Flood Protection Planning Study for the Fredericksburg Area
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FLOOD PROTECTION PLANNING STUDY FOR THE FREDERICKSBURG AREA TEXAS WATER DEVELOPMENT BOARD Research and Planning Fund TWDB Contract No. 96-483-161 August 1997 prepared for CITY OF FREDERICKSBURG Gillespie County, Texas prepared by R. J. BRANDES COMPANY Austin, Texas FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company TABLE OF CONTENTS 1.0 INTRODUCTION 1-1 1.1 STUDY OVERVIEW 1-1 1.2 STUDY PARTICIPANTS 1-1 1.3 STUDY BACKGROUND 1-1 1.4 PLANNING AREA 1-4 2.0 OAT A AND INFORMATION 2-1 2.1 EXISTING SOURCES 2-1 2.2 FIELD SURVEYS 2-3 2.3 GILLESPIE COUNTY FLOOD INSURANCE STUDY 2-3 3.0 FLOOD FLOW CONDITIONS 3-1 3.1 PREVIOUS FLOOD INSURANCE STUDY 3-1 3.2 HEC-1 HYDROLOGIC ANALYSES 3-1 3.2.1 HEC-1 Model Application 3-2 3.2.2 Rainfall Statistics 3-4 3.2.3 Critical Storm Duration 3-5 3.2.4 Peak Flood Flows 3-6 3.3 LOCALIZED RUNOFF ANALYSES 3-7 4.0 STREAM HYDRAULIC ANALYSES 4-1 4.1 STREAM MODEL DEVELOPMENT 4-1 4.2 BARONS CREEK HEC-2 ANALYSIS 4-2 - 1 - FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company TABLE OF CONTENTS 4.3 TOWN CREEK HEC-2 ANALYSIS 4-4 4.4 STREAM FB-1 HEC-2 ANALYSIS 4-6 5.0 EXISTING FLOODING PROBLEMS 5-1 5.1 LOCALIZED FLOODING 5-1 5.1.1 Friendship Lane Drainage 5-4 5.1.2 Schubert Street Pending 5-5 5.1.3 Cross Mountain - Milam Drainage 5-6 5.1.4 Burbank - Llano Drainage 5-7 5.1.5 North Lincoln Drainage 5-8 5.1.6 College - Llano Drainage 5-8 5.1.7 College - Travis Drainage 5-8 5.1.8 Trailmoor Drainage 5-10 5.1.9 Morning Glory - Llano Drainage 5-10 5.1.10 Carriage Hills Drainage 5-10 5.1.11 West Creek Street Drainage 5-12 5.1.12 Old Harper Road Drainage 5-12 5.1.13 Winfried Creek Drainage 5-12 5.1.14 Five Points Area 5-13 5.1.15 South Adams Drainage 5-13 5.1.16 Highway - Apple Drainage 5-14 5.1.17 Dry Creek Drainage 5-14 5.2 STREAM FLOODING 5-15 5.2.1 Barons Creek 5-15 5.2.1.1 Wastewater Treatment Plant to 5-15 Goehmann Road 5.2.1.2 Upstream of F. M. 1631 5-16 5.2.1.3 Lincoln to Adams Reach 5-16 5.2.1.4 South Bowie Street 5-17 5.2.2 Town Creek 5-18 5.2.2.1 Elk Street 5-18 • 2. FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Soard Research and Planning Fund City of Fredericksburg R. J. Brandes Company TABLE OF CONTENTS 5.2.2.2 Crockett Street 5-18 5.2.2.3 Orange Street 5-19 5.2.2.4 Edison-Schubert Streets 5-19 5.2.3 Stream FB-1 5-20 5.3 ROADWAY FLOODING 5-21 6.0 DRAINAGE IMPROVEMENT AND FLOOD PROTECTION 6-1 ALTERNATIVES 6.1 LOCALIZED FLOODING 6-1 6.1.1 Friendship Lane Drainage 6-3 6.1.2 Schubert Street Pending 6-8 6.1.3 Cross Mountain - Milam Drainage 6-9 6.1.4 Burbank - Llano Drainage 6-10 6.1.5 North Lincoln Drainage 6-10 6.1.6 College - Llano Drainage 6-11 6.1.7 College - Travis Drainage 6-11 6.1.8 Trailmoor Drainage 6-12 6.1.9 Morning Glory - Llano Drainage 6-12 6.1.10 Carriage Hills Drainage 6-13 6.1.11 West Creek Street Drainage 6-15 6.1.12 Old Harper Road Drainage 6-15 6.1.13 Winfried Creek Drainage 6-16 6.1.14 Five Points Area 6-16 6.1.15 South Adams Drainage 6-17 6.1.16 Highway - Apple Drainage 6-17 6.1.17 Dry Creek Drainage 6-17 6.2 STREAM FLOODING 6-18 6.2.1 Town Creek 6-18 6.2.2 Stream FB-1 6-19 6.3 REGIONAL DETENTION PONDS 6-20 6.3.1 Town Creek 6-20 - 3 - FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company TABLE OF CONTENTS 6.3.2 Barons Creek 6-22 6.3.3 Stream FB-1 6-23 7.0 DRAINAGE AND FLOOD PROTECTION ORDINANCES 7-1 8.0 DRAINAGE IMPROVEMENT AND FLOOD PROTECTION PLAN 8-1 8.1 LOCALIZED FLOODING PLAN 8-1 8.1.1 Friendship Lane Drainage 8-3 8.1.2 Schubert Street Pending 8-3 8.1.3 Cross Mountain - Milam Drainage 8-4 8.1.4 Burbank - Llano Drainage 8-4 8.1.5 North Lincoln Drainage 8-4 8.1.6 College - Llano Drainage 8-4 8.1.7 College - Travis Drainage 8-5 8.1.8 Trailmoor Drainage 8-5 8.1.9 Morning Glory - Llano Drainage 8-5 8.1.10 Carriage Hills Drainage 8-5 8.1.11 West Creek Street Drainage 8-5 8.1.12 Old Harper Road Drainage 8-5 8.1.13 Winfried Creek Drainage 8-6 8.1.14 Five Points Area 8-6 8.1.15 South Adams Drainage 8-6 8.1.16 Highway - Apple Drainage 8-6 8.1.17 Dry Creek Drainage 8-6 8.2 STREAM FLOODING PLAN 8-6 8.2.1 Town Creek 8-7 8.2.2 Stream FB-1 8-8 - 4 - FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredetlcksburg R. J. Brandes Company LIST OF TABLES TABLE 2-1 INVENTORY OF FIELD SURVEY SITES TABLE 3-1 EFFECTIVE FLOOD INSURANCE STUDY PEAK FLOOD FLOWS TABLE 3-2 HYDROLOGIC PARAMETERS FOR HEC-1 MODEL SUBWATERSHEDS TABLE 3-3 EXAMPLE SOIL CONSERVATION SERVICE CURVE NUMBER CALCULATIONS TABLE 3-4 GENERALIZED LAND USE AND CURVE NUMBER ASSIGNMENTS FOR EXISTING CONDITIONS WATERSHED TABLE 3-5 GENERALIZED LAND USE AND CURVE NUMBER ASSIGNMENTS FOR FUTURE CONDITIONS WATERSHED TABLE 3-6 RAINFALL DEPTHS AND INTENSITIES FOR FREDERICKSBURG, TEXAS TABLE 3-7 HEC-1 MODEL 1 00-YEAR FLOOD FLOWS FOR DIFFERENT STORM DURATIONS TABLE 3-8 HEC-1 MODEL FLOOD FLOWS FOR EXISTING AND FUTURE WATERSHED CONDITIONS TABLE 3-9 LOCALIZED AREA FLOODING ANALYSIS TABLE 4-1 BARONS CREEK 1 00-YEAR FLOOD HEC-2 WATER SURFACE ELEVATIONS TABLE 4-2 TOWN CREEK 100-YEAR FLOOD HEC-2 WATER SURFACE ELEVATIONS - 5 - FLOOD PROTECnON PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company LIST OF TABLES TABLE 4-3 STREAM FB-1100-YEAR FLOOD HEC-2 WATER SURFACE ELEVATIONS TABLE 5-1 LOCALIZED FLOODING PROBLEM SITES TABLE 5-2 STREET AND CHANNEL FLOODING DEPTHS TABLE 5-3 LIST OF ROAD CROSSINGS AND ASSOCIATED FLOODWATER ELEVATIONS TABLE 6-1 ALTERNATIVES FOR LOCALIZED DRAINAGE IMPROVEMENTS AND FLOOD CONTROL MEASURES TABLE 8-1 LOCALIZED FLOODING RECOMMENDED ALTERNATIVES TABLE 8-2 LONG-TERM DRAINAGE IMPROVEMENT ALTERNATIVES TABLE 8-3 RECOMMENDED STREAM FLOOD PROTECTION ALTERNATIVES TABLE 8-4 LONG-TERM STREAM FLOOD PROTECTION ALTERNATIVES - 6 - FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company LIST OF FIGURES FIGURE 1-1 FLOOD PROTECTION PLANNING AREA FIGURE 2-1 CORPS OF ENGINEERS GILLESPIE COUNTY FLOOD INSURANCE STUDY HEC-2 MODELS FIGURE 3-1 EFFECTIVE FLOOD INSURANCE STUDY HEC-2 MODELS FIGURE 3-2 RAINFALL DURATION-INTENSITY CURVE FOR FREDERICKSBURG FIGURE 4-1 FLOOD PROTECTION PLANNING STUDY REVISED HEC-2 MODELS FIGURE 4-2 BARONS CREEK 100-YEAR FLOOD HEC-2 WATER SURFACE PROFILES FIGURE 4-3 BARONS CREEK 100-YEAR FLOOD HEC-2 WATER SURFACE PROFILES FIGURE 4-4 TOWN CREEK 100-YEAR FLOOD HEC-2 WATER SURFACE PROFILES FIGURE 4-5 TOWN CREEK 100-YEAR FLOOD HEC-2 WATER SURFACE PROFILES FIGURE 4-6 STREAM FB-1 100-YEAR FLOOD HEC-2 WATER SURFACE PROFILES FIGURE 4-7 STREAM FB-1 100-YEAR FLOOD HEC-2 WATER SURFACE PROFILES FIGURE 5-1 BARONS CREEK 100-YEAR FLOODPLAIN BOUNDARIES UPSTREAM OF CITY WASTEWATER TREATMENT PLANT FIGURE 5-2 TOWN CREEK 100-YEAR FLOODPLAIN BOUNDARIES UPSTREAM OF ELK STREET - 7- FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company LIST OF FIGURES FIGURE 5-3 TOWN CREEK 100-YEAR FLOODPLAIN BOUNDARIES UPSTREAM OF CROCKETT STREET FIGURE 5-4 STREAM FB-1 1 00-YEAR FLOODPLAIN BOUNDARIES THROUGH CARRIAGE HILLS SUBDIVISION - 8 - FLOOD PROTECTION PLANNING FOR THE FREDERICKSBURG AREA Texas Water Development Board Research and Planning Fund City of Fredericksburg R. J. Brandes Company LIST OF PLATES PLATE 3-1 MAP OF HEC-1 MODEL SUBWATERSHEDS PLATE 3-2 MAP OF LOCALIZED FLOODING PROBLEM AREAS PLATE 5-1 MAP OF LOCALIZED FLOODING PROBLEM SITES PLATE 5-2 MAP OF LOCALIZED FLOODING PROBLEM SURVEY SITES PLATE 6-1 MAP OF DRAINAGE AND FLOOD PROTECTION ALTERNATIVES PLATE 8-1 MAP OF DRAINAGE AND FLOOD PROTECTION PLAN - 9 - 1.0 INTRODUCTION 1.1 STUDY OVERVIEW This regional Flood Protection Planning Study has been undertaken to provide an evaluation of existing flooding conditions and needed drainage improvements and flood control measures within the City of Fredericksburg and adjacent areas of Gillespie County. The study has focused on localized solutions to existing and projected flooding problems, as well as, regional control measures such as stormwater detention facilities.