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. ; SECTIO.POUR Problems and Needs The Level of Service provided by the current system is presented in Table 5. "Level of Service" for stormwater infrastructure is defined as the rainfall event that the system can accommodate without significant hazards or problems. This table illustrates hazards and problems with the Level of Service provided by the current system, in a generalized nature. Specific areas could be more hazardous and other areas less hazardous. The technical staff, using their best professional judgment and observations of recent flood events, developed this table. Table 5 Hazard Ratings for Current Level of Services Type of Hazard/Problem Level of Service bv ~'Rainfall Event in Years,,(l) 1 vear 2 vear I 10 vear I 50 vear I 100 vear Relative De2ree of Hazard Pedestrian Low Low Medium High High Traffic Medium Medium High High Hi2h Properly Dama ge Low Low Medium Hi2h Hi.h Structure Damage Low Low Low Medium High (1) Relation of "Rainfall Event in Years" to Percent Chance of Occurrence in One Year Rainfall Event in "Years" 1 I 2 I 10 I 50 I 100 Chance of Occurrence in One Year 100%+/- I 50% I 10% I 2% I 1%+/- It would be preferable to have a storm water system represented by a table with nothing but "Low" values in every cell. However, that is prohibitively expensive, and stormwater managers need to balance Level of Service with available funding. That is, an optimum level must be determined. The optimum Level of Service and associated funding will be determined with drainage basin planning studies that include cost/benefit analyses. 4.5 PHOTOGRAPHIC ILLUSTRA nON OF DRAINAGE PROBLEMS IN THE GRAND VALLEY The following photographs illustrate the need for maintenance, planning, and improved infrastructure for drainage in the Grand Valley. These photographs were taken by managers from the five entities, consultants, and individuals affected by flooding problems. Figures 3 through 6 i\lustrate maintenance needs varying from simple (trash removal) to more involved (utility relocation). Trash in a channel collects more trash and sediment and reduces the flow capacity of the channel. There is a need for systematic inspection and cleaning. Figure 6 illustrates overgrown vegetation as well as the potential problem of utility crossings. These crossings can be a hindrance to flow, and there may be issues with uncertain responsibilities for repairs or relocation. Figures 7 through 13 illustrate flooding and other issues. URS T:\PROJECTS\22236022_GAAND_VALlEY\SUB_00\6.0_PROJ_DELJV\F1NAL REPORT\FINAL REPT REV 4.DOC\9-JUl-03\\ 4-4