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<br />Another component includes the system that transports the storm <br />runoff from rare and major runoff events and has been termed the major <br />system, In many instances this system is unplanned and functions of <br />its own accord. More attention is currently being focused on the need <br />to plan for the functioning of the major system by physical works and <br /> <br />complimentary nonstructural measures, <br />The physical works begin at the urban lot which is graded to convey <br />stormwater to the street. The street is designed with curbs and gutters <br />to transport stonnwater along the edge of the roadways to the ,collector <br />system, The collector system is usually a network of underground <br />conduits that discharge into the main storm drains. which may not be <br />but are also usually underground. The'stormwater that accumulates from <br />a number of collector systems is then discharged through an outfan to <br />a major stream. In many systems the outfall discharges to remaining <br />small natural channels that have been modified to function as integral <br />parts of the storm drainage system, <br />In some instances the major drainage system has not been planned <br />or designed and therefore functions in unpredictable ways, In a large <br />number of cases, the initial drainage system is designed for a frequency <br />storm (say of 5-year exceedence interval) so that when a major runoff <br />event occurs, the stonnwater seeks the path of least resistence (which <br />is !!Q1 the stonn sewers), which llleilnS it flows cown streets, over curbs, <br />across yards, and at times through homes into old drainage channels. <br />Major events usually inflict great damage and cause considerQble <br /> <br />inconvenience in ul'ban areas. <br /> <br />" <br />:;) <br />