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I I I I approximate-level hydraulic study of the Somh Plane River shortly after the Hayman Fire. FinalJ).. in the 3-mile reach from dO\l,llstream of Trumbull to upstream of Deckers. main channel data was derived from the existing USGSIFIS hydraulic model. Unfortunately, information regarding cross section location and configuration from the USGSIFIS model was not available at the time locations for new surveyed cross sections ".;ere being identified. Based on the assumption that the USGSIFIS model would be adequate for the purposes of the current study. no additional information was gathered in this reach. with the exception of the three bridges and their associated cross sections. Consequently, the relatively large cross section spacing that is apparent in several instances in the USGSIFIS model continues to be reflected in the current hydraulic model. The data sources used for each cross section are identified in Table 4.3. For the cross sections where the main channel was defined using the data contained in the USGSIFIS model. one of two vertical adjustments were made in the preparation of the current hydraulic model. The USGSIFIS model was prepared based on the !\GVD 1929 vertical datum. In order to convert main channel elevations to the NA VD 1988 vertical datum. all ground elevations were adjusted vertically by +3.67 feet. This is the conversion between NGVD and NA VD at Deckers. as determined by the \..idely recognized CorpsCon software. After making this vertical adjustment. it was found that six of the USGSIFIS cross sections appeared to be significantly lower than expected based on field observations. After the datum adjustment. these six cross sections still indicated the presence of relatively deep holes along the river. These holes were shown to be on the order of at least several feet. causing pools covering as much as one.quarter river mile. Field observations indicated a generally much smoother. monotonic bed profile. where pools of this size were not apparent. Consequently. additional vertical adjustments were made to theses sections by fitting them to the stream profile generated by adjacent cross sections. A brief summary of the adjustments made to the USGSIFIS cross sections is pro\'ided in Table 4.3. Detailed documentation of these cross sectional adjustments is included in Appendix E.I. I I I I I I I I I I I '*..4 Road CrossingslBridges I I A total of 11 bridges were identified within the study reach: one in the lower detailed reach. seven in the upper detailed reach. and three in the approximate reach. The geometry of each of the eight bridges within the two detailed study reaches was confirmed by observations and/or measurements taken during the field reconnaissance efforts completed for this study. However. in the course of evaluating the existing parameters for the three bridges in the USGS/FIS model. it was clear that elevation data contained in the USGSfFIS model for the three bridges was not consistent \\ith recent bridge survey data. field observations and LiDAR I I COCWCB03_South PhUlcJcpon_Joc 13 A,dutsO, eo"AhhG bGi'Hm.. he.