangerous when, maybe, they really don t know. 30

31 I Wear a Lifejacket: Overall, four out of ten (42%) Potomac River users wear lifejackets Power boater are overstated since individual water crafts require lifejackets worn No tubers (98%) wore lifejackets Canoeists were the exception, Conclusion: At Harpers Ferry, canoeists do, tubers don t wear lifejackets. Either we are inherently safe or we wear lifejackets out of habit... Regardless, all (100%) of our group wore lifejackets. 31

32 I Consume Alcohol while on the River: Overall, one out of four (26%) of Potomac River users admitted to consuming alcohol while on the river Three out of ten (30%) of power boaters and wader/swimmers did too Canoeists didn t; tubers did, Conclusion: If you drink while on the river, do you really understand the dangers of the river? We are here to have fun. Four out of ten (40%) admitted to consuming alcohol while on the river. 32

33 The Dangers Are Deceptive: Most people are one time users who lack familiarity with the river and its dangers They practice unsafe practices... lifejackets alcohol consumption, Yet they think that they are safe, Conclusion: User behavior and attitudes are another reason why the non-flood Drowning Trap levels are deceptive and dangerous. If you visit the river once or twice a year and it is not at flood, should we really expect you to know when it is dangerous?. No, because you don t know enough to know when it is dangerous 33

34 Summary and Findings: As the depth of the river increases, its velocity and power to do something to you (drown) increases also Since you lack familiarity with the river, the benign looking river (non-flood) is deceptive because it doesn t look dangerous, Conclusion: It is the power of the river and the lack of user understanding which leads to the Drowning Trap. Depth of the River + Velocity + Deceptiveness = Drowning Trap 34

35 Where to Look for It: Spring flows in summer Summer weather during late Spring Dam releases Flash floods Anytime flows are higher than normal and the weather is warm. Depth of the River + Velocity + Deceptiveness = Drowning Trap 35

36 Quite simply, at the moderate Drowning Trap levels the river has the power to become a contributing factor in fatalities. The End 36