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I 49 I I I I I I The upper Bear Canyon Creek series of ponds Just below the NCAR property is particularly important because it is necessary to take off the top of the Bear Canyon Creek flood hydrograph as well as to minimize the flash- iness of the Fern Creek basin. Of particular importance is the sediment collecting capability of these ponds because it is well recognized that sediment movement was one of the major contributors to the disastrous 1969 flood On Bear Canyon Creek. The reader is referred to the photos In Section I I of this report. GENERAL NOTES Advantaqes of Flood Plain Zoninq. The low cost per mile of David's Draw reflects its early stage or urban- ization. It points out the advantages of planning for the waterway prior to urbanization by protection the flood plain from encroachment, using flood plain zoning to save the citizens money in the future. I I I I I I I I II ! I I I The County of Boulder has provided a great benefit to the City of Boulder, as well as to other cities and towns in the County, by adopting a good flood plain regulation recognizing the 100-year flood plain. The City of Bouider has a somewhat similar regulation so that the good created by the County is not lost after the area is annexed. The concurrent effort has created new opportunities for better urban development. Effects on Groundwater. The construction of these channels will lower and control the groundwater level in some adJacent areas, This will be beneficial. Prior to the construction of waterways, ground water elevation studies should be undertaken, Including the monitoring of wells, to preclude un- warranted claims by adjacent well owners that their well yields might have been adversely affected. Where adverse effects do occur, they should be anticipated and necessary arrangements made ahead of time. Soil Conservation Practices. A portion of cost for this proJect is necessary for control of sediment caused by erosion In the foothill basIns. The volume of sediment which would result from a maJor storm is of such magnitude that it would prob- ably cause problems even with the retention reservoirs contemplated. Boulder is indeed fortunate to have mountaIn parks and greenbelt land in the upper portIon of the basins. If the greenbelt land was to be developed, the downstream channel needs would be larger and more costly. APPLICABILITY OF MASTER PLAN The fact that the Drawings contained In Volume 2 are of a master plan nature must be kept in mind by all using this report. They are for planning purposes only and must not be used for construction purposes.