Down on the Bayou (Part 3)
As discussed in our previous column, for both commercial and residential development the City of Houston currently regulates minimum flood protection elevation of 0.2 percent flood elevation plus 2 feet. Harris County currently regulates minimum finished floor elevations to 0.2 percent flood elevation in areas where the drainage infrastructure meets the current design standards, and 0.2 percent flood elevation plus 2 feet in non-conforming subdivisions. Since elevation is a passive system, and requires no significant maintenance or manual intervention, elevation is generally the first option selected by engineers and architects for commercial systems. It is important to understand that commercial properties, unlike residential properties, have the additional option of floodproofing buildings to the same elevations as previously noted.
The Methodist Hospital in the Houston Medical Center provides us with a good example of utilizing floodproofing techniques in concert upon an existing commercial development that would be at a minimum, difficult to elevate. A combination of passive concrete walls and flood activated dams at parking entrances stand vigilant and unnoticed unless activated by a flood event. Upon activation these preemptive measures create a berm protecting the region’s critical infrastructure from Houston’s mass flood events. For additional protection of its subsurface improvements during major storm events, Methodist has implemented a system of flood doors between their underground parking facilities and the main hospital. Originally, flood doors were modeled after doors in submarines. They were heavy and required a sailor to close and dog the hatch. This technology has advanced significantly in the last few decades and can now be remotely activated, as is the case with Methodist. These more advanced systems should be inspected regularly to ensure that the electrical and mechanical components correctly close the doors.
Flood activated dams, another option, are activated when rising surface water causes the dam to automatically close during flooding events. They have components that are below ground in most cases, and rise out of the ground during flooding events. A less expensive option is a flood door which covers only part of the doorway, and is called a flood barrier shield. These systems are reasonable to implement on existing commercial properties that have been remapped into the floodplain during a recent map update. They do require storage when they are not in use, however the system can be designed to store the shields below ground at the doorway they are protecting, or above the doorway they are protecting for easy activation during a storm event. Additional methods which can provide some limited, however unpermitted, protection include sand bags, inflatable barriers, or water filled bladders.In contrast, less shaded map areas that have between a 1% chance and 0.2% chance of occurring in any one year still have between a 26% chance and 6% chance of flooding over a 30-year mortgage period. FEMA does not require insurance in this area, but it may be wise to purchase. The odds of a house fire (0.25%) and the odds of a 0.2% flood event in a less shaded area are very similar, and almost all homes have fire insurance.
As many of you are aware, HCFCD is in the process of updating flood maps for all of Harris County. In my next article I will be discussing some of the opportunities available for a landowner to capitalize upon during the period between FEMA issuing maps for comment and FEMA formally adopting those maps.
Dr. Culp is the most senior hydrologist at Tetra Land Services and has three decades of civil engineering experience. His Ph.D. scholarship studied the effectiveness of structural BMP for the control of storm water pollution in Harris County while performing water quality monitoring and modeling upon selected ponds for the county. Dr. Culp also co-authored the City of Houston stormwater quality management plan. He is one of Texas’s original Certified Floodplain Managers. Recently, Dr. Culp and his staff have developed a series of drainage studies for Industrial and Oil Majors along the Texas Gulf Coast. Dr. Culp is married with two children, and lives on his farm in Southwest Houston.