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<br />
<br />Rains from Hurricane Camiffe brought
<br />flooding to large areas 01 Virginia in
<br />August 1969. (Top, left) The James River
<br />at Richmond, two days after fhe record
<br />rainfall. (Top, right) After the flood,
<br />cleaning up an inundated store at
<br />Scottsville, Va. (Middle, left) The downM
<br />pour of 27 inches in eight hours carried
<br />away great patches 01 Virginia's hill-
<br />sides. (Middle, right, and lower left)
<br />Mud slides tumbled houses down
<br />hillsides and covered roads with muck.
<br />(Lower right) Fortunately, this home in
<br />Howardsville, Va., was unoccupied on
<br />the night of August 19-20, 1969.
<br />Photographs trom the Virginia Department of
<br />Highways. Charlollesville Daily Progress, Vir-
<br />ginia Department of Conservation and Economic
<br />Development. and the Richmond Times-Dispatch.
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<br />FLOOOS/FLASH FLOODS
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<br />Number of Floods and Flash Floods in Which American Red Cross Assistance Was Given, 195&-1971-data
<br />from American National Red Cross.
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<br />Q. When JOu S3}' a station is tclemetered. what does that mean?
<br />
<br />A. It means that observed amounts of precipitation or of stream
<br />level are telemetered to a \Veather Service office without a human
<br />observer being on the scene. To get the observation for a given
<br />spot, a man in the weather office dials a designated telephone num.
<br />ber for that gage and listens for a series of audible beeps separated
<br />by pauses. By counting the beeps in each series. he knows the level
<br />of water in a stream or the inches of water in a rain gage. For exam-
<br />ple, the first series of beeps might be three, then a pause, then four
<br />beeps, then a pause. then six beeps. So the number would be 346,
<br />which might indicate that a river was 34.6 feet above a certain stage.
<br />
<br />Q. That seems a hit cumbersome. Are there plans to speed the
<br />process?
<br />
<br />A. Yes, there are. The newer systems we'll be installing in a year
<br />or two will be automated so that the man at a station won't have to
<br />dial a number and count the beeps. The callMup will be made auto-
<br />matically and the information will be printed on a teletypewriter, so
<br />that the observer won't have to leave his radar screen. He will simply
<br />set this collection system in motion and refer to it from time to time
<br />to see what is happening at each gage.
<br />
<br />Q. Does radar help .You in locating areas of heavy rainfall?
<br />
<br />A. Yes, it does, and we are using radar more and more. Experi~
<br />ments are under way which will let llS get quantitative measurements
<br />from it. Until now, our use of radar has been qualitative. To under-
<br />stand the difference, you need to know how the traditional system
<br />works.
<br />By the traditional method, when the observer sees a very bright
<br />echo on his radarscope that tends to remain in the same place, geo-
<br />graphically, he may conclude that heavy rain is falling there, with a
<br />strong chance of flooding. He also may make a supplementary
<br />judgment based on cloud height~the higher the cloud top, the
<br />greater the precipitation.
<br />
<br />Q. But he doesn't really know how much precipitation?
<br />
<br />A. That's right. By conventional radar operation, he doesn't. We
<br />have tried to get around this problem at a dozen places in the East
<br />by clustering telemetered rain gages around radar stations. This sys-
<br />tem gives the radar observer a way to. relate what he sees on his
<br />scope to what is falling on the ground. If he sees a strong echo in a
<br />certain area, he interrogates a nearby rain gage and finds out what
<br />is happening. Then, using a map that indicates the areas that are
<br />prone to flash floods, he can alert appropriate localities that trouble
<br />is on the way.
<br />With this kind of radar umbrella over communities subject to
<br />flash floods, you have somebody watching over them all night long
<br />who has an idea of potential flash-flooding.
<br />
<br />And your ne\"', quantitati\'e system will be better?
<br />
<br />Q.
<br />
<br />A. Yes. It will involve an effort to put numbers~that is, inches of
<br />precipitation--{)n rainfall even before it hits the ground. It involves
<br />a new way of handling the radar information. We call it D! RADEX
<br />~for Digitized Radar Experiments. The heart of the system is a
<br />digitizer and a minicomputer connected to the radar.
<br />D/ RADEX is now being llsed experimentally in Oklahoma City;
<br />Fort \Vorth, Tex.: Kansas City, Mo., and Monett, Mo. Essentially it
<br />differs from the ordinary radar operation in that it gives YOll nu-
<br />merical values~from 1 through 9-for the strength of the echoes
<br />from a pattern of points inside a cloud system, instead of an image
<br />on a radar screen whose parts are of varying brightness. This means
<br />that the radar observer will be able to use numbers for what he sees,
<br />instead of having to resort to crude adjectives such as "intense" or
<br />"heavy" covering relatively large areas of rainfall.
<br />\Ve'lI have to spend some time calibrating the D/RADEX sys-
<br />tem, though-relating the l's through 9's to inches of rain~before
<br />wecanuseit.~willdothisbycompMi~~atitgivesus~fue
<br />results from our old system of rain gages which has been in use for
<br />so many years.
<br />
<br />e()ntitl~d
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