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I I I I I I I I I I I I I I I I I I I V-I SECT! ON V MASTER PLAN DEVELOPMENT ciated with the 100-year flood on Van Bibber Creek. The Ralston Creek and Leyden Creek phase B study was prepared by Wr; ght-McLaugh 1 in Engi neers. This study recommended improvements along Ralston Creek which could convey the 100-year flood within protected channel banks. No improvements were proposed in existing parks or areas which experienced little or no flood damage. The downstream portions of Leyden Creek also were to receive a channel which could convey the 100-year event. I NTRODUCTI ON The drainage basins of Ralston Creek, Leyden Creek and Van Bibber Creek are extremely diverse. The upstream portions of the basins, lying west of the hogback, are generally undeveloped and have rugged terrain. The areas east of the hogback are in a transitional stage. Small rural development exists in the high plains and foothills areas on the western portions of the basin east of the hogback. Intense residential and commercial development occurs in the downstream portions of the basin closer to Clear Creek. The City of Arvada adopted the recommendations made by the consultants in the Phase B reports and proceeded with a capital improvement program. A number of structures along Ralston Creek were improved to comply with the recommendations of the Master Plan. These structures include crossings at Carr Street, Lamar Street and Wadsworth Boul ev ard. Pri or to the construc- tion of Ward Road Reservoir it was decided that a reeval uation should be done of the Ralston/Leyden/Van Bibber Creek drainage basin to determine the impact of Ward Road Reservoir on the proposed improvements and the econo- mics of the reservoir construction. This 1985 study and design found that the Ward Road Reservoir could not be recommended over other alternatives avail abl e. Because of the 1 arge drai nage area west of the foothi 11 s and the intense development in the downstream portions of the basins, the area is subject to periodic flooding. As recently as the summer of 1984, Ralston Creek was observed to be flowing bank full. The intense development in the down- stream portion of the basins results in a high likelihood of extensive damages during flood events. In some cases encroachment has been so exten- sive that it has obliterated the historic channel. A prime example of this is the Arvada Plaza Shopping Center which was constructed over the mainstem of Van Bibber Creek. Floods would cause extensive damage in areas where this has occurred. The escalation of property values associated with in- flation and the anticipated future development upstream indicate that flood damages are not likely to decrease in the future. The Urban Drainage & Flood Control District, the City of Arvada, and Jeff- erson County have recognized the flood hazard in the past. In 1977, Phase B reports were published for Van Bibber and Ralston and Leyden Creeks. The report on Van Bibber Creek, prepared by Gingery Associates, Inc. recommend- ed the construction of a major reservoir on Van Bibber Creek near Ward Road. Their study indicated this facility, in conjunction with other im- provements recommended, significantly reduced the level of damages asso- PHASE A STUDY Purpose of the Phase A Study A principal purpose of this 1985 study was to con sol idate the previous master plans into one document encompassing Ralston Creek, Van Bibber Creek, and Leyden Creek and to improve on the information and analysis as necessary. This included the generation of hydrology on Van Bibber Creek with the methodology consistent with that used in the Ralston and Leyden Creek studies, to update damages associated with various floods and to determine the benefits of improvements made to the drainageway subsequent to the previous master plans. The establ ishment of a common survey datum was also a desire of the sponsors. Ward Road Reservoir was specified to be reevaluated. If Ward Road Reser- voir was shown to be economically unjustified, other alternates were to be dev i sed and ev a 1 uated.