Embankment, Abutment, and Foundation Seepage


“All Dams Leak” is a common and true phrase. But what makes seepage (or leakage) a potential to cause damage. Basically velocity and pressure. There has to be sufficient pressure (head) that generates a velocity in the voids of the soils that will erode particles. The basic equation for velocity (k) is: v = ki

where; k = permeability (ft/day), i = gradient = delta h / L, h = head (ft), L = seepage path length (ft).

Erodibility of soils is mainly based on particle or grain size (coarse vs fine sands) and cohesion (non-plastic silts vs clays).

Earth Embankment with Left Side Spillway

Seepage and Flownets

Seepage pressures and gradients must be analyzed for all types of dams and foundations using flownets. In order to fully understand the seepage pressures and velocities at a dam, graphical flownets must be developed and verified with field observations when appropriate. Foundations that are analyzed based on seepage through broad geologc units, will most of the time miss important details within the units that may present seepage problems at the dam project.

Seepage Control

Seepage berms are extremely beneficial when added to a seepage collection system, some of those are:

-increased drainage

-reduction in uplift pressures

-increased resistance to sliding

-increases in effective stresses and available shear strength

Drainage capacity of a gravel section can be determined by the procedure outlined in SD&FN (Cedergren 1989).

for the filter aggregate kh = 10 ft / day [1], for the coarse gravel aggregate kh = 100,000 ft / day. The area is approx. = 3 sq ft. The slope of the pipe and the hydraulic gradient in the gravel section are equal to 0.01. Using Darcy’s law . Q = 22,000 gallons per day (gpd) or 15 gallons per minute (gpm).

with a 6″-dia drainage pipe, approx. Q = 260,000 gpd or 180 gpm. Using 0.1 as the gradient, the Q or flow volume values of course are 10 times larger.

Dam Cores

What’s the purpose of the “core of a dam?” Basically it’s economics. By reducing the reservoir hydraulic gradient in a shorter distance than more pervious materials, adding a core allows the use of steeper slopes for zones of materials downstream of the core, thus reducing the volume required to build the dam. Technically speaking, adding a core increases the effective stresses of the embankment and foundation materials downstream of the core. Higher effective stresses allow for greater available shear strength. Dams that are built with cores of higher permeability require flatter downstream slopes.

Heavy Equipment Icons


What are some iconic types of Heavy Equipment in the industry?


D10 Dozer – Operating Weight: 154,700 lbs (Caterpillar)

772 Off Highway Truck (Caterpillar)

Gross Operating Weight: 181,000 lbs, Payload: 50 tons, Heaped: 41 cu. yd.


992 Wheel Loader – Bucket Capacity: 14 to 16 cu. yd. (Caterpillar)

Construction Equipment | Construction Industry Product Information

Design Earthquakes – Definitions

For Concrete Structures: OBE (operational basis earthquake) = 144-yr Return Period (50 percent chance of being exceeded in 100 years).

Max. Design EQ: for Structures Defined As Critical use MCE, In general for other structures, MDE = 950-yr return period (10 percent chance of being exceeded in 100 years).

MCE is defined as the greatest earthquake that can reasonable be expected to be generated by a specific source (which comes from a deterministic site hazard analysis).

USACE references: Stability Analysis of Concrete StructuresEarthquake Design and Evaluation of Concrete Hydraulic StructuresEarthquake Design and Evaluation for CW ProjectsSafety of Dams – Policies and Procedures.

Dam Failures in March – St. Francis Dam Disaster


St Francis Dam Failure, 12 March 1928.  Failed catastrophically upon its first full filling, near midnight, killing at least 450 people.  Seepage (dirty water)  was observed the day of the failure. A massive landslide occurred in the dams left abutment, comprised of schist.

“Greatest American civil engineering failure in the 20th century.”

Remaining Portions of Dam After Failure.

Historical Society of Southern California:  St. Francis Dam Disaster.

Excellent Photo Display at:  St. Francis Dam collapse – Framework – Photos and Video – Visual Storytelling from the Los Angeles Times.

Type: Concrete Gravity Thick Arch Dam, Maximum Height = 195 feet, Storage (at time of failure) = 38,000 acre-feet

Dam Failures in February

PLEASE Add to the Blog of Dam Disasters that Occurred in February (any year).  Join the community of knowledge and contribute.  Enter Your Own Personal Observations. Share pictures you might have of the site during the incident.  It’s Valuable Information for Everyone. Thank You.

LOWER SAN FERNANDO DAM FAILURE, 9 FEBRUARY 1971, LOS ANGELES, CA.  Due to Liquefaction and the Magnitude 6.7 San Fernando Earthquake of 1971.


The Los Angeles Dam Story.


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Dam Failures in January

Please Add to the blog of Dam Disasters that occurred in January.

“Lower Otay Dam Disaster – United States (1916) – Death Toll: 40


The Lower Otay Dam constructed on Otay River is situated in San Diego County, California, United States. Its purpose was to serve as a large water reservoir.

In January 1916, after a heavy rain spell hit on the southern region of California, the dam topped up and started releasing water. Unfortunately no proper rescue measures were taken and the reservoir emptied causing great damage in the nearby areas.”

via Top 15 Worst Dam Disasters Ever.

The dam failed at the right abutment on 27 January 1916.  It was a earth and rock fill dam with a steel core.

“Lower Otay Lake and Dam is a rock fill structure with a massive masonry pour as a base for the steel plates. The steel plates, riveted together, acted as a diaphragm to control seepage and can be seen at the middle of the dam. A pyramid formed by the steel members during construction was used as a crane to move rock, steel and concrete to their proper location in the structure. Explosives were used to break rock into smaller units for use in the dam. As an example of the effect of blasting, records show that 100,000 pounds of powder loosened 150,000 tons of rock.”