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I I I I I I I I I I ! I I I I I I I I I I ANALYSIS OF THE 1997 STORM EVENT The 1997 event occurred as a result of heavy rain on July 28, 1997. The storm resulted in as much as ten inches of rainfall during the evening from approximately five to eleven p.m, Figure 1 shows the rainfall totals that occurred during the event as compiled by the Colorado Climate Center. The raingage located near the Lory Student Center on the CSU main campus recorded that 5,30 inches of rain fell during the six hour period. The resulting runoff from campus and areas west of campus caused the damage. Generally, stormwater entered campus (Figure 2) at the intersection of Shields and Elizabeth Streets, and flowed eastward across the athletic field area, around the health services building, and into the lagoon area, library parking lot, Eddy Building, Education Building, and between Braiden and Aylesworth Halls, Ponding in this area inundated health services, Morgan Library, Lory Student Center, Eddy Building, Education Building and the southeast wing of Aylesworth Hall. Overflow from ponding flowed two directions. The first overflow area was along Pitkin Street to Center Avenue, then south on Center Avenue to Lake Street. The second overflow area was north of the Student Center and into the Engineering Building parking lot. The parking lot flow caused inundation of the Engineering Building and the Music Building. Water flowed east out of the engineering parking lot into the oval. The railroad embankment then held back the water, causing ponding in the oval up to eight feet deep, This inundated the Publication and Printing Building, the Occupation Therapy Building, Gibbons Building, the heating plant and Johnson Hall, Figure 2 also shows the 1997 flow as compared to the 1 OO-year flow at various locations on campus. Additionally, flow occurred along Pitkin and Lake Streets, and combined with water flowing south from the intersection of Pitkin and Braiden Drive. This water then flowed east to Center Avenue, and south to Lake Street. The water then flowed east along Lake Street, and south towards where the railroad tracks cross Prospect Road. This inundated the Forest Range Experiment Station parking lot. Figure 2 shows the buildings on campus that received damages from the storm. The map also shows the approximate limits of the inundation that occurred. The morning following the event, high-water levels on campus were marked and subsequently surveyed. Table 1 summarizes the documented elevations, and also compares the elevations to those for the 100-year event documented in the 1996 master plan. To evaluate the flow on campus and the effectiveness of the proposed drainage improvements, the SWMM hydrologic model for campus was used to simulate the event. The model was calibrated to match flow elevation measurements. The original model utilized for the master plan was modified to allow simulation of rainfall in excess of the 100- year storm. The modifications were primarily to extend the storage rating data of detention elements in the original model and to develop estimates of irrigation canal overtopping west of campus. In the master plan study, 100-year hydrographs were entered into the model for areas west of campus. The hydrographs were the results of simulated irrigation canal overtopping that occurred. Runoff from drainage west of campus is normally captured by the Pleasant Valley and Lake Canal, the New Mercer Canal, and the Larimer #2 Canal, These irrigation canals can carry runoff from frequent events, but cannot carry the runoff from larger events. As a result when the canals are overtopped, the runoff flows eastward towards campus, With the flow entering campus at the intersection of Shields and Elizabeth Streets, Figure 3 shows the general drainage areas and locations of canal overtopping that occurred. 2 Ayres Associates