Preliminary Basis of Design Report For South St. Vrain Creek Restoration at Hall Ranch September 2016 Submitted by: Prepared for: Boulder County, Colorado In association with: i Executive Summary (To Do: To be compiled once design has been finished) I certify to the best of my professional knowledge, judgment, and belief, these plans (or this report) meets applicable NRCS standards. 0 Table of Contents 1. Matrix Design Group Team Overview ...................................................................................................................... 6 2. Project Funding ......................................................................................................................................................... 6 3. Project Location ........................................................................................................................................................ 7 2013 Flood Impacts and Aftermath (Grant Application) ...................................................................................... 9 Post-Flood Repairs .............................................................................................................................................. 10 4. Project Goals and Objectives .................................................................................................................................. 11 Existing Goal Statements .................................................................................................................................... 11 i. RFP .................................................................................................................................................................. 11 ii. Grant Request ................................................................................................................................................. 11 iii. Master Plan ..................................................................................................................................................... 11 iv. Public Comments ............................................................................................................................................ 11 Project Goals Statement ..................................................................................................................................... 12 Project Objectives ............................................................................................................................................... 12 Emergency Watershed Protection Program ....................................................................................................... 12 5. Summary of Relevant Background Information ..................................................................................................... 13 Meeting with BCPOS ........................................................................................................................................... 13 LiDAR Mapping (2011 and 2014) ........................................................................................................................ 13 Post Flood Hydrology.......................................................................................................................................... 14 St Vrain Creek Watershed Master Plan .............................................................................................................. 14 Emergency Watershed Protection Program ....................................................................................................... 15 i. Damage Survey Report ................................................................................................................................... 15 ii. Project Engineering Guidance ........................................................................................................................ 15 iii. Preliminary Scope of Work ............................................................................................................................. 15 St Vrain Creek Channel Flood Recovery Design-Build Services .......................................................................... 16 St. Vrain Pipeline 2013 Flood Repair .................................................................................................................. 17 Meadow and South Ledge Diversion Reconstruction and Fish Passage Demonstration ................................... 17 County’s Management Plans .............................................................................................................................. 17 Public Comments ................................................................................................................................................ 18 6. Watershed Site Assessment Information ............................................................................................................... 18 Review of Existing Documentation ..................................................................................................................... 18 1 Survey ................................................................................................................................................................. 18 Riparian Assessment and Wetland Delineation ................................................................................................. 19 i. Existing Restoration Data ............................................................................................................................... 19 ii. Onsite Assessment ......................................................................................................................................... 25 Photo Documentation ........................................................................................................................................ 28 Base Map Development ..................................................................................................................................... 34 Site Inspection and Documentation ................................................................................................................... 35 i. Existing and Proposed Flood-Related Projects ............................................................................................... 35 ii. Existing and Proposed Non-Flood Related Projects ....................................................................................... 36 Soils Mapping ..................................................................................................................................................... 37 Field Sediment Sampling .................................................................................................................................... 37 i. In-situ Bed Load and Suspended Sediment Sampling .................................................................................... 37 ii. Bed and Bank Sediment Sampling .................................................................................................................. 39 7. Hydrology/Hydraulics Data..................................................................................................................................... 40 Hydrology ........................................................................................................................................................... 40 i. FEMA: Flood Insurance Study ......................................................................................................................... 41 ii. Blue Mountain Consultants: Geomorphic Indicators Paired with Discharges ............................................... 41 iii. CDOT Hydrologic Evaluation of the St Vrain Creek Watershed ...................................................................... 41 iv. St Vrain Creek Channel Flood Recovery Design-Build Services ...................................................................... 42 v. Hydrology Summary ....................................................................................................................................... 43 Preliminary Models ............................................................................................................................................ 44 i. 1D HEC-RAS Models (No Rise Analysis) .......................................................................................................... 44 ii. 2D SRH Models ............................................................................................................................................... 45 Results ................................................................................................................................................................ 46 Supporting Electronic Files ................................................................................................................................. 46 8. Geomorphology ...................................................................................................................................................... 47 Available Data ..................................................................................................................................................... 47 Geomorphic Assessment .................................................................................................................................... 49 i. Desktop Analysis ............................................................................................................................................