Forensic Hydrology

Forensic Hydrology

Article from:  The Forensic Engineering Report, Volume 12, No. 5

By Elvin Aycock, PE, RLS, ACTAR, PH, I-ENG-A Advisor

Forensic hydrologists study the causes and effects of water damage in legal cases, including flooding, erosion, drainage problems, and hydroplaning. This paper offers background on hydrology and forensic hydrology. It also provides examples of real-world situations where forensic hydrologists used their expertise to aid attorneys in legal cases.

Hydrology is the scientific study of water and its properties, distribution, and effects on the earth's surface, in the soil, and in the atmosphere.

The central theme of hydrology is that water moves throughout the Earth in a hydrologic cycle. The most vivid image of this is in the evaporation of water from the ocean, which forms clouds. These clouds drift over land and produce rain and snow. The rainwater flows into lakes, rivers, or aquifers, either evaporating to the atmosphere or eventually flowing to the ocean, completing a cycle.

Some of the water evaporates, some of it is intercepted by vegetation, and some of it travels over the land surface to streams. The streams flow into larger streams, which flow into rivers, finally flowing back to the ocean.

Water as a liquid or snow covers most of the surface of the Earth. By the process powered by gravity and the action of solar energy, an endless exchange of water, in vapor, liquid, and solid forms, takes place between the atmosphere, the oceans, and the earth’s surface. Water circulates in the air and in the oceans, as well as above and below ground.

The quantity of rainfall varies from region to region within the United States. At the same time of year, some regions are dry from lack of rain while other parts of the country experience flooding. It is not unusual for one part of the country to experience a hurricane, while another experiences a drought, and another has flooding.

Civil engineers and hydrologists study surface water—in particular, the measurement of its flow and volume. These studies are used to design the size of pipes for storm drainage systems and culverts. Other studies include designs for detention pond storage for development projects and water surface profiles of flood prone areas.

Local governments, for example, require hydrologic studies before the commencement of all significant building projects, and hydrology is applied when designating and managing flood plains. Hydrologists also are employed in the evaluation of water resources, wastewater systems, and irrigation projects. The public use of water for recreation and power generation also calls upon the work of hydrologists, who assist governments and private companies in controlling and managing water supplies.

Hydrologists use a variety of techniques. Some are simple and time-honored, while others involve the most cutting-edge modern technology, such as highly sophisticated computer models and satellite remote-sensing technology. Or, hydrologists may apply relatively uncomplicated methods for the measurement of snow depth or the flow of rivers and streams.

Hydrologists are particularly important in helping communities protect against flooding by identifying flood hazard areas and minimizing encroachment through the use of recommended state water buffers. By studying historical records, along with geologic maps and aerial photographs, hydrologists and engineers can make recommendations regarding the zoning laws for a particular area.

Forensic hydrologists investigate many issues, including the following: forensic hydroplaning

  • Flooding of property from heavy rain eventsHydroplaning on roadways caused by road defects
  • Development of land that prevents water from flowing in its natural watercourses
  • Erosion of the earth’s surface caused by the flow of surface water across unprotected soil created by land disturbing activities
  • Uncontrolled discharge of surface water, which causes flooding downstream

Forensic is a term that is associated with hydrology in legal matters. According to the Merriam-Webster Dictionary, “forensic” means “relating to or dealing with the application of scientific knowledge to legal problems.” In this sense, “forensic hydrology” typically refers to investigations of water issues and the need to identify the cause and damage incurred by storm water. The forensic hydrologist uses a number of hydrologic tools to determine the history of an event, such as computer modeling. He or she may need to determine when flooding began or upstream factors that have recently changed due to clearing of land for land disturbance projects.

Forensic hydrologic investigations commence with flow paths, both current and historic, and flow velocities. Changes in water flowing across the ground surface, drainage ditches, and drainage pipes often create adverse conditions downstream. The conversion of wooded land to impervious surfaces increases the quantity of storm water and the velocity of the water. The impervious area decreases the time of concentration of the water, which increases the peak flow. All of these effects can cause damage to downstream property owners.

In cases where surface hydrology has caused damage to downstream property owners, hydrologists examine historic aerial photographs to determine locations of land disturbance projects. The timeline of the downstream damage is compared with the timeline of the land disturbing activities.

For example, consider a site where soil erosion has filled in a downstream lake over a period of years. The aerial photographs help identify areas of land disturbance and the time frame for each disturbance. Where several developments have occurred over a period of years, the aerial photographs help the hydrologist identify the size of each Tire involved in hydroplaning development and the period of time the land was susceptible to erosion. The damages can be allocated to the developers based on the data gathered.

Without close oversight by the governmental agencies, developers may omit many of the erosion and sediment control measures shown on engineering plans. Because developers may have gotten away with this practice in the past, they may feel they can skip some of the erosion control measures to save money. This creates a situation where heavy thunderstorms—without appropriate control measures—can cause severe damage to downstream property owners.

A recent case that caused severe damage to the downstream property owner was caused when the developer tied a new storm drainage pipe into an existing pipe that was not adequately sized to handle the drainage from the new development. The property flooded, and the downstream landowners brought suit against the developer.

In another case, a contractor tied the discharge pipe from the detention pond into an existing storm drainage system. The existing pipe was only adequate for storms up to the 25-year storm event. The flooding problem developed because the developer did not clean out the siltation in the detention pond. Silt from erosion was allowed to accumulate in the detention pond, which decreased the volume of the storage for stormwater. When the storm event occurred, the water overflowed the emergency weir of the detention pond and flooded the downstream homeowner. The homeowner sued the developer.

Few developers understand how detention ponds function. Often, the grading contractor will not build the pond to the designed volume. This prevents the pond from being able to function as designed, and water overflows the spillway and floods the downstream residents.

Outlet structure control devices are often improperly sized or are not installed at the correct elevation. This creates a potential problem of more discharge through the outlet structure than the design model allows.

Forensic hydrologists are also called on to work hydroplaning cases. The flow of water across the pavement surface can be critical and dangerous to the motorist if the roadway surface is not constructed correctly. Often, this is a roadway defect created by improper construction methods used by the contractor.

The transition of the roadway from a tangent section to a highly elevated section can create an area of ponding. Unless viewed during or after rainfall, the area of ponding cannot be identified by the naked eye. A detailed elevation survey is needed to determine the area of ponding and the flow direction of water.

In one hydroplaning case, it was determined that the water on the roadway ran at an angle across the travel lanes onto the paved median. The water turned back and ran across the roadway again. This created a dangerous condition and caused a vehicle to hydroplane and crash into the median barrier. This section of roadway ran downgrade and entered into a highly elevated section. No inlets were provided to collect the water in the median, and as the grade increased to create the elevation, the water flowed from the paved median across the travel lanes. The depth of water on the roadway caused the vehicle to hydroplane.

The forensic hydrologist with an inquisitive mind and the use of sound engineering principles can help identify the cause that creates these types of problems. He or she can provide a valuable service to the attorney handling storm water drainage cases.  

The Role of the Engineer in Flood Damage Assessment

The Role Of The Engineer In Flood Damage Assessment

Article from:  The Forensic Engineering Report, Volume 18, No. 4

 

 


Damage assessment by an engineer following a flood event may be broken down into categories. First, there will be questions regarding the origin of the damage and second, engineers may need to evaluate the extent of damage and provide a scope of repair.

The source of the water must be determined; was it flood waters flowing from a creek, river or other water way, or was it ground water, sewer back up, sump pump failure, or a combination of sources. The source of the water will likely affect insurance coverage and should be clearly defined by the evaluating engineer.

Flood and water damage assessments may include evaluations of structural damage due to hydrostatic and hydrodynamic pressures. Structures may be lifted as a result of being buoyant in a flooded condition. Evaluation of foundations may need to be performed. Depending upon the forces of the floodwater, the weight of the building components and the connections to the foundation system, the structure may float from its foundation.

While the cause of the damage may seem obvious, conditions following a flood such as cracking in walls or ceilings, may not be related to the flood event. It is important to determine whether or not the damage existed prior to the flood event. Often damage that was present prior to a catastrophic event was unnoticed by the insured, who now believes the damage was the result of the event. The investigating engineer should be able to determine if the suspect damage was the result of a specific event.

Other services that may be required once the extent of the damage has been determined, include a scope of repairs to assist the claims adjuster in determining the value of the loss. Additionally, identification of construction or design deficiencies may be important factors to consider as they may have caused or contributed to the flood damage. All contributing parties must be identified as subrogation will be allocated to all parties who may have contributed to the loss. Moisture intrusion, microbial issues and air quality may also become issues or come into play. 

Assessing Wind Versus Surge Damage

Assessing Wind Versus Surge Damage, Reflecting On What Was Learned From Hurricane Katrina

Featured Article from:  The Forensic Engineering Report, Volume 18, Issue 4

 

A tremendous amount of information about the assessment of damage to structures in the determination of wind versus surge became available following Hurricane Katrina and the damages experienced there. Aerial photographs published by NOAA became of particular value as did topographical maps and aerial photographs taken prior to the hurricane. Utilizing these resources provided a means for engineers to supplement on-site observations.

Forensic meteorologists were also of particular value in providing opinions of the timing of events with regards to the wind versus surge components of hurricane damages. In many instances without this data, it would be impossible to determine the cause of damages. Professional engineers had a very daunting task to determine the forces that caused the destruction.

Structural engineers must understand the forces from surge water versus those of wind, including dynamic and hydrostatic conditions. The velocity of wind gusts and surge forces are taken into consideration.

Complete demolition of superstructures was consistent with powerful forces of storm surge, while structures located at higher elevations may be more prone to damage from greater wind forces.

The ethical pressures being faced by engineers in the determination of flood versus storm serge were also daunting insomuch that many property owners had no flood insurance. The determination of wind versus flood damages could bring financial ruin to individuals or families. Following the ASCE Code of Ethics provides some key factors to deal with these pressures such as honesty, integrity and objectivity.


The tremendous volume of buildings that needed to be inspected was also a problem. The Investigative Engineers Association put together guidelines for member professional engineering firms to provide catastrophe response in a organized fashion that would allow for a greater volume of investigations to happen in a more timely fashion. Time was an important factor to consider as there were over 250,000 people displaced by Hurricane Katrina and rebuilding efforts were not likely to start until insurance issues were resolved.


The Investigative Engineers Association organized a Catastrophe Response Committee consisting of professional engineers who were dealing with the situation in Louisiana and the gulf coast following the storm, to ascertain issues experienced and a way to deal with major catastrophic events such as this that may cause widespread damage in the future. The project included dealing with ways to organize a team of professional engineers and the distribution of assignments by area coordinates to eliminate as much windshield time as possible. Additionally the association put together the www.ienga.com website which enables its users, whom are all members of the I-ENG-A organization, to search for engineers by discipline, by state licensure and by availability. Technical training for CAT response including report formats, report timelines, safety, briefing, debriefing, structure of the CAT response team, the roles of Team Leaders, Investigative Engineers and Registered Professional Engineers, etc., were discussed as well as insurance requirements.


While the role of the I-ENG-A headquarters includes CAT response training and assistance with job processing, tracking, and data collection, the local member firm is to serve as the host or as the event management office. The models discussed teams of 3-4 engineers who would complete 6-8 assignments /day depending upon the complexity and travel time involved.


In conclusion, having engineers who are trained in these efforts with a plan in place before a catastrophe occurs can save a lot of time and money for all parties involved when a catastrophe does strike. If you would like to discuss catastrophe response with firms who may serve as your host, please feel free to contact association headquarters or visit www.ienga.net or www.ienga.com to locate the firm or firms near your areas of concern.

Sources: Forensic Engineering: Proceedings of the 4th Congress, October 6-9, 2006, Paul A. Bosela, Norbert J. Delatte, I-ENG-A CAT Committee