FLOOD08569

• Designation Number: 574
• County: Jefferson
• Community: Arvada
• Stream Name: Ralston Creek and Leyden Creek
• Basin: South Platte
• Title: FHAD - Ralston Creek and Leyden Creek
• Date: 6/1/2004
• Prepared For: Douglas County, Arvada
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

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TABLE OF CONTENTS

SECTION 1.0 - INTRODUCTION .......................................".......................................................1

1.1 Authorization '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''....................,......... 1

1.2 Purpose and Scope......................................................................................... 1

1.3 Watershed Study History ...............................................................................1
1.4 Floodplain History .........................................................................................1
1.5 Background Information................................................................................2
1.6 FHAD Mapping Information......................................................................... 2
1.7 Survey Information........................................................................................ 2

1.8 Acknowledgements...... ............ .......... ......... ................................................ ... 2

4.5 Description of Reaches ................................................................................10

4.6 Floodplain and Floodway Data.................................................................... 11

4.7 Flood Velocities........................................................................................... 12

SECTION 5.0 - REFERENCES ................................................................................................... 24

LIST OF FIGURES

Figure 1
Figure 2
Figure 3

Watershed Delineation - Overall Drainage Area........................... ................4
Ralston Creek Peak Discharge Profiles... '" ............ ... ............... ............ ......7
Leyden Creek Peak Discharge Profiles..................... ............... ............... ...8

SECTION 2.0 - DRAINAGE BASIN CHARACTERISTICS ....................................................... 3

LIST OF TABLES

2.1 Location ......................................................................................................... 3

2.2 Topography and Physiography...................................................................... 3

2.3 Flood History .................................................................................................3

2.4 Flood Related Studies .................................................................................... 3

Table 1
Table 2
Table 3
Table 4
Table 5

SECTION 3.0 - HYDROLOGIC ANALYSIS ............................................................................... 5

Ralston Watershed - Hydraulic Summary Table...........................................9
Ralston Creek Floodplain Data for 10-, 50-, and 500-YearFlows................13 - 17
Ralston Creek Floodplain and Floodway Data Table for 100- Y ear Discharges. 18 - 21
Leyden Creek Floodplain Data for 10-, 50-, and 500- Year Flows..................... .22
Leyden Creek Floodplain and Floodway Data Table for 100- Year Discharges..... .23

APPENDIX

3.1 General......... ...................... .............. .......................................... ... ....... .......... 5

3.2 Background...................................... .......... ............ .............. ...... .......... ....... ... 5

3.3 Subwatershed Delineation ............................................................................. 5
3.4 Watershed Imperviousness ............................................................................ 5
3.5 Soils Information ........................................................................................... 5

3.6 Rainfall............................... ........... ............. ...................... ....... ............... .... ....5

3.7 Regional Reservoirs ....................................................................................... 6

3.8 Peak Flows ..................................................................................................... 6

Flood Hazard Area Delineation for Ralston Creek and Leyden Creek

SECTION 4.0 - HYDRAULIC ANALYSIS ................................................................................10

4.1 Introduction...... ..... ...................................... ........ ......... .............. ..........'''''''' 10

4.2 Hydrology and Hydraulics........................................................................... 10

4.3 Methodology......... ........................................ ...... ....... ................ .......... ........ 10

4.4 Floodplain Delineation ................................................................................ 10