Flooding From Excessive Rain Downstream From Earth Dams

The Daily Republic in South Dakota published an article that talks about an earthen dam that recently failed because of a nine-inch rainfall last 29th of July 2010. The heavy rainfall overwhelmed the dam’s capacity causing it to fail.

No injury was reported on the said event. The said damn was built in 1935, as were a number of them during the Work Programs after the Great Depression. In 2007, it was inspected by a Department of Game, Fish and Parks Engineer and he noted that they “were satisfied with the condition of the dam” during that time. It was then again inspected in 2008 and it was said 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 might just be living near one without you knowing it. A great percentage of these dams were built over 70 years ago and, in many cases, the owners today were not the same ones when they were initially built. For this reason, maintenance and inspection of these dams became less popular.

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.”

The South Fork dam, the country’s worst dam failure disaster in May of 1889, took over 2200 lives and almost half of which were under 20 years old. This incident happened in the town of Johnstown, PA, thus it was known as the “Johnstown Flood”. A 37-foot high wall of water hit Johnstown, located 9 miles downstream from the dam. It almost destroyed the entire city as 1600 homes and 280 businesses was flushed away.

In March 1928, the St. Francis Dam in California also failed. This caused a legislation to be enacted in and around the said state. 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. Because of the advance warning which enabled the evacuation of approximately 16,500, the casualties from dam failures has significantly decreased to 5 individuals

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, It should be noted 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.

Failure in The KaLoko Dam on the Island of Kauai, Hawaii in March 2006 has resulted to the death of 7 people. Two years after the said incident, developer James Pfluegar was indicated for manslaughter and reckless endangerment in relation to the dam failure. The incident had caused the country of Kauai and the State of Hawaii to pay out over $9 Million in 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 starts to travel outside of the control spillway. This causes 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 causes the remaining 20% of the U.S. dam failures. Piping is the internal erosion caused by seepage under and through the dam. This usually happens around structures such as pipes through the dam and spillways. Seepage can also be caused by animals, like beavers, muskrats, groundhogs, and other rodents, 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 flood, your best option is to avoid building in a flood zone, unless you elevate and reinforce your home. Have your area surveyed and investigated for dam failure and flood determination so you’ll know if your dream house is safe to be constructed in that certain area.

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. And among those, 636 are listed as high or significant hazard potential dams.

If you live downstream from one of these dams, find out who owns and 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.

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

What are FEMA flood maps?

flood mapsFEMA’s Flood Insurance Rate Maps (FIRMs) or just Flood Maps are provided after a flood risk assessment has been completed or updated for a community.  This study is known as a Flood Insurance Study.  The FIRM gives you 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

FEMA’s Digital Flood Maps

FEMA discontinued the production and distribution of paper flood maps in 2009 as part of its Digital Vision Initiative. This affected all the Flood Maps, boundary information, and study reports. However, clients can still view the products for free through their website or buy them in digital format.

To view these flood maps online, go to FEMA’s Map Service Center and key in your address (hi-lited area shown here) search for your home.  This will prompt you to then select the map that covers your area.  The Flood Maps are somewhat cumbersome to use online. It is best to go through the tutorial on the bottom right of the address search page for an easier and more effective use of the GIS map.

Estimate The Costs Of Flood Damage To Your Home

Why you need a flood survey before building a home?

The tool below allows you to calculate the costs of flooding. Select a home size that approximates yours and then slide the blue button up or down for the expected depth of flooding.

What can a flood survey do for you?

A flood survey can be done by your local land surveyor. This will help you in making important decisions such as buying a property and building your home. Through a flood survey, you get to save thousands of dollars worth of property. Also, you get to protect your family and achieve that peace of mind that everything you’ve worked hard for is safe.

The Basics of Land Surveying

What is Land Surveying?

Land Surveying dates back to ancient history. Surveying is used for multiple projects.  A survey is done to establish a specific location of a parcel of land along with its exact acreage.  It is used to ascertain boundaries for defining an area of ownership and tax liability.  It is also used to identify a piece of property by a written legal description or to provide a review of the accuracy of an existing description. Data from land surveying is of the utmost importance with regard to buying and selling land, and is also used to insure a clean and marketable title.

Other types of Land Surveying

There are many different kinds of surveys that can be performed. Boundary surveying is typically done for undeveloped land. This type of survey measures the actual physical extent of the property in question. Most surveys progress through the basic procedures regardless of the type being done. Any pertinent deeds, contracts, maps or other documents that contain a description of the property’s boundaries are located, studied and interpreted.

A determination is made of what the actual property description is deemed to be, along with the locations of any physical evidence of the boundaries. This can be in the form of both natural and man-made monuments or markers that exist in the field.

The property is then measured to establish the boundaries, not only using the appropriate existing monuments but with the creation and referencing of new markers where necessary. Measurements are accomplished using a total station and other land surveying tools. A total station measures both vertical and horizontal angles, as used in triangulation networks. After these steps are accomplished, the property description and plat are prepared.

Results of land surveying

Interpreting the results of a land survey is not as difficult as it may first seem. For instance, a property plat will usually contain a directional orientation which is typically indicated with an arrow pointing north. It will contain the bearing and distance of each boundary line, the property lines of other properties shown on the plat, and the names of adjacent property owners listed in the areas of their property.

Corner monuments, along with the names of any natural monuments (such as “Smith’s Creek”, for example) or a brief description of any unnamed natural monuments (such as the “30-inch pine tree”) are on the plat. There is also a title block containing the property’s location and name of owner, the surveyor’s name, the date the survey was performed, the scale of the plat and any other relevant data.

If you need the services of a surveyor for your land surveying needs, ALWAYS be sure that you’re hiring an experienced, certified, and highly competent professional surveyor. You can find out if the surveyor is licensed by visiting the Board of Licensure’s website.

Welcome to Dothan Land Surveying

Welcome to Dothan Land Surveying website

This site is intended to provide you with information on Land Surveying in the Dothan, AL and Houston County area of Alabama. If you’re looking for a Dothan Land Surveyor, you’ve come to the right site. If you’d rather talk to someone about your land surveying needs, please call our toll free number at (888) 936-8426 today. For more information, please continue to read.

dothan land surveyingLand Surveyors are professionals who measure and make precise measurements to determine the size and boundaries of a piece of real estate.  While this is a simplistic definition, boundary surveying is one of the most common types of surveying related to home and land owners. If you fall into the following categories, please click on the appropriate link for more information on that subject:

Dothan Land Surveying services:

    1. I need to know where my property corners or property lines are. (Boundary Survey)
    2. I have a loan closing or re-finance coming up on my home in a subdivision. (Lot Survey)
    3. I need a map of my property with contour lines to show elevation differences for my architect or engineer. (Topo Survey)
    4. I’ve just been told I’m in a flood zone or I ‘ve been told I need an elevation certificate in order to obtain flood insurance or prove I don’t need it. (Flood Survey)
    5. I’m purchasing a lot/house in a recorded subdivision. (Lot Survey – See Boundary Survey)
    6. I’m purchasing a larger tract of land, acreage, that hasn’t been subdivided in the past. (Boundary Survey)

 

Contact Dothan Land Surveying services Now.