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observed data. The memorandum shall identify any remaining uncertainties and limitations of the model <br /> in order to guide the interpretation of the model results.The memorandum shall present the results of the <br /> model simulation of the lagoon under existing conditions. These results shall include an evaluation of the <br /> volumetric exchange rate befinreen the lagoon and the surrounding bay channels, and shall also identify <br /> locations which experience limited local tidal circulation. <br /> Task 3 PerForm Simulations of Proposed Lagoon Modifications <br /> Subtask 3-1 Develop Proposed Modifications <br /> The Consuitant shall assist the City with the development of potential modifications designed to enhance <br /> tidal exchange within the Lagoon. These modifications shall be developed with the aim of increasing the <br /> volumetric exchange rates, enhancing water quality, and reducing long-term maintenance such as <br /> aquatic vegetation growth and sediment accumulation. The Consultant shall provide the City staff with <br /> guidance and consultation based on our understanding of the physical processes and features which <br /> control mixing and circulation within the Lagoon, as informed by the field data collection and Existing <br /> Conditions simulation results as well as our past project experience working in similar tidal lagoon <br /> systems. <br /> Based on our initial assessment of the site, some potential hydraulic modifications which the City might <br /> consider are: <br /> • Modify operations of existing gravity structures and pumps <br /> • Add gravity discharge capaciry <br /> • Add pump capacity <br /> • Augment internal circulation w/flow diversion, new/increased connections, and/or <br /> mechanical circulation <br /> • Watershed source control and enhancement of stormwater BMPs such as low impact <br /> development(LID)techniques to reduce nutrient loading to the lagoon <br /> Consultant shall provide an engineering memorandum describing the proposed modifications. This <br /> memorandum shall inciude a general description of each set of modifications, including the location of <br /> any new or altered structures as well as notes on operating procedures for pumps, gates, and other <br /> adjustable hydraulic structures. This memorandum shali be submitted for review following the completion <br /> of Task 3-1. A revised version of the memorandum shall be submitted as an appendix of the Preliminary <br /> Engineering Report to be produced under Task 4. <br /> Subtask 3-2 Configure and Execute Simulations <br /> For the proposed modification scenarios identified in Subtask 3-1, Consultant shall configure the 2D <br /> hydraulic model to represent the modifications. We anticipate running at least five modification <br /> simulations ranging from relatively low-cost/low-impact changes to existing facilities, such as adjustments <br /> to existing pump station operations schedules, to more extensive lagoon modifications, such as the <br /> construction of new inlet and/or outlet structures, the construction of internal circulation enhancement <br /> structures, and the installation of new pump facilities. The simulations shall focus on conditions which <br /> pose the biggest water quality challenge, e.g. the fall and also consider future conditions with sea level <br /> REV:04-09-14 VR <br /> Page 12 of 16 <br /> ATTY/AG R.2014.048/E SA_88464 <br />