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<br />l'fplcaltloodatagehydrograph <br /> <br /> I . I <br /> , <br /> ! <br /> I '\ I I <br /> \Ir~ " , <br /> /' . <br /> !j ,~ <br /> II \.' <br /> , \ <br /> I \ .\ <br /> ,.., ~ril1968~' <br /> I , <br /> H: " , <br />~, \ \ <br /> , \ 1\ <br /> \ <br /> ! <br /> , , I ' '\ <br /> , ',\ <br /> , F100dstle <br />, . -, '~ <br />, <br /> <br />" <br /> <br />" <br /> <br />" <br /> <br />" <br /> <br />l <br />. <br />.i 2C <br />f <br />; <br /> <br />'" <br /> <br />'" <br /> <br />" <br /> <br />., <br /> <br />, <br />April <br /> <br />" <br /> <br />" <br /> <br />" <br /> <br />A hydro graph charts water <br />depth in relation to time, <br />indicating the rate at which <br />flood water will rise and <br />fall. This information is <br />useful in determining the <br />amount of advance warn- <br />ing likely and the duration <br />of flooding <br /> <br />44 <br /> <br />" <br /> <br />" <br /> <br />, <br />"" <br /> <br />Water pressure, hoth above <br />and below the ground, is <br />increased by the rise of <br />flood water. 7bis pressure <br />causes increased stress on <br />buildings'foundations, <br />footings, and floor slabs. <br /> <br />'" <br /> <br />". <br /> <br />~ <br />700 ~ <br />" <br />oj <br />. <br />'" 1 <br />l <br />o <br />MI <br /> <br />"" <br /> <br />'00 <br /> <br />'" <br /> <br />niques that require time to install. It is also a factor in <br />designing systems for wet floodproofing and influences <br />the design of drainage systems. <br />Data on rates of rise and fali of water is typically <br />presented in the form of a hydrograph, which charts <br />water depth over time, and is part of many of the tech- <br />nical reports. In addition to the usuai sources, data on <br />warning time may be avaiiabie from local civii defense <br />offices or the historical records of locai police or fire <br />departments. <br />Duration of Flooding The duration of flood inun- <br />dation, which is a function of the rate of rise and fall of <br />water, has several important influences on design. Dura- <br />tion influences the saturation of soiis and buiiding mate- <br />rials, the amount of seepage, and the length of time that <br />faciiities might be inaccessable or inoperable, which <br />might have major economic impacts. These factors can <br />affect design decisions on buiiding orientation, config- <br />uration, and use of the various floodproofing tech- <br />niques. The various floodplain technical studies and his- <br />torical records are the sources for this information. <br />Frequency of Flooding The frequency with which <br />flooding occurs is of course a major factor in determin- <br />ing buiiding locations. It can also be important in con- <br />sidering techniques for floodproofing, particularly those <br />that require installation prior to each flood event. For <br /> <br />