February 1, 2022
Mr Rob Hingtgen
Land Use/Environmental Planner County of San Diego Planning and Development Services 5510 Overland Avenue San Diego, CA 92123
Subject: Sandia Creek Drive Bridge Replacement and Fish Passage Project PDS2020-LDGRMJ-30309; PDS2020-LDPIIP-60093; Log No. PDS2021-ER-21-02-005
Reference: Santa Margarita River Hydrology, Hydraulics and Sedimentation Study, dated July 2000, by WEST Consultants
Sandia Creek Drive Bridge Replacement Alternatives Analysis and 30% Design, dated February 2018, by River Focus
Hydraulic/Scour Report, dated May 2021, by River Focus
Mr. Hingtgen:
Thank you for the opportunity to comment on the referenced project on Sandia Creek Drive. For background, we have worked in the area for over 10 years, completing both a steelhead habitat assessment and the alternatives analysis reference above. We have had the good fortune to meet and befriend many locals and find the Santa Margarita River to be a hidden jewel of northern San Diego County. As advocates for open space and community we support fish passage projects, however, we have developed serious concerns regarding the project as proposed and want to share them with you and the local community. Our comments are intended in the spirit of the rigorous review necessary to complete a valid and competent project.
We have offered our concerns to both CalTrout and the CA Department of Fish and Wildlife; our apprehension lies not with the proposed bridge itself but in the flood flows that will affect Sandia Creek Drive downstream from the proposed bridge if it is constructed. Historical reporting and local experience, together with the evening news, all document that Sandia Creek Drive from the area of De Luz Road to the project site floods at the design criteria of the bridge. We have concluded that the proposed bridge will be inaccessible from the southern approach during large storms; from the north, the proposed bridge will deceptively facilitate access to a narrow and flooded canyon during 25-, 50-, and 100-year flood events Our work herein provides greater detail on the genesis of those concerns.
The Hydraulic/Scour Report contained in the CEQA document is of particular relevance to our concerns. Figure 1 reproduces the cover of that report. Note that the proposed bridge structure is in the lower right quadrant, and the lower left quadrant is downstream from the bridge.
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com
Figure 1. Cover Page from Hydraulic/Scour Report, River Focus, 2021
Please observe that the cover graphic is tightly cropped on the project location; of note is the hairpin turn the river completes in this reach. The 100-year flood flow is depicted in light blue overlay with the main channel depicted as a solid, dark blue line. In our earlier work on the project, we received another perspective of the 100-year flood flow from River Focus in an email dated November 10, 2017, and it is presented in Figure 2.
Figure 2: 100-year flood flow upstream and downstream of proposed CalTrout bridge, River Focus, 2017
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com
Figure 2 illustrates the base of our concern: in large flood flows, Sandia Creek Drive is flooded well downstream of the project site. That graphic indicates that the only portion of the riparian corridor that is not flooded is the rocky outcropping where the southern abutment of the proposed bridge is offered
In the report Sandia Creek Drive Bridge Replacement Alternatives Analysis and 30% Design, Appendix A contained the graphic produced by the civil/structural engineers for the project, Kpff. Like Figure 2, this graphic takes a landscape scale view of the project site; attention is directed to Sandia Creek Drive in the lower left of the graphic.
Figure 3: Option 1 Bridge Alignment and 100-year Flood Flows, Kpff and River Focus, 2018
Figures 2 and 3 are thus mutually supportive. Each of the figures shows a 2-D model of flood flow, each extends along Sandia Creek Drive to the south, and each shows appreciable flooding on that road in a 100-year flood. That flooding will impact local transportation and will require significant mitigation efforts. Of direct interest to our concern is that the graphic of the Hydraulic/Scour Report prepared by River Focus simply avoids the issue of downstream flooding by changing the scale of the graphics in figure 2 and figure 3.
More evidence of flooding downstream from the proposed bridge is presented in figure 7-3 of the Sandia Creek Drive Bridge Replacement Alternatives Analysis and 30% Design report; it shows a detail of the WEST report from 2000. That figure is duplicated below.
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com
Figure 4. WEST (2000) Model Cross Section Location Map
Note that there are cross sections noted in Figure 1, e.g., 105628. Those cross-sectional numbers correspond to the number of feet upstream from the mouth of the river; thus, section 105628 is 105,628 feet (or 20.0 miles) upstream from the mouth of the Santa Margarita River. Appendix H of that WEST report contained details of those cross sections, including surveyed elevations and modeling results, for the 10-, 50-, and 100-year flood events (and 25-year flood event by inference)
Figure 5: WEST (2000) HEC-RAS 1-D Model Cross Section results
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com
Taken together, the WEST hydrology report issued in 2000 and the River Focus data reported in 2017 and 2018 present documentation that Sandia Creek Drive floods significantly for approximately ½ mile downstream from the proposed bridge location. While the proposed bridge will clear span a small section of the river during flood events, separate reporting – compiled decades apart - documents that Sandia Creek Drive is inundated where that road parallels the river. The bridge will not be accessible from the south during significant flood events, and access from the north will funnel traffic directly into the flooded canyon.
The Hydraulic/Scour Report contained in the CEQA submittal presents a floodplain workmap that details the project area - but again omits the section of Sandia Creek Drive downstream from the project area that is inundated during floods. The authors characterize the red line as an approximate 100-year floodplain, but precision is again eschewed.
The Hydraulic Scour Report, then, does not state that Sandia Creek Drive does not flood between De Luz Road and the project site, it simply omits any consideration of that fact in its presentation. The solid red line that represents the 100-year flood flow, however, is presented downslope from Sandia Creek Drive in the lower left quadrant. This FEMA flood delineation is characterized as ‘approximate’ in the report and is insufficient to appropriately define flood hazards on Sandia Creek Drive.
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com
The photo illustration in Figure 7 synthesizes the concerns raised in this submittal; the photo was taken on February 14, 2019. That flood peaked at roughly 22,000 cubic feet per second (about a 25-year flood), and we know from the work of River Focus, WEST, personal observation, and local news reporting that Sandia Creek Drive was heavily inundated (although the news reporter mispronounces Sandia Creek Drive). The cars in the lower right quadrant cannot cross the river, but they parallel the river, outside of the floodway, in a location of relative safety.
This is where the counterintuitive safety characteristic of the existing, flooded bridge becomes evident: that ephemeral obstruction keeps southbound traffic on the north side of the river, out of the canyon, during high flood events Construction of the proposed bridge will allow unobstructed access from the north, across the Santa Margarita River at high flood flows. After crossing that bridge from the north, however, vehicular traffic will proceed directly into the flooded narrow canyon, where the road closely parallels the river. Egress from that area in high flood flows would be nearly impossible; that road section has no shoulder and the only way out would be back over the bridge. Finally, the proposed bridge will be inaccessible from the south during high flood flows due to the referenced flooding along Sandia Creek Drive.
Figure 7: February 14, 2019, flood (facing downstream, northeast to southwest). If the pictured vehicles cross the proposed bridge into the narrows, they are doomed.
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com
1) Contained in the Initial Study, number XVII, the document asks:
XVII. TRANSPORTATION. Would the project: a) Conflict with a program plan, ordinance or policy addressing the circulation system, including transit, roadway, bicycle and pedestrian facilities?
The project proponent states:
”The new bridge will also make travel safer during flood events by decreasing the potential for overtopping by elevating the roadway and bridge to accommodate a 100-year flow event with one foot of freeboard as required by the San Diego County Hydraulic Design Manual”.
Comment: Travel can only be considered safer if the flooding on Sandia Creek Drive between De Luz Road and the project site is not considered. Several data sets referenced herein document that flooding, and the bridge will be unreachable from the south during large storms. The real danger of the proposed bridge is to vehicles that cross the river from the north during large storms, as shown in figure 7. Those vehicles will unsuspectingly find themselves on a flooded road, paralleling a raging river, with no direct means of egress. This will be a significant impact.
Recommendations for mitigation of the Significant Impact
A. Vertical realignment of Sandia Creek Drive between De Luz Road and the project site.
To ensure safe travel during the 100-year flood event, Sandia Creek Drive needs to be vertically realigned in areas that are within the 100-year floodway. This can be accomplished by constructing levees or another form of elevated roadway from De Luz Road to the project site, as determined to be necessary. That realignment may require condemnation of existing private property along Sandia Creek Drive and will likely encroach on San Diego County’s Santa Margarita River Preserve.
Construction of the vertical realignment will necessitate closing Sandia Creek Drive for the duration of construction. Due to threatened and endangered species in the area construction activities are limited by the US Fish and Wildlife Service to fall/winter months, approximately September through March. That would serve to effectively double the annual construction schedule Vertical realignment as a mitigation may, however, be inconsistent with the CEQA prohibition on piecemealing. Because the proposed bridge itself will not provide safe travel in 100-year flood events, the vertical realignment of Sandia Creek Drive may be considered an essential element of “the whole of the action” for the proposed bridge project.
B. Modification of the existing bridge on Sandia Creek Drive to facilitate fish passage.
The existing box culvert structure on Sandia Creek Drive has been characterized as a partial barrier to fish passage and is less than a formidable barrier. That structure could be modified to allow for fish passage at low flows for a small fraction of the proposed bridge costs and result in a swift and safe outcome for all.
Sincerely, Robert Blankenship, B.A. Trout Unlimited – South Coast 923
South Coast Chapter 3154 Glendale Blvd. #117 Los Angeles, CA 90039 SouthCoastTU@gmail.com www.SouthCoastTU.com