Is It Really an RPA – or Is That Stream Flowing Now? If you own land, or are planning to purchase land in a locality that has a Chesapeake Bay Preservation Ordinance, the answer to this question can make a difference in terms of how much of the property is suitable for development activities. In most of these localities, perennial streams1 and contiguous wetlands require an undisturbed 100-foot buffer on each side. If it is intermittent2 most localities do not require this buffer (note local rules do vary, and this is not true in Arlington, City of Fairfax, and Alexandria, for example) because the Commonwealth of Virginia only requires the RPA to include a 100-foot buffer around perennial streams. There are several protocols that can be used to determine whether a stream is perennial or intermittent. However, they are all subject to challenge and are not always conclusive. The only way to conclusively make the determination that a stream is intermittent instead of perennial is to observe the stream with no surface water flow in a non-drought period. Larger intermittent streams typically "go dry" in the July-September period, depending upon local storm influences, SWM/BMP releases, and industrial discharges (car washes and sump pump discharges can be influential in this period.) If you own property, you should observe any streams on your land and photograph the lack of flow, ideally having a non-related person in the photo who can attest to the time and date of the observation. You should summarize in writing the observation (persons present, date, time, location/direction of photo, non-drought data) and provide this to your land use attorney, civil engineer, or environmental consultant. Each locality has differing means of utilizing this data to make RPA determinations, but this "raw" data will help in all areas. Should I better document my stream flow if the locality's RPA map does not include my land? YES. Everyone should do this because: Many localities expanded the RPA definition – but did not modify their maps to show the expected increase in RPA coverage; The maps are just guidelines – only the text governs in most localities. So, the only way to know definitely is to observe your streams. Guidance from the Chesapeake Bay Local Assistance Department (CBLAD) recommends the use of the Palmer Drought Severity Index3 to determine if "non-drought" conditions are present. CBLAD guidance states that “Documented observations of no flow when the Palmer Drought Severity Index is wetter than a classification of -2.0 (moderate drought) should be considered definitive confirmation that the stream is not perennial.” If your property is in Fairfax County however, the Fairfax County Department of Public Works and Environmental Services (DPWES) prefers to use the U.S. Drought Monitor4 to determine if non-drought conditions exist. If you have any questions about RPAs and your property, you can contact: Mike Rolband, P.E., P.W.S. Mark Headly, P.W.S. Bill Nell, P.E. Craig Tumer, P.W.S. Laura A.B. Giese, Ph.D., C.F., P.W.S. Frank Graziano, P.E. Brian Chromey, P.E. Ian Smith, P.E. Dan Lucey, P.E. 1A perennial Stream has flowing water year-round during a typical year. The water table is located above the stream bed for most of the year. Groundwater is the primary source of water for stream flow. Runoff from rainfall is a supplemental source of water for stream flow. 2An intermittent stream has flowing water during certain times of the year when groundwater provides water for stream flow. During dry periods, intermittent streams may not have flowing water. Runoff from rainfall is a supplemental source of water for stream flow. 3The Palmer Drought Severity Index can be found on the following website: http://www.cpc.ncep.noaa.gov/products/monitoring_and_data/drought.html. 4Drought Monitor can be accessed at the following website: http://www.drought.unl.edu/dm/monitor.html.