Scope of Work Lower Arroyo Grande Creek …

1 Page 1 of 9 Scope of work Lower Arroyo Grande Creek flooding analysis Overview Please note that the limits of work for the hydrologic and hydraulic analysis include the following: Detailed topographic surveys: flood control portion of Arroyo Grande and Los Berros Creek and adjacent areas that would be impacted during a 100-year runoff event. See Figure 1 for details. Minor adjustments, such as including additional areas upstream on Los Berros Creek , can be made during the project initiation meeting and prior to scheduled aerial topographic survey flights. Hydrologic analysis : Hydrologic data will be developed for all areas of the Arroyo Grande Creek watershed downstream of Lopez Reservoir with the intent of providing necessary input parameters to the hydraulic model. Hydraulic analysis (HEC-RAS Model): The HEC-RAS model will be developed for the flood control portions of Arroyo Grande and Los Berros Creeks. The limits of work for the sediment source assessment and sediment transport analysis include the following: Sediment Source Assessment: The sediment source assessment will be developed for all areas of the Arroyo Grande Creek watershed downstream of Lopez Reservoir with the intent of providing necessary input parameters to estimate sediment supply, transport, and deposition conditions within the flood control portions of Arroyo Grande and Los Berros Creeks.

2 Sediment Transport analysis : Estimates of sediment flux, transport, and deposition using Parker (1990), or other appropriate methods, will be developed for the flood control portions of Arroyo Grande and Los Berros Creeks. As part of the proposed Scope we have solicited several bids from aerial survey firms to develop a high-resolution topographic map for the project area. Cannon Associates, a local San Luis Obispo County firm, provided the most complete and cost effective bid. A description of the services they will provide to the project is included. We are also pursuing a bid from Kellogg Aerials of Sacramento for aerial topographic mapping. Page 2 of 9 Task Descriptions Task 1 Topographic Data Collection Subtask : Aerial Topographic Data and Photos This task will be completed by an aerial survey firm to be determined at a later date following evaluation of additional cost estimates (Note: The bid listed in the cost estimate was submitted by Cannon Associates).

3 The primary objective will be to develop high resolution aerial topographic data of the study area, including lands to the north and south of the channel where flooding may result during a 100-year event. The study area also includes portions of the historic Los Berros Creek channel in the event that restoration of the old channel is considered as a component of one of the proposed alternatives. The aerial survey will consist of placing 35-40 aerial panels on the site to provide aerial control. Once the panels are set, the site will be photographed. A minimum of two overlapping photos will be taken. These photos will then be used to derive contours, features, roadways, etc. This information will be the basis for an AutoCAD drawing and 3-D model of the site. The aerial survey will be compiled according to the following specifications: Elevations will be represented with 10-foot index contours and 1-ft intermediate contours (accuracy of +/- feet).

4 Contours will be accurate to National Mapping Standards. Mapping will be produced at a scale of 1 = 40 . Coordinates and elevations will be based upon local county coordinates. Ortho-Rectified photos of the defined project area will be provided with a resolution of pixels, scanned at 15-18 microns and burned to a DVD or CD. Subtask : Refine topographic data Additional ground-based surveys will be conducted by SH+G engineers to refine the aerial-based survey around bridges, below water surfaces, and within thick vegetation. Supplemental information provided by the RCD and NRCS along the levees and within heavily vegetated areas will also be used. All information available from the ground-based surveys will be integrated into the aerial topo to produce a final topographic product that will be used to develop the HEC-RAS model. Task 2 Define Flood Reduction Alternatives Subtask : Define Water Surface Elevation (WSE) Flood Reduction Actions A set of actions will be compiled to reduce flood stage or reduce impacts associated with flooding on Arroyo Grande Creek .

5 These actions may include, but are not limited to, levee raises, levee setbacks, vegetation management, replacing bridges, or developing overflow weirs. The proposed actions will be developed in cooperation with stakeholders such as the RCD, NRCS, County of San Luis Obispo, landowners, residents, and permitting agencies. The initial set of potential actions will be based on a brainstorming meeting and will be comprehensive. Following compilation of a comprehensive list, SH+G will analyze each action item and reduce the list to those action items that are the most feasible in terms of engineering feasibility, cost effectiveness, and permitability. Project costs will be estimated based on preliminary concepts of the proposed action using similar projects as examples. The final list will be submitted to the RCD for review and comment by stakeholders. Page 3 of 9 Subtask : Sediment Reduction Management Actions Assuming that the results of our sediment budget and transport analysis (Task 4) suggest that sediment supply has accelerated due to anthropogenic influences, possibly requiring a long-term commitment to maintenance dredging, actions that will achieve a reduction in the supply of sediment to the flood control reach of Arroyo Grande Creek will be evaluated.

6 A range of sediment reducing actions will be developed during a brainstorming meeting with stakeholders. This comprehensive list will be evaluated and streamlined by SH+G staff based on engineering feasibility and the likelihood that the action would significantly reduce the supply of sediment. Rough cost estimates will be made for each item on the streamlined list of actions. The final list will be submitted to the RCD for review and comment by stakeholders. Subtask : Select Preferred Flood and Sediment Reduction Actions A Technical Advisory Team (TAT) meeting will be held to evaluate the results of the hydraulic and sediment transport analysis for each proposed action developed in Tasks and Each action will be evaluated based on the level of flood protection the action provides, the cost of the action, the engineering feasibility of the action, and the likelihood that the action could be implemented given budgetary and permitting constraints.

7 Based on the TAT s evaluation of each action a ranking will be assigned to each action defining a priority of implementation as high, medium, or low. The meeting will also include a discussion of potential funding sources and a phasing schedule to implement each action by priority ranking. Task 3 Hydraulic Modeling Subtask : Compile Site Hydrology Through a combination of existing data compilation ( Habitat Conservation Plan, CCSE Watershed Assessment, USACE HEC-RAS model) and analysis of discharge data for Arroyo Grande Creek , the hydrology for the site will be defined including the , 5-, 10-, 25-, 50-, and 100-year recurrence discharges. Hydrographs will be developed for each of these flood intervals as input to the HEC-RAS unsteady flow model. Where feasible, similar hydrologic parameters will be developed for streams tributary to the reach of interest (Los Berros channel). Subtask : Develop Existing Conditions HEC-RAS Model Both a steady and unsteady HEC-RAS model will be developed for Arroyo Grande Creek between Los Berros and the mouth and include all model elements including topography, bridge geometry, roughness characteristics, and input flow conditions.

8 Where feasible, the model will be calibrated using known discharge and stage conditions. The HEC model that is developed will be linked with Geo-RAS, an Arcview GIS based product that allows for 3-dimensional visual representation of flow depths and stage within the study area. SH+G will build on an existing HEC-RAS model developed for the Arroyo Grande Creek channel by the USACE in 2001, where feasible. The USACE model utilized historic cross-section and topographic data for development of the 2001 model, therefore, the topographic data will be replaced with the updated information generated from the aerial flights. Where feasible, model parameters such as roughness and discharge values will be carried over from the USACE model and comparisons will be made between Existing Conditions parameters between the two models. The USACE model will be a valuable tool to assess how the hydraulic character and sediment transport conditions have changed within the flood control channel in the intervening period of the two topographic datasets.

9 Page 4 of 9 Subtask : Existing Conditions flooding analysis The HEC-RAS model will be used to assess flood stage and volumes associated with the , 5-, 10-, 25-, 50-, and 100-year recurrence discharges. GIS layers will be generated to assess relationships between flooding during different events and land use and will include an analysis of flood impacts, tolerance, and risk. The following components will be included: Floodplain Subareas: Areas that will be subject to flooding will be identified and linked to their land use and level of development. Land use and level of development GIS layers will be provided by the RCD through San Luis Obispo County or appropriate city agencies. The floodplain subareas will be compiled onto GIS layers for each flooding scenario. flooding Impacts: For each sub-area identified above, an estimate of the financial impact on adjacent properties will be compiled into a GIS layer for each flooding scenario.

10 Data detailing crop values, property values (with land and structure values broken down), and the potential for lost income associated with business closings or access to property will be provided to SH+G on a per parcel basis by the RCD through San Luis Obispo County or appropriate city local agencies. flooding Tolerance and Risk: For each sub-area and flood scenario SH+G will document the tolerance to flooding (frequency, magnitude and duration) and convert the cumulative potential impact of flooding in each subarea to a ranking scale for each flood scenario. The purpose of the ranking scale is to prioritize mitigation project to reduce the extent of flooding based on frequency, magnitude, duration, and overall cost of potential damages. Subtask & : Develop HEC-RAS Model and Conduct flooding analysis for Proposed Actions This stage of the hydrologic and hydraulic analysis will consist of an iterative process that will result in a preliminary action plan to reduce flood impacts on Arroyo Grande Creek .