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City of Pleasanton | Stormwater System Management Plan | PWD 25.601 | PAGE 15 Task 3.4 – HWM Chalking and Calibration Without proper calibration, a model cannot be used confidently, and proposed improvements can be grossly oversized. A properly‐ calibrated hydrologic and hydraulic model will be consistent with and will match historical data, such as flow gage data, maintenance records, and anecdotal observations. The detailed models Wood Rodgers proposed in the tasks above will provide a platform to develop independent and soundly‐calibrated hydrologic and hydraulic parameters. Wood Rodgers proposes to collect high water marks for calibration within storm drain facilities at five locations. This approach provides peak recorded water levels that can be cost‐effectively used for calibration. The chalk mark locations will be selected at critical locations with known capacity deficiencies in order to aid calibration efforts and confirm the accuracy of hydrologic and hydraulic models. The collected high‐water marks will be used in conjunction with the stream gage data in Task 3.5 (if selected by the City) in the calibration task to validate the system’s performance. This information will confirm storm drain system deficiencies and result in optimized capital improvement projects. See Exhibit 12. As an optional subtask to Task 3.4, Wood Rodgers proposes installing, maintaining, and monitoring two rental gaging stations upstream of storm drain systems equipped with large trash capture devices. The City has been proactively inspecting and maintaining seven such devices to ensure proper system performance and prevent clogging that could reduce upstream storm drain conveyance capacity. These ongoing activities strain the City’s resources and make storm drain performance dependent on the City’s ability to respond promptly. To better understand the hydraulic performance of these devices and provide calibration data for their upstream storm drain systems, Wood Rodgers will use the collected data to calibrate both the devices and the upstream systems. The calibrated model could then be applied to evaluate potential improvements that would reduce the City’s maintenance requirements and flood risk. Deliverable(s): Quality checked rain gage (six) data | high water marks within storm drain facilities at five locations | Depth gage data at two locations for two years | Calibrated models for one wet season. Task 3.5 – Stream Gage Data Review and Calibration The Zone 7 open channels provide realistic tailwaters into which the City’s storm drain systems can discharge. This hydrodynamically‐ connected storm drain and open channel model reflects the actual hydraulic capacity, as well as the maintenance conditions, of these systems. To enhance the accuracy of the interaction between these facilities, Wood Rodgers proposes this optional task to collect and review stream gage data from Zone 7 for the calibration of the off‐site watersheds entering the City boundary. Hilly open space in the Bay Area typically contributes base‐flow and interflow after storm events. Wood Rodgers has successfully identified and calibrated catchments with substantial base‐flow and interflow using groundwater modeling features in software (see Exhibit 13). Our previous experience informs our work to further calibrate the catchments for City and Zone 7 facilities to reflect the actual base‐flow, interflow and the total storm peak flow, and to accurately reflect the actual performance of the flood system. Wood Rodgers will collect and quality‐check rain and stream gage data of one wet season for model calibration. The season with the highest peak flow from available gage data will be selected. Up to eight stream gages bordering the City’s boundary will be selected to record the flows entering and leaving the City’s boundary. Wood Rodgers will refine the model’s hydrologic and hydraulic parameters upstream of the four stream gages, iteratively using the quality‐checked recorded historical data to ensure accurate model performance. The intent is to refine the model parameters so that the model’s depth and flow results match the historical data before further analysis is conducted using hypothetical design storms as input. Deliverable(s): Quality checked rain and stream (4) gage data | Calibrated models for one wet season. Exhibit 12 Exhibit 13 EXHIBIT A Docusign Envelope ID: DF86282A-2A84-404C-9F8A-A035AEFBCFF8