Flooding From Excessive Rain Downstream From Earth Dams

rose hill dam failure - floodingAn article from the Daily Republic in South Dakota talks about an earthen dam that recently failed there due to a 9-inch rainfall event on July 29th of this year.

This rainfall event “overwhelmed its capacity” causing the failure of the earth dam.  There was no report of injury downstream of the dam. This dam was built in 1935, as were a number of them during the Work Programs after the Great Depression.

A Department of Game, Fish and Parks Engineer said that they “were satisfied with the condition of the dam” during inspections in 2007 and again in 2008 and that the dam breach “was caused by an extraordinary natural event and not by any structural weakness in the dam.” (Photograph by Laura Wehde/The Daily Republic)

Earth dams are almost too numerous to count around the country. In fact, you probably live a lot closer to one than you might think. A large number of dams were built over 70 years ago and, in many cases, the owners of the dams are different than when they were built. This makes maintenance and inspection of the dams less regular.

FEMA estimates “there are over 80,000 dams in the United States”, and that approximately “one third of these pose a ‘high’ or ‘significant’ hazard to life and property if failure occurs.”

In the countries worst dam failure disaster, the South Fork dam failure in May of 1889 killed over 2200 people (almost half of which were under 20 years old) in the town of  Johnstown, PA.

This is known as the “Johnstown Flood.”  A 37-foot high wall of water hit Johnstown, located 9 miles downstream from the dam. The entire city was almost destroyed, including 1600 homes and 280 businesses.

After the failure of the St. Francis Dam in California in March 1928, legislation was enacted in and around California. This, and other later legislation led to life-saving advance warning when the Baldwin Hills dam near Los Angeles, California failed on December 14, 1963.

Only 5 individuals were killed because of the advance warning which enabled the evacuation of approximately 16,500.

Even though there have been far less loss of lives in the United States from dam failures since the 1970’s, reports that…

there were 132 dam failures and 434 “incidents” between January 2005 and January 2009.

Of course, I should note that the failure of the earthen levees near New Orleans, LA during and after Hurricane Katrina are purported to be responsible for killing more than 1000 people.

The KaLoko Dam on the Island of Kauai, Hawaii failed in March of 2006 killing 7 people. In November of 2008, the developer, James Pflueger, was indicted for manslaughter and reckless endangerment in relation to the dam failure. The county of Kauai and the State of Hawaii paid out over $9 Million in settlement of lawsuits after the failure.

Cause of Dam Failures

Heavy rains cause overtopping, which is by far the most common cause of dam failures. Dam spillways and structures are typically not designed for more than a 1-percent chance (aka 100-year) storm event.

When a rain event exceeds this, the water begins to travel outside of the control spillway. This leads to erosion of the soil on the dam from the excessive amount of water traveling over it.

It is also possible for overtopping to occur from smaller rain events because of debris blockage of the outlet structure or spillways or because of settlement of the dam crest.

Foundation defects, including settlement and slope instability, cause about 30% of all dam failures.

Seepage or Piping is the cause of another 20% of U.S. dam failures. Piping is the internal erosion caused by seepage under and through the dam. It often occurs around structures such as pipes through the dam and spillways.

Seepage can also be caused by animals burrowing in the dam, by roots of trees growing on the dam, and through cracks in the dam.  All earth dams have seepage resulting from water permeating slowly through the dam and its foundation.

But this seepage must be controlled or it will progressively erode soil from the embankment or its foundation, resulting in rapid failure of the dam.

What Should You Do To Protect Home?

Since the failure of a dam causes excessive flooding, one of the best courses of action is to avoid building in a flood zone, unless you elevate and reinforce your home. You should have your area investigated for flood determination or dam failure.

Do you live downstream from a dam? Is the dam a high-hazard or significant-hazard potential dam?

To find out, contact your state or county emergency management agency and/or visit the National Inventory of Dams. There are around 2,228 dams on the National Inventory in Alabama. Of those, 636 are listed as high or significant hazard potential dams.

If you live downstream from one of these dams, find out who owns the dam and who regulates the dam. This information should also be available from the National Inventory of Dams.

Next, find out if there is an Emergency Action Plan in place. Again, consult your state or county emergency management agency. (Alabama Emergency Management Agency)

Strangely enough, Alabama is the only state in the United States that has not passed dam safety legislation.

If you want help with investigating a piece of property you are considering purchasing or of one you already purchased, please call Daphne Land Surveying today at (251) 270-4140 or better yet send us a contact form request.

How To Find Your Home On FEMA’s Flood Insurance Rate Maps

FEMA’s Flood Insurance Rate Maps (FIRMs) are issued after a flood risk assessment has been completed or updated for a community.  This study is known as a Flood Insurance Study.  The FIRM shows the Base Flood Elevations (BFEs) and insurance risk zones in addition to floodplain boundaries.  The FIRM may also show a delineation of the regulatory floodway.

Once the “insurance risk zone”  (commonly referred to as the flood zone) is determined, actuarial rates, based on these risk zones, are then applied for newly constructed, substantially approved, and substantially damaged buildings.  FEMA uses these rates to determine the insurance rate you will pay for flood insurance.

To view these maps online, go to FEMA’s Map Service Center and enter your address (hi-lited area shown here) search for your home.  This will allow you to then select the map that covers your area.  The Flood Maps are somewhat cumbersome to use online. I suggest going through the tutorial on the bottom right of the address search page in order to learn how to maneuver around in this GIS map.

If you are located in the City of Daphne, you might also check out the Daphne Interactive GIS maps for more information and a little easier interface. Check the FEMA Flood Insurance Rate Map box on the left to view the flood zones on this map.

Call Daphne Land Surveying at (251) 270-4140 or better yet send us a contact form request if you need help with this process or if you discover you are near a flood zone and need an elevation survey completed.  We are here to help you minimize your flooding risk.

Land Surveying and GPS

Land surveying is a profession that greatly utilize the GPS system.

land surveyingToday, man-made constellations are in orbit. Their purpose is to provide instant, exact and global positioning information. This global positioning system of GPS is revolutionizing the modern construction sites, automating and guiding land surveying equipment, providing instantaneous circles and volume gap, simplifying total and controlled surveys. Nearly everyone involved in the land surveying and construction industry has heard something about satellite positioning technology or maybe you or someone you know is already using it. Whether an operator or a casual observer, there are still many questions about how this exciting system really works.

These positioning satellites don't stay in one place like the stars; they orbit the earth about twice a day. Constantly transmitting uniquely identified radio signals that can be perceived by specialized units on earth. These signals are used to precisely measure the distance to the receiving instrument from each satellite visibly overhead.

Just as stars have exact locations in the sky, the locations of the GPS satellites are also defined, becoming orbiting reference points. Using a process based on triangulation, a GPS receiver processes the signals from multiple satellites to compute an accurate position on Earth, which is why it is widely use in land surveying.

For mobile applications that require high accuracy, such as three dimensional machine control, there are two requirements that must be met. First, the signals from a minimum of five satellites must be received at all times. And second, those five satellites must be distributed across the sky. This is called Dilution of Precision or DOP. The simple rule of thumb is this, the more satellites received the better your system will perform.

land surveyingAll land surveying receivers incorporate standard GPS tracking technology; unfortunately the GPS satellite constellation alone cannot continuously make the minimum requirement of accurate mobile positioning. For any given location, there are times in a day when there are less than five available satellites or very poor DOP.

Now, consider a land surveying job site with trees, buildings, or other obstructions when satellite receptions are easily be further reduced. All land surveying GPS receivers suffer this same problem because they all use the same satellites to operate.

Even the planned signal modernization to the GPS satellites won't solve this problem. An obstruction that blocks one signal blocks all signals from that satellite. A land surveying equipment provider has solved this problem. The solution isn't adding more signals from the same satellites; it's adding more satellites.

Today, there is a second positioning satellite constellation in operation, the Glonass System. This positioning system is operated and maintained by the Russian government; much like the GPS is operated and maintained by the United States government; combining these two satellite constellations give land surveyors access to 38 different satellites; 14 more than a GPS-only system.

The additional satellites mean stronger and more accurate positions and better performance in obstructed land surveying areas. These additional satellites mean maximum up time in all land surveying locations, in all conditions.

For an up to date and accurate land surveying service, contact Daphne Land Surveying at (251) 281 – 2081 or better yet, you may fill out our contact form request and a licensed land surveyor will contact you. 

Licensed Land Surveyor: Using GPS to Track You – Is It Real?

A licensed land surveyor trusts his GPS system like  his gun in a battlefield. Though it sometimes do not provide all the info that you may need, it is nonetheless very helpful in producing an accurate boundary survey.

Many have heard of “Big Brother” being able to track our movements. One of my favorite TV shows is “Person of Interest” where a secret machine keeps track of all conversations and people’s “criminal intent” in order to help the heroes stop the crimes before they happen.

While I’m SURE that there are tracking capabilities in most cell phones and different government agencies CAN track our locations, we might be a ways away them being able to determine criminal intent.  But there IS a recent application in England that I found very interesting.

licensed land surveyorNestle (yes, the chocolate company) is placing GPS Trackers in six KIT KAT bars in their aptly named “We’ll Find You” marketing campaign in the UK. When the person opens the package it notifies KIT KAT and the prize delivery team will find them within 24 hours and present them with a check for £10,000 (about $16,000.) See the article here.

Just about all new type cell phones, all smart phones, iPads and other tablets, lots of cars (more than you think), public transportation vehicles, golf carts, and watches have GPS devices in them now days. Another place they are, and rightly so, are in ankle monitors used by law enforcement. But, what you might not realize is that the electronic devices mentioned above can work just like the ankle monitor. Now, while it is true that you can disable the GPS tracking device in your cell phone or tablet, that doesn’t give all of us complete comfort in walking around with these devices on us.

Now, I’m not trying to be a conspiracy wonk here, but it is POSSIBLE that this could be taken advantage of by well-meaning agencies. And, as we know, law enforcement can make mistakes in identifying the correct suspect.  Of course, as a licensed land surveyor myself, I WANT emergency services to be able to find me if and when I need their service, so this is a double edged sword. Most of us probably have nothing to worry about in this regard, but if you worry about this sort of thing, it could keep you up at night.

licensed land surveyorEven as a licensed land surveyor, having used GPS technology in land surveying for almost 20 years, I still trust them more than I should.

One example is when I was in an unfamiliar town my GPS navigation device told me to take a “road” to the right. I slowed down and attempted to turn but it was a power line.  Not wanting to believe that Gizell was wrong (yes I named her), I went to the next street and turned and tried to find the “road” further back. I ended up driving down the sandy power line, which turned into a bike lane until I was finally stopped by a gate. As I backed down the bike lane looking for a turn-around spot I thought, “maybe this wasn’t a road and maybe my GPS device is fallible.” Of course, I soon justified Gizell by recalling that a human had to “digitize” the roads in and she just did what they programmed her to do.

If you need to turn off your GPS tracking device in order to sleep tonight, call your device’s customer service line and stay away from KIT KAT bars. If you would like to find out how GPS surveying technology can help you in surveying your property boundary, call a Licensed Land Surveyor at Daphne Land Surveying at (251) 270-4140.

Land Surveyor: Famous Land Disputes All Over the World

land surveyorA land surveyor may not be recognized as much as a doctor or a lawyer, but no one can dispute that they play a very crucial role on Earth. As proof, several countries all over the world have unsettled land disputes over other countries. Some may have been settled through the International Court of Justice, Treaty conditions, or a claimant country’s sovereignty has been recognized. And of course, these were all settled with the help of a land surveyor.

Let’s take a look at some of the famous land disputes all over the world settle by a land surveyor:

  • Mayotte (Africa) – Claimants are France and Comoros. France gained full control under the 2009 referendum, the population supported becoming an overseas department of France, and so became one on March 31, 2011.
  • Ligitan and Sipadan (Asia) – Claimants are Malaysia and Indonesia. The 2002 International Court of Justice ruling awarded both islands to Malaysia, but left unsettled the maritime boundary immediately southwest and west of the islands between Malaysia and Indonesia.
  • Eastern coast of Narva and Petseri County (Europe) – Claimants are Russia and Estonia.Russia recognized them as a part of Estonia with Treaty of Tartu, 1920. After the fall of the Soviet Union, Russia continued administering it.
  • Tuzla Island and Strait of Kerch; Sarych (Europe) – Claimants are Ukraine and Russia. The conflict arose in 2003 when the Russian authorities started to build a dam towards the island. Since then Ukraine established a border garrison on the island for a closer surveillance. The reason for the conflict is the fact that Tuzla island strategic location gives Ukraine full rights over the main channel in the Strait of Kerch and, thus, the access to the Sea of Azov.
  • San Andrés and Providencia (Central America/Caribbean) – Claimants are Colombia and Nicaragua. Colombia currently has full control because Honduras de facto recognises Colombian claim.
  • Los Monjes Archipelago (South America) – Claimants are Venezuela and Colombia. Velenzuela gains full control because Colombia no longer claims the islands, only the surrounding waters.

A piece of parcel is something that signifies power and resources thus many countries fight over it. If big countries have unsettled disputes over a piece of land, small land disputes also happen between siblings, husband and wife, and neighbors. Though you can’t hire a land surveyor from an International Court to settle your small land disputes, you can always hire a local land surveyor who can survey your property and resolve any encroachment claims and/or equally divide a property as mandated by law.

A land surveyor plays a very vital role in settling land disputes, big or small. If you are in a situation that you may need the expertise of a land surveyor, please contact Daphne Land Surveying at             (251) 270-4140        today or go to our Contact page and send us an email.