Chapter 6 Weather & Water Conditions PDF

Chapter 6: Weather & Water Conditions Section 1 - Weather The weather at the beach is constantly changing and you need to be aware of these changes and the forecast for the day. Weather such as thunderstorms, wind, waves, fog, seiche, and even waterspouts all carry their own particular problems whic...

Chapter 6: Weather & Water Conditions Section 1 - Weather The weather at the beach is constantly changing and you need to be aware of these changes and the forecast for the day. Weather such as thunderstorms, wind, waves, fog, seiche, and even waterspouts all carry their own particular problems which lifeguards must deal with. Specific emergency action plans should be developed to deal with each type. Similarly, temperature and sun exposure are a continual problem for beachgoers. Lifeguards should be aware of the impact of the sun, its harmful rays, and how adverse temperature, both high and low, can affect the beach populace. There is a smart buoy located east of Wilmette (Buoy 45174) you can text it to receive real time data about weather including wind, water temperature, and air temperatures. This can be done by texting 45174 to 866-218-9973. 1.1 Sun Lifeguards are constantly exposed to sunlight and harmful UV rays. On all days be sure to wear sunscreen with minimum SPF 30 as it will reduce your chances of burning or developing sun-related skin cancer. Even on cool and cloudy days the sun still has a high degree of potency. It is important to drink plenty of water when exposed to the sun for long durations. In addition, be alert to the possibility of patrons on your beach suffering from either heat exhaustion or heat stroke. See the First Aid section (Section 7.5.3) of this manual for symptoms and how to treat such conditions. 1.2 Thunderstorms Thunderstorms are a common occurrence in Evanston in the summer, and lifeguards should be aware of the potential for them by knowing the daily forecast at the beginning of their shift. Immediately upon hearing thunder or seeing lightning at a beach or upon notification from the Beach Office, Beach Managers should note the time of thunder/lightning. They should remove patrons from the water and radio their supervisor immediately, start a 30 minute timer, and hang the no swimming sign. Supervisors should notify all other beaches to close. Staff should encourage patrons to leave the premises and staff should seek shelter in one of the beach offices or in the beach shacks. Bathrooms may also be used for shelter. After 30 minutes from the most recent thunder or lightning strike, the beach may reopen. There is a Thor Guard located at Dempster St Beach. The “Thor Guard” is a computerized system that can predict the probability of a lightning strike within 8-20 minutes before it will strike. The system is 97% accurate within a 2-mile radius. When there is a potential for a lightning strike within the coverage area, a strobe light will turn on and a warning horn will sound with an uninterrupted 15-second blast.The system operates 8 a.m. to 10 p.m. seven days per week mid-March to mid-November.  In the event of the Thor Guard being activated, the Beach Office will contact beaches via radio to notify them to evacuate the beaches and seek shelter. Once the Thor Guard has cleared, Beach Managers may reopen beaches. If beaches need to be closed due to seeing lightning, hearing thunder, or upon notification from the Beach Office, an announcement should be made over the megaphone to patrons. “Lightning has been detected in the area, the water is now closed. We recommend exiting the beach for your safety. The water will reopen after staff determine it is safe to do so.” 1.2a Lightning Lightning most frequently occurs within 10 miles of a thunderstorm Determine the distance of lightning from a location by using the "flash-to-bang rule” Begin counting at the sight of the lightning flash. Stop counting at the sound of related thunder. Divide the count by five (5) to determine the proximity in miles of the lightning strike (5 seconds = 1 mile; 50 seconds = 10 miles, etc.). Locations that offer protection from lightning: Fully-enclosed buildings that have grounded wiring and plumbing Fully-enclosed metal vehicles (no soft top convertibles) Locations that do not offer protection from lightning: Beaches Water Open-sided pavilions (such as picnic areas) Restrooms, changing facilities, and showers Lifeguard stands that are not fully enclosed and compliant with NFPA 780 lightning guidelines Tents or umbrellas Boats that are not designed or retrofitted to be compliant with NFPA 780 lightning guidelines Small personal watercraft (e.g. Jet Skis, kayaks, small sailboats) 1.3 Wind Strong winds can be the biggest weather-related threat on Lake Michigan. Wind direction is categorized by the direction it is coming from, for instance a wind blowing from North to South is called a North wind. Strong winds create large waves on Lake Michigan making swimming and boating conditions dangerous. For the Southwestern shore of Lake Michigan (where Evanston is located) waves can be created by strong North, South or East winds. With these waves come currents. When the wind blows “off-shore” it is coming from the West. “Off-shore” winds pose different dangers for boaters and swimmers. Non-motorized boaters can be blown away from shore and may be unable to return into the wind. Western winds can also blow the top-layer of water on the lake away from shore, which is then replaced by deep colder water, creating an “up-swelling” causing a drop in water temperature.  Other dangers the wind can pose is the potential threat of flying objects hitting an unsuspecting patron. Many times a beach umbrella will catch the wind and roll across the sand and can result in blunt force trauma. It is important for guards and staff to know the daily wind report in order to understand the potential dangers for the day. More information on waves and currents in Sections 4-7. 1.4 Seiches A seiche (sometimes deemed meteotsunami) is a standing wave in an enclosed or partially enclosed body of water. The term seiche comes from a word meaning “to sway back and forth.” If a storm system moves fast enough across the lake in an Easterly direction, it can pull water with it, enough to drop the water level of the Lake on the Western shore. Typically, the amount is very small, often too small to notice, however, on occasion the level can drop multiple feet. When a large seiche occurs and there is a rapid drop in water level, the water will then rapidly and dangerously rush back, often bringing more water than before. If you notice a large drop in water level, notify the beach office. 1.5 Waterspouts Waterspouts are basically tornadoes over water. Winds in excess of 40 mph are possible. The primary danger is flying debris, so shelter and protection should be sought if it appears that a waterspout may come ashore. Waterspouts may form during severe thunderstorm events, but waterspouts can also develop on relatively calm, partly cloudy summer days off the beach, over warm water. They can pose a direct threat to beachgoers, boats, and aircraft. They can sometimes come ashore and threaten beach patrons. The best way to avoid a waterspout is to move at a 90-degree angle to its apparent direction. Never move closer to investigate a waterspout. Some can be just as dangerous as tornadoes. Lifeguards should report sightings to fellow lifeguards and also to the local NWS office, so that appropriate warnings can be issued. 1.6 Fog Fog can severely limit visibility, to the point where you may not even be able to see the buoys bordering the swimming area. If this happens, the swimming area will be closed. Although not particularly dangerous, fog can play tricks on your eyes. Be aware of this and use your other senses (especially hearing) to alert you of potential problems. Fog can occur when a horizontal movement of warm moist air goes over a cold surface. Fog will happen more frequently in the morning and earlier in the summer season and typically goes away in the afternoon. 1.7 Temperature Air temperature can greatly fluctuate throughout the summer months on Lake Michigan. Be prepared for drastic changes in air temperature. During extreme heat be sure to drink plenty of fluids. On colder days wear appropriate clothing. Water temperature in Lake Michigan will get warmer throughout the summer. Temperatures can reach near 80 degrees Farenheit in the months of July and August. In the beginning of the summer season, however, lifeguards must be prepared for cold water. Cold water  removes heat from the body 25 times faster than cold air. The immediate effects of sudden immersion in water below 60˚F can be debilitating. In less than 30 seconds, it can cause uncontrollable rapid breathing and immediate constriction of blood vessels. After two to three minutes it can cause cold shock resulting in loss of reflex response. Prolonged exposure can lead to hypothermia (Section 7.5.3). Section 2 – Bathymetry and Structure Bathymetry is the underwater topography of the bottom of any body of water. The weather effects previously mentioned can change the layout of the sand under the water, however, the overall bathymetry of Lake Michigan remains fairly constant throughout any given summer. Every beach has unique physical attributes which can also present specific issues. Some beaches have physical structures or objects such as steep berms, rock outcroppings, drop offs and man-made structures such as breakwalls/breakwaters and piers. These things create their own unique physical hazards to swimmers. Typically, the area surrounding these objects/structures is prohibited to swimming and boating activity. 2.1 Sandbars Sandbars and troughs are found in areas where consistent lateral currents have cut a channel in the sandy bottom near the beach. The size, depth, and shape of these channels can vary greatly depending upon the type and consistency of the sand and the strength of the current. Sandbars may attract unsuspecting waders to the shallower area, but in order to get there, swimmers typically must traverse a section of deeper water which they might be unaware of. Swimmers, especially young children, who don’t pay attention can find themselves in water over their head or may fail to recognize a shallow depth change and upon diving head first into the water may hit their head on the bottom possibly causing severe cervical-spinal injuries. 2.2 Inshore Holes Inshore holes are depressions in the sand caused by erosion and are fairly localized. These areas can be extremely hazardous to small children who walk over them and “fall” underwater. Inshore holes can also be a serious hazard to lifeguards who can sprain or fracture an ankle or knee during a response to surf rescues. Inshore holes can also be caused by swimmers digging underwater. 2.3 Breakwalls/Breakwaters Breakwalls, or breakwaters, are large steel barriers that protect sand beaches from the effects of weather and longshore drift. They stand on the south end of every beach. Patrons are not allowed on or near them. Swimmers should never be in the water close to them due to the fact that the breakwalls create extremely strong unpredictable currents, deep holes, and are often surrounded by large submerged rocks. Onshore, children should be kept away from them as there tends to be rocks, glass, and other hazards along their base on the sand. 2.4 On Land Dangers The beach itself can pose some potentially dangerous conditions. At beaches around the world, there have been several fatal and near-fatal incidents caused by large holes in the  sand dug by beachgoers. In these cases, the victim fell into the hole and the hole subsequently caved in around them. This condition was only worsened by the would-be rescuers compressing the hole while standing next to the victim in an attempt to extract him/her. The sand can also hide glass, metal, rocks, and other objects that can cause injury. On very sunny hot days the sand can become extremely hot and cause burns on uncovered skin (especially on children’s feet). There are also several native animal species that may present a danger and in the wrong situation. Any cornered or threatened animal is a potentially dangerous one. Section 3 - Wave and Water Conditions Lake Michigan and the other four Great Lakes have ever changing water conditions, typically due to changes in weather, and conditions can change fast and are often substantial. In Evanston when we experience north, east or south winds, there will be an increase in wave action and dangerous currents can occur. Fresh water is less buoyant than salt water, thus is harder to swim in and more dangerous. During high waves, keep people as far away as possible from the breakwalls. On wavy days when swimming is allowed swimmers should be limited to an area directly in front of the main chair and close to shore. Once waves become too large and/or currents too strong, swimming areas will be closed. 3.1 Wave Formation Waves are normally formed by the force of wind on the water. Waves propagate when the wind grabs the water’s surface and pulls the water on top of other water. The distance wind blows over water is called fetch. The harder the wind blows and longer the fetch, the bigger these ripples get and the greater the transfer of energy, until proper waves are formed. Large waves can occasionally be created by strong local winds very nearshore, but most waves are formed by storms well offshore. Waves get their shape from the movement of this energy through the water. The water contained within the waves moves in circles underneath the passage of a wave. Water at the crest (top) of a wave will move forward, then as the trough (bottom) of the wave moves through the water will move backward. Even if the wind stops blowing, once waves are moving with energy, they can travel for long distances. Waves on the Great Lakes are much different from ocean waves. Ocean waves are typically “ground swell” or “swell” waves and are created by large storms out at sea and waves have traveled hundreds or thousands of miles before reaching shore. As these ground swell waves travel, they become smaller in height but longer and more spread apart from one another (the distance between waves is called period) becoming the large, rolling waves you see when on an ocean beach. Waves on the Great Lakes are typically wind waves created by wind directly that is still present as they are moving. Ground swell waves obviously start as wind waves, but due to the size of the ocean, the wind or storm that created them has typically died out before they reach shore. Wind waves, like those on Lake Michigan, have a shorter wave period, travel faster, and are more unorganized. Ocean waves usually have 7-12 second periods and Great Lake wave periods can be as short as 2 to 4 seconds. While swimming in Lake Michigan waves, waves will hit a swimmer every 2 to 4 seconds, leaving little time to recover or catch a breath and can quickly lead to exhaustion. The combination  of a short wave period with strong currents can quickly turn dangerous even for the strongest swimmers. 3.2 Wave Propagation Each wave contains a crest and a trough. They can be measured by: Wave Period — The time it takes two consecutive wave crests to pass a given point Wave Length — The horizontal distance between two wave crests (or troughs) Wave Height — The vertical distance between the crest and trough of a wave Wave Velocity — The speed at which the incoming set of waves advances 3.3 Breaking Waves As an open-water wave approaches the shoreline it becomes a shallow water wave. Wavelength decreases, wave height increases, and its velocity slows, but the period remains unchanged. As water depth lessens, the wave steepens, becoming higher and higher. Finally, upon reaching a depth approximately 1.3 times its height, the wave can no longer support itself and the crest falls forward, forming a breaking wave, which is commonly known as surf. Breaking waves cause an uprush of water, running up the slope of the beach. Once the uprush reaches its peak, gravity takes over and causes a backrush of water returning to the sea. Backrush, also known as runback or backwash, occurs wherever there is surf, but it is most powerful on steeply inclined beaches. Breaking waves can be classified into three primary forms: -Spilling Waves - are formed by swells as they move over flatter, wider beaches where the sea floor ascends gradually beneath them, with the crest of the wave spilling onto the wave face until the wave itself is engulfed by foam. -Plunging Waves - also known as shore break, formed when a swell suddenly strikes a steep beach, reef, or other obstacle and breaks with a flying spray, both expending most of its energy and transforming it into a spilling wave for its remaining distance to shore. -Surging Waves - are created where water is deep adjacent to shoreline cliffs, reef, or steep beaches, with the waves keeping their rounded form until they crash against the shoreline barrier with very strong uprush and backwash. 3.4 Wave Hazards Waves cause problems for beach visitors because of their tremendous power and energy. Wave energy is proportional to the square of the wave height, so small increases in wave height signal disproportionately greater increases in wave energy. (Basically bigger waves are much stronger than smaller waves)  Breaking waves can violently thrust swimmers and surfers to the bottom, causing serious trauma to the head, neck, back, and other parts of the body. They can throw people into rocks or other fixed structures. Uprush and backrush may knock visitors down and injure them, or pull them into deep water. When surf is rough, backrush may be met by a second, forceful uprush, creating violent turbulence that is dangerous to the young and old, especially those who lack the strength to maintain their footing when caught up in this force. Lifeguards typically enter the wavy water using “dolphin dives.” Dolphin dives are done by running and diving toward the middle of an incoming wave just before it breaks and swimming out on the seaward side. Returning to a beach with shore break requires timing and speed to get safely ashore before being hit by the next incoming wave. Section 4 - Currents When waves break in shallow water, the structure of the waves breaks down and the white water that you see associated with breaking waves physically moves towards the shore on the surface. The water level rises due to the addition of incoming water. It is this wave breaking and moving water that ultimately creates strong currents in the surf zone and along the shoreline. Because underlying topography is typically irregular, wave breaking is uneven along the beach. Any bodies of water where breaking waves of significant size are present, whether the ocean or a large lake, may experience these currents. 4.1 Longshore Current Longshore currents are also known as lateral currents or lateral drifts. This is the large, prevailing current in Lake Michigan. All other currents are essentially offshoots of the Longshore Current. Lake Michigan’s longshore current basically creates a large counter-clockwise circle around the Lake, so here in Evanston the current runs from North to South. When there are Northerly winds and waves, the current becomes much stronger. The stronger the Longshore Current, the stronger the other currents can be. As the name suggests, longshore currents move parallel to, or the ‘long’ way along the shoreline. These currents are created when waves come from an angle and push water along the beach as the waves break. These currents may be so strong that a swimmer is unable to retain their position relative to shore. Those who do not pay attention can be swept sideways into a structural or rip current and then beyond the breakers or immovable objects such as promontory points, jetties, groins or piers. 4.2 Structural Currents While it can be difficult to predict when and where most currents will occur, the opposite is true for structural currents. The currents found alongside or as a result of structures like piers and breakwalls — called structural currents — are usually always present but can increase  when the waves are high. Structural currents are dangerous on their own, but when paired with others like longshore or rip currents, the combination can create a washing machine effect or move the swimmer from one dangerous current area to another with no clear path to safety. Assume there are always Structural Currents along the North edge of our breakwalls moving out into the Lake, on North wind/wave days, these currents will become exaggerated, easily pulling swimmers out beyond the breakwall and into the Lake. 4.3 Rip Currents Rip currents occur when waves spill over sandbars and water volume piles up in a trough between the sandbar and shore. Water over-accumulates in this trough and with nowhere else to go, eventually breaks a hole in the sandbar, causing a sudden surge and rush of water back out into the lake. Based upon USLA National Statistics, rip currents account for more than 80% of all surf beach rescues. Statistically, spring and early summer are the most hazardous times of year because of the unstable condition of the bottom created by winter storms and ice. These conditions are further aggravated by colder water temperatures which affect both swimmers and lifeguards alike. To escape a rip current, swim on an angle towards the shore perpendicular to the current. If you are unable to swim out of the current go with it until you are in calmer waters, then try again. If you are near the breakwall, wait to swim out of the current just after you have reached the end of it, the current will be weaker here. Rip-Currents that are created in part due to sand-bars that can pop up instantaneously (flash rips) widen or move during the course of the day (transient rips and traveling rips) or be determined by a fixed object (structural rip). While somewhat common in Michigan and Indiana, where there are sand beaches that go uninterrupted by structures in the water for long distances, rip currents are not extremely common in Evanston. Because of our breakwalls, piers, changing rocklines, and other structural objects that break up our shoreline, Evanston does not have an expanse of beach long enough to create rip currents on a frequent basis. Lifeguards however, should still be aware of how they are caused and how to spot them, as they can still occur. The most prevalent clues of a potential rip include: rough or choppy waves; waves that seem to be going the wrong direction or are shaped differently from the rest of the visible waves; a difference in color of the sand or detritus in the water; objects on the surface floating against the direction of the waves or wind; patrons moving in a different direction than the one they seem to be trying to move in; a calm and flat area surrounded by a wavy area. 4.4 Outlet Current Outlet currents can be found where rivers and streams empty into the Great Lakes. The flow of water from the river or stream can move quickly. As it enters the open water of a lake, it  may take a while for that current to dissipate. Pair that with currents that are present in the lake and the situation can become dangerous. 4.5 Channel Current A channel current is like a river running parallel to shore. With a channel current, typically there is an island or structure such as a large group of rocks not far from shore. A channel current forms when the flow of water speeds up as it goes between the island and shore, like a bottleneck. This is made worse by the presence of a submerged or partially submerged sandbar connecting the beach to the island, which allows pressure to build behind the water and waves until it breaks through. When the wind speed increases, the waves also increase in intensity, and this causes the current to become stronger and faster.