To make it easier to view the questions while you are out at the cache site, I am placing them on top. However, you will need to read the information provided in order to answer some of the questions. And, afterall, the purpose of an earthcache is to learn something.
Please provide answers to the following questions by sending me an email. Failure to do so or incorrect answers may, regrettably, result in your log being deleted.
- Onion Creek begins in Hays County and empties into what river?
- The creek has a normal full bank stage of about 15 feet, with flooding beginning at 17 feet. How many feet did the river rise at the given coordinates? (Clue: Calculate the difference between the elevation at creek edge and coordinates.)
- What is the name of the state park nearby that this park will someday be linked to?
- The Army Corp of Engineers began a 25-year floodplain buyout of all properties after the flood of 2001. Take a look at the residential properties surrounding this area. What does this tell you about where the worst flooding occured?
- Walk around this area and take a look at how Onion Creek curves through here. After reading the information below about how flooding occurs, based on past history of flooding in this area, should the existing homeowners feel secure? Why or why not?
What Is A Flood?
There is the potential for flooding anywhere and anytime it rains. A flood is a general and temporary condition where two or more acres of normally dry land or two or more properties are inundated by water or mudflow. And just because an area hasn't flooded before, doesn't mean it never will. Flood risk isn't just based on history, but on any number of factors and conditions. Although flooding can happen anywhere, certain areas are especially prone to serious flooding.
What Causes Flooding?
While there are many factors and conditions that can cause flooding, there are certain conditions that are more prevelant in Texas. Click here to view some interactive flood risk scenarios provided by the National Flood Insurance Program.
- Dams - Dams are an important resource in the United States, providing many functions, including recreation, flood control, irrigation, water supply and hydroelectric power. Dams range from massive concrete structures to more local earthen structures, such as those near a farm’s pond. Surprisingly, very few dams are owned by the federal government; in fact almost two-thirds are privately owned. While it is the dam owner’s sole responsibility for the safety and liability of the dam should something happen, the states have regulatory responsibility for about 90% of the 84,000 plus dams in the National Inventory of Dams.
- Flash Flooding - Flash floods are the #1 weather-related killer in the U.S. since they can roll boulders, tear out trees, and destroy buildings and bridges. A flash flood is a rapid flooding of low-lying areas in less than six hours, which is caused by intense rainfall from a thunderstorm or several thunderstorms. Flash floods can also occur from the collapse of a man-made structure or ice dam.
- Flood After Fire - Many areas in the western states are at an increased flood risk due to wildfires in recent years. After a wildfire, the charred ground where vegetation has burned away cannot easily absorb rainwater, increasing the risk of flooding and mudflows over a number of years. We've had our own share of wildfires here in Texas and properties directly affected by fires and those located below or downstream of burn areas are most at risk.
- Heavy Rains - Several areas of the country are at heightened risk for flooding due to heavy rains. This excessive amount of rainfall can happen throughout the year, putting properties and people at risk. Storms bring the heaviest rains to Texas between the months of November and April. Cresting rivers, backed-up storm drains or saturated ground can cause significant floods across the region during this time.
- La Niña - La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific (unlike its brother El Niño, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific). Each La Niña event is unique and can vary in strength, impact and duration. La Niña's can be quite strong and forecasters cannot predict how long they will last.
- Mudflows - Mudflows are rivers of liquid and flowing mud on the surface of normally dry land, often caused by a combination of brush loss and subsequent heavy rains. Mudflows can develop when water saturates the ground, such as from rapid snowmelt or heavy or long periods of rainfall, causing a thick liquid downhill flow of earth. Mudflows are different from other earth movements, such as landslides, slope failures, and even moving saturated soil masses in which masses of earth, rock, or debris move down a slope where there is not a flowing characteristic.
- New Development - Construction and development can change the natural drainage and create brand new flood risks. That's because new buildings, parking lots, and roads mean less land to absorb excess precipitation from heavy rains, hurricanes, and tropical storms.
- Hurricanes and Tropical Storms - Hurricanes and tropical storms can pack a powerful punch, with soaking rain, flying debris, high winds and tidal surges. In addition to causing extensive damage in coastal areas, they often bring flooding hundreds of miles inland with torrential rains and high winds, posing a threat to millions of people who don't even live on a shoreline. Eight of the ten most expensive Federally-declared disasters have been caused by hurricanes.
What Is A FloodPlain?
A floodplain, or flood plain, is a flat or nearly flat land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current. In other words, a floodplain is an area near a river or a stream which floods easily.
Flood plains are made by a meander eroding sideways as it travels downstream. When a river breaks its banks and floods, it leaves behind layers of rock and mud. These gradually build up to create the floor of the flood plain. Floodplains generally contain unconsolidated sediments, often extending below the bed of the stream. These are accumulations of sand, gravel, loam, silt, and/or clay, and are often important aquifers, the water drawn from them being pre-filtered compared to the water in the stream.
Geologically ancient floodplains are often represented in the landscape by fluvial terraces. These are old floodplains that remain relatively high above the present floodplain and indicate former courses of a stream.
The floodplain during its formation is marked by meandering or anastomotic streams, ox-bow lakes and bayous, marshes or stagnant pools, and is occasionally completely covered with water. When the drainage system has ceased to act or is entirely diverted for any reason, the floodplain may become a level area of great fertility, similar in appearance to the floor of an old lake. The floodplain differs, however, because it is not altogether flat. It has a gentle slope down-stream, and often, for a distance, from the side towards the center.
The Floodplains of Texas
Austin is in the middle of Central Texas flash flood alley, where there is a higher potential for high-magnitude flooding than in any other region of the United States.
Central Texas is in the path of weather from the Gulf of Mexico and the Pacific coast of Mexico, as well as cold fronts that blast in from the Arctic and clash with the moisture from the Gulf. The Balcones Escarpment that runs through Austin also intensifies the effects of these weather conditions.
When Austin has heavy rainstorms, creeks often flood. There also may be flooding in streets, buildings and yards not from creeks, causing local or localized floods. All flooding can be hazardous for people and property. The goals of Austins flood control programs are to promote flood safety and to reduce the impacts of flooding to protect, lives, property and the environment.
The Ever-changing Environment
Flood risk can, and does, change over time. Flood risks change for many reasons: new development, changes in levee classification, and environmental changes, to name a few. As a result maps are constantly being updated. These new flood maps, also, known as Digital Flood Insurance Rate Maps (DFIRMs), show flood risk at a property-by-property level. When new maps are issued, your risk for being in a flood prone area may have changed. The image below shows 12 watershed areas where Austin plans to rework the floodplain maps.
What Happened Here?
In November, 2001, an upper level low pressure disturbance stalled to our west sending waves of rain showers and thunderstorms northward over the Austin area. The heaviest rainfall fell during the mid and late afternoon hours of November 15, when 9 weak tornadoes also affected the area. Rainfall of 8 to 10 inches was reported over southern Travis and northern Hays Counties. Most low water crossings were flooded and dozens of water rescues occurred in the Austin Metropolitan area and in Travis County. More than 60 people were evacuated in this area, known as Yarrabee Bend, south and southeast of Austin where the flooding was as bad as it was back in October 1998. 50 injuries, 4 deaths, and over $500,000 in flood damage was reported in the Austin area. Onion Creek in this area had one of those fatalities when a 17 year old male drowned after he tried to walk through 3-4 feet deep moving flood waters after his car stalled in a low water crossing; he was washed off his feet and swept under his vehicle.
Since that time, the Army Corps of Engineers created a 25-year flood plain to buy out homes due to the high risk of flooding. Twice now, both in 1998 and 2001, this neighborhood had to be evacuated to prevent loss of lives. The ultimate goal was to remove all of the housing in this area and create a park.
The park is one of several parks in south east Austin that doesn't tend to get much attention. The trail here follows along the creek as it meanders its way towards McKinney Falls State Park, not far away on the other side of East William Cannon Drive. The trail starts at the waypoint "Trailhead". A short spur heads straight to the creek, but the main trail heads south paralleling the creek's path.
The trail here is less travelled and the path resembles a jeep trail cleared by periodic mowing. Since the trail is so close to the creek, the vegetation here is dense. During the month of August the summer grasses and brush can grow up to six feet tall, forming a wall of green on either side. Usually the mowed area is wide enough for a vehicle to say nothing of a hiker, though the plants can close in at a few spots. The trail surface is packed dirt, so things do get a little muddy after a good rain.
The most interesting thing about this area is what will be happening in the future. Plans are afoot to link this park with Springfield Park and into McKinney Falls State Park. The resulting trail system will be the most extensive in southeast Austin. Keep your eye on this area and consider helping out when trail restoration and building takes place. (Do I hear CITO?) It's good to know that what was once an area devastated by floods can be turned into something for everyone to enjoy. Just don't go there when it rains!!!
UPDATE: Yet another flood happened here on Halloween 2013. Below are a few facts from the City of Austin tweeter feed during that time:
- At peak during the flood, the flow of onion creek was twice the average flow of Niagara Falls.
- On 10/31/2013, one of the gages reported a rise of 11 feet between 6:15am and 6:30am. Many gages failed during the flood.
- 15 homes were destroyed, 259 were damaged.
A photo blog of the floods from the Austin American Statesman:
(visit link)
McKinney Falls State Park, down stream on Onion Creek was also severely affected:
(visit link)
Very sadly, 3 people lost their life in the Onion Creek/Bluff Spring neighborhood: Rev. Edward Jackson, 72, Josefine Rodriguez, 31 and her 8 month old baby Jay. Both Rev. Jackson and Mrs. Rodriguez were last seen alive in their vehicle trying to flee the floods.
Congratulations to JforceAtx for getting his first earthcache FTF and providing a link to Stevie!