Res 2013-124/Approving an agreement between the City and Espey Consultants, Inc. in connection with the Comprehensive Watershed Master Plan

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— L�2e B : Hydrology from the GBRA study will be utilized where possible. The only watershed that is not covered in the GBRA study is Cottonwood Creek Watershed (9.8 square miles). A new hydrologic model will be developed for this watershed using the GBRA methodology. 3.2. Hydrologic Report: Following the completion of all hydrologic tasks, a hydrologic report will be generated for use in the drainage master plan. This report will include documentation of methodologies, assumptions and results for all San Marcos watersheds. TASK 4: HYDRAULIC ANALYSIS The hydraulic analysis effort will be encapsulated by streams listed in Table 1. Hydraulic analysis shall be conducted in accordance to FEMA and City of San Marcos guidelines and specifications. The deliverables per frequency are displayed in Table 2. Table 2. Frequency Requirements 4.1. Hydraulic Modeling: Develop hydraulic models for the existing and ultimate condition 2 -, 5 -, 10 -, 25- , 50 -, 100 -, 250 -, and 500 -year events. All approaches will be consistent with the GBRA methodology. — Types A: The hydraulics for these streams will be generated under the GBRA project. No new analysis is necessary. — Type B : Since these streams were studied in 2007 using the 2003 LiDAR and 2005 survey data, these models will only require an update. The 2007 geospatial cross - sections will be re -cut on the new 2006 -2009 LiDAR. Coded structures will not be revised unless necessary. New GBRA and Cottonwood Creek flow rates will also be incorporated into the HEC -RAS models. Minor model adjustments may be necessary with the addition of new topography and flow rates. These streams include 15.67 miles of updated detailed hydraulic analysis. — Type C : There are currently FEMA floodplains along these streams, however no recent studies have been performed. New detailed analysis (with survey) for 3.5 stream miles along PC -1 and Willow Springs Creek and limited detailed (without survey) analysis for 2.46 stream miles along UNT to PC will be prepared. 4.2. Floodplains: Delineate floodplains for the existing and ultimate condition 10 -, 25 -, and 100 -year events. These floodplains will be delineated using FEA/Lr standards. — Type A : Floodplains will be delineated for all events except the existing condition 100 -year event because it will be generated in the GBRA project. — Types B and C : Floodplains for the existing and ultimate condition 10 -, 25 -, and 100 -year events will be delineated. 4.3. Profiles: Develop profiles for the existing and ultimate condition 10 -, 25 -, and 100 -year events. To generate consistency, profiles for all study type designations (r�, B and C) will be developed. 4.4. Hydraulic Report: Following the completion of all hydraulic modeling tasks, a hydraulic report will be generated for use in the drainage master plan. This report will include documentation of methodologies, assumptions and results for all streams listed in Table 1. 4.5. Flood Mitigation Analysis: Perform flood mitigation analysis by identifying and analyzing projects to help reduce flooding. mom Page 4of10 mom HALFF+ Existing Condition Frequency Events 20 -year Future Condition equencV Events 2- 5- 10- 25- 50- 100- 250- 500- 2- 5- 10- 25- 50- 100- 250- 500 - Hydrolo y Models ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ H draulicModels ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Floodplains ✓ ✓ ✓ ✓ ✓ ✓ Profiles ✓ ✓ ✓ ✓ ✓ ✓ 4.1. Hydraulic Modeling: Develop hydraulic models for the existing and ultimate condition 2 -, 5 -, 10 -, 25- , 50 -, 100 -, 250 -, and 500 -year events. All approaches will be consistent with the GBRA methodology. — Types A: The hydraulics for these streams will be generated under the GBRA project. No new analysis is necessary. — Type B : Since these streams were studied in 2007 using the 2003 LiDAR and 2005 survey data, these models will only require an update. The 2007 geospatial cross - sections will be re -cut on the new 2006 -2009 LiDAR. Coded structures will not be revised unless necessary. New GBRA and Cottonwood Creek flow rates will also be incorporated into the HEC -RAS models. Minor model adjustments may be necessary with the addition of new topography and flow rates. These streams include 15.67 miles of updated detailed hydraulic analysis. — Type C : There are currently FEMA floodplains along these streams, however no recent studies have been performed. New detailed analysis (with survey) for 3.5 stream miles along PC -1 and Willow Springs Creek and limited detailed (without survey) analysis for 2.46 stream miles along UNT to PC will be prepared. 4.2. Floodplains: Delineate floodplains for the existing and ultimate condition 10 -, 25 -, and 100 -year events. These floodplains will be delineated using FEA/Lr standards. — Type A : Floodplains will be delineated for all events except the existing condition 100 -year event because it will be generated in the GBRA project. — Types B and C : Floodplains for the existing and ultimate condition 10 -, 25 -, and 100 -year events will be delineated. 4.3. Profiles: Develop profiles for the existing and ultimate condition 10 -, 25 -, and 100 -year events. To generate consistency, profiles for all study type designations (r�, B and C) will be developed. 4.4. Hydraulic Report: Following the completion of all hydraulic modeling tasks, a hydraulic report will be generated for use in the drainage master plan. This report will include documentation of methodologies, assumptions and results for all streams listed in Table 1. 4.5. Flood Mitigation Analysis: Perform flood mitigation analysis by identifying and analyzing projects to help reduce flooding. mom Page 4of10 mom HALFF+