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Flood Plain Information for Homeowners

Although almost any part of Baltimore County can flood, there are some areas more likely to do so than others. These areas are called flood plains. Baltimore County flood plains fall into two main categories, tidal and riverine:

  • Tidal flood plains are areas influenced by the astronomical tides such as the Chesapeake Bay and the tidal rivers adjacent to it. Tidal flooding results primarily from wind and waves and although dangerous, their effect is limited to areas below certain elevations.
  • Riverine, or non-tidal, flood plains are those areas inundated by streams fed by rainfall and which flow downstream by gravity. Such flood plains can be even more dangerous than tidal since water flowing under gravity can build up considerable energy on its way downstream and can easily wash away buildings, vehicles and people. Little creeks and brooks flowing just a few feet wide and shallow enough to wade across during dry weather may become raging rivers many feet deep and hundreds of feet wide in a flood event.

Fortunately there are resources available to identify flood-prone areas so no one needs to be caught by surprise.

Federal Flood Insurance Rate Maps

The worst of the flood plains are mapped on the Federal Flood Insurance Rate Maps (FIRMs) published by the Federal Emergency Management Agency (FEMA). Zones designated as special flood hazard areas on these FIRMs show where the probability of flooding is one percent or more in any particular year. Under Federal law mortgage lenders must require flood insurance coverage for properties in these areas. It’s important to note that ordinary homeowners insurance does not cover flood damage at all.

In order for Baltimore County to participate in the National Flood Insurance Program, under which our property owners may buy Federal flood insurance, we have to include certain provisions and restrictions in our building code and development regulations. Our Codes actually exceed Federal requirements; even before the most recent upgrades, no dwelling built in accordance with the Codes in effect at the time suffered significant damage during Storm Isabel in 2003.

The FIRMs show all of the tidal flood plains but generally only map riverine flood plains draining rainfall on areas of one square mile (640 acres) or greater. Baltimore County, however, prohibits development by right in flood plains draining areas of 30 acres or greater, and restricts construction adjacent to drainage courses of any size. The County has an inventory of flood plain studies that map flood plains with drainage areas smaller than those mapped on the FIRM.

The Codes allow new construction in tidal flood plains but do not allow new development by right in riverine flood plains. The County also uses the one-percent annual chance flood as our definition for flood plain regulation; however, we use a more conservative definition for riverine flood plains than does FEMA. FEMA bases its riverine flood plain limits on runoff calculated on existing land use, presumably to avoid overcharging insurance premiums. But the County bases its riverine flood plains on runoff calculated as if the drainage area were developed to the maximum allowed by zoning. Our reason is to prevent upstream development from putting properties into a flood plain area where one was not mapped previously. That is why building permits and land development projects in Baltimore County are subjected to restrictions greater than those shown on the FIRM. Our inventory of riverine flood studies will usually reflect this “ultimate” flood plain as well.

In the case of riverine flood plains, if the one percent annual chance flood plain has not been defined and mapped, a developer or permit applicant will be asked to submit a study prepared by a licensed engineer for that purpose.

Please refer to the following resources for the legal authority supporting our flood plain regulations:

  • Section 32.4.414 Baltimore County Code
  • Section 32.8 Baltimore County Code
  • County Council Bill 40-15 (Building Code, including the International Building Code and the International Residential Code by reference)
  • County Council Bill 42-15 (Adopting the Federal FIRMs and placing special requirements on the tidal flood plains for building code purposes)
  • Development Plan Review Policy Manual
  • Department of Public Works and Transportation Design Manual

Resources for Homeowners

FEMA Region III provides a pamphlet (PDF) advising homeowners of measures they can take to make their properties safer from flooding. FEMA also has additional online resources.

You can view FEMA flood plain data on the Baltimore County Digital Flood Insurance Rate Map (DFIRM), an online interactive application.

To report problems with any public storm drain system in your community, contact the Bureau of Engineering Storm Drain Design Division at 410-887-3711.

Contract of Sale Clause

The Department of Public Works and Transportation is frequently asked about language found in real estate sales contracts for properties offered for sale in Baltimore County due to the following section of Baltimore County Code:


(a) House removed from flood plain area. The following clause shall appear in any contract of sale or resale of a house, building, or other structure that has been removed from a 100-year flood plain area: "The house, building or structure which is the subject of this contract has been removed from a 100-year flood plain.

(b) Failure to include required language. Failure to include the clause mandated by this section shall render the contract voidable at the option of the purchaser.

This clause is about a very specific and unusual situation. The County on occasion will purchase properties subject to severe flooding as a less-expensive alternative to providing drainage improvements to streams. This is a rare occurrence, and even more rare is the situation where property owners like the house so much that rather than have it demolished, they have it placed on a special truck and moved to a new lot. If a house is “removed from a floodplain” in this way, the structure could have residual flooding damage that would not be expected in a house offered for sale in an area not designated as a flood plain.

Real estate settlements usually include a flood certification advising whether a house is located in a FIRM floodplain and for which flood insurance would have to be required by a mortgage lender, but that is something different.

Revised May 12, 2021         


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