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I. 2 I I I I I I I I I I I SCOPE OF WORK The scope of work undertaken was to investigate alternative storm drain- age plans for the major drainage routes in South Boulder and to prepare comprehensive master plans for each of the waterways. The purpose of the plans is to provide sufficient information to permit local and state en- gineers to plan bridges and culverts for new streets, acquire necessary right-of-way, make allowances in new commercial, industrial, and resident- ial development, and to plan for future channel and flood plain limits, The master planning was limited to consideration of the major drainage system. The initial, or storm sewer system needs, was not included in the work. In urban drainage there are two storm runoff systems. The first is the major drainage system which is that route taken by flood waters whether or not drainageways have been planned or designed and whether or not build- ings and other improvements have been situated wisely in respect to the drainageways. In the Denver Region, the major drainage system should be reviewed and designed on the basis of storm runoff which would occur once each 100 years. The second system is what is known as the initial drain- age system. The initial drainage system generally consists of a combin- ation of storm sewers, streets, curbs and gutters, and other facilities sized to carry the storm runoff which can be expected about once each two to ten years. The initial drainage system is that which drains off snow- melt runoff, the more frequently expected storm runoff, and reduces street maintenance and construction costs. Poorly functioning initial systems are the ones which account for the great majority of drainage complaints to the city or county engineer, This master planning report deals only with the major drainage system. The major system is that which provides the major damage and loss of life prevention function, and which provides outfall points for the storm sewer systems. PROBLEMS OF THE AREA I The report presents a master plan for solving the major drainage problems of South Boulder. At the present time the well defined canyons and gulches leading out of the foothills lose their defined and incised character at the western edge of the City where the grade flattens somewhat, To com- plicate the problem, urban development has generally been done without full cognizance of the flood and debris hazard. Channel encroachment has been significant, I I 'I One gulch has not yet been subjected to urbanization, and here it is planned that no improvements will be made, The utilization of the Flood Plain Reg- ulation of the County of Boulder will be used instead, I I I PROCEDURE The procedure was to define the problem hydrologically and hydraulically by field and office studies, to developall practical alternates, and to study these alternates using a qualified environmental design team approach.