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TABLE OF CONTENTS Pa~e N2 Letter of Transmittal Table of Contents. . _ _ _ _ _ . _ _ _ . . . . . . . _ . . . _ _ _ _ . _ . . . . _ . . . _ _ _ _ _ _ . . . . _ _ . _ _ _ _ . . _ _ _ _ _ _ _ . _ _ _ . _ . _ _ . . . . _ _ _ _ i List of Tables _....... _ _ _ _ _ _ _ _ . _ . . . . . . . . . . . . . . . . . _ _ . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . _ . . . i List of Figures . _ _ _ _ __ _ __ . __ . . . . __ _ _ . . __ . _ . . . _ __ _ _ __ -' _ _ __ -' __ _ _ __ _ . .. i List of Appendices .... _ _ _ _ _ _ _ _ . _ _ _ . . _ . . . . . . _ _ . . . . . _ . _ . _ _ _ _ . . . . . . _ . _ . : : : : _ : : : : : : : : : : : : : : : : i List of Drawings _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ . . . . _ _ _ _ _ . _ . _ . . . . . _ . . _ _ _ . _ . _ . . . _ . _ _ . . ., .. .' \-\- .... . ......... I. Introduction . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . . . _ . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-I ~: ~~;~:~ ~~d-S~~~~: ::: :: : :: :: : :'_: : : : : : : :::::::'_: -. : -_::: -_ : -_ : -.:: : : : -_ : : : ::: : -_: -_:: -. : -- -- ~~~ C. Mapping and Surveys _ _ _ . _ _ . . _ _ _ . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . _ . . . _ . . . . . . . . . . . . . . . I-I D_ Information Procurement. . . . . . . . . . . . _ _ _ . _ _ _ _ . _ _ _ _ _ _ _ _ _ _ . . . _ . _ . _ _ _ . . _ _ _ _ _ . _ _ _ _ _ _ _ _ _ I-I E_ Analysis and Design Criteria _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ . _ . 1-3 F_ Project Advisory Committee _ _ _ _ _ . . _ . _ . . . _ _ . _ _ . . . . . . . . . . _ . . . . . . . . . . _ . . _ _ _ _ . . _ _ . . . . . 1-3 II. Study Area Description. . _ _ _ . . _ _ . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ II-I III. Hydrologic Analysis .. _ . . _ . . . . _ . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ III-I A. General _ . _ _ _ _ . _, _ _. _ _ _ _ _ _ _. _ _. _ _ _ _ _ _ . _ .. _ . _ _ .. . .. _ _ _ _ _ _ . . _. _ _ _ _ _ _ . _ _ _ _ . . . _ _ . . . III-I B- Design Rainfall . _ . _ . . . . . _ . . . . . . . . . . . _ _ . . . . . _ _ . _ _ . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . III-I C Colorado Urban Hydrograph Procedure Parameters _ _ . _ _ _ _ _ _ _ _ _ _ _ . _ _ . _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ III-I D. Storm Water Management Model _. _ _ _ . _ _ . . . . . . . . . . . . . _ . . . _ . . . _ _ _ _ _ _ _ _ . _ . . _ . . . . . . . III-25 E- Modeling Results. . . . . . . . . . . . . . . . . . . _ _ _ _ _ . . . _ . . _ _ _ _ . _ . _ _ _ _ . . . _ _ . . . . _ . _ . _ _ _ _ _ _ _ _ III-25 IV_ Hydraulic Analysis _ _ _ _ . _ IV-I IV-I IV-I IV-2 IV-2 IV-2 ............................................................. A. General . . . . . . . . . _ . . . . _ _ . . . . . . _ . . . . _ _ . _ _ _ _ _ _ _ . - - - - - - - - - - - - - - - B_ Hydraulic Parameters _ . _ _ _ _ _ . _ _ _ _ _ _ _ _ . . . . . . . . . . . . . . . . . . . - . . . . . . : : : : : : : : : : : : : : : : : C Analyzed Flood Frequencies - - - . . . . . . . . . . . _ . _ _ . _ . - - - - - . . . - . - . . . - . . . . . - . - . . . . - . . . . D_ Water Surface Profile Determination '" E. Shallow Floodingllneffective Flow Areas : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : V. Flood Hazard Area Delineation _ _ . . _ _ _ . _ _ . _ _ _ . _ . . . . . . _ . . . . . _ . _ _ _ _ _ . _ _ _ _ . _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ V-I A. General _ _ _ _ _ _ _ _ _. _. _ _. . . _ _. _ .. . . . ..... . . . ..... _ . .. .. . . . .. . . . ... ., . .. . .. .. . .. .. V-I B- Floodplain/Floodway . . .. . .. .. . . _ . _. . . _ . _ _ _ _ _ _ _. _ _ _ _ _ _ _ _ _. _ _ _ _ _ . . _ _ . . . _ ..... . . _ _ _ V-I C Comparison with 1993 Flood Insurance Study ............. _ _ _ _ . . _ _ _ _ . . _ . _ _ _ _ . _ _ _ _ _ _ _ _ V-I D. Description of Channel Reaches and Floodplains. _ _ _ . _ _ . . . _ _ . . _ _ . . . . . . . . . . . . _ _ _ . . . _ .. V -21 References Appendices Drawings Table III-I Table III-2 Table III-3 Table III-4 Table III-5 Table III-6 Table III-7 Table III-8 Table III-9 Table III-I 0 Table III-II Table III-I 2 Table III-I 3 Table III-14 Table III-I 5 Table III-16 Table III-I 7 Table III-I 8 Table V-I LIST OF TABLES Pa~e N2 Douglas County Zone 1-2 Hour Unadjusted Rainfall Distribution. . . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ . . . . - III-9 Douglas County Zone 1-3 Hour Adjusted Rainfall Distribution _ _ _ . _ . . _ . . . . _ _ . . . _ _ _ _ _ _ _ _ . . III-9 Douglas County Zone 1-6 Hour Area Adjusted Rainfall Distribution _ _ . . . _ _ _ . . _ _ _ . . . . . . ., III-I 0 Douglas County Zone II-2 Hour Unadjusted Rainfall Distribution. . . . . _ _ . _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ III-II Douglas County Zone II-3 Adjusted Rainfall Distribution _ _ _ _ _ _ _ _ _ _ . _ . _ _ _ . . . _ _ . . . . . . . . . III-II Douglas County Zone II-6 Hour Area Adjusted Rainfall Distribution. _ . _. . . _ _ _. _ _ _ _ _ _ _ _ _ III-12 CUHP Sub-Watershed Parameters for West Section of Study Area _ _ _ . . . _ _ _ . . .. _. III-13 to III-I 6 CUHP Sub-Watershed Parameters for Southeast Section of Study Area _ _ _ _ _ _ _ _ _ _ _ III-I 7 to III-19 CUHP Sub-Watershed Parameters for East Section of Study Area '" _ _ . . . . . . . . .. III-20 to III-23 CUHP Sub-Watershed Parameters for Off-Site Area _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.... _ _ _ _.... _. III-24 Infiltration Parameters for Off-Site Soil _ _ _ _ _ . _ . _ . . . . _ _ . . . _ . _ _ _ _ . _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ III-32 SWMM Parameters for West Section of Study Area . _. _ .. _ _ . .. _ . . . .. ., . _ . . ... III-33 to III-35 SWMM Parameters for Southeast Section of Study Area _ _ _ _ _ . . _ . _ _ _ . . _ _ . _ _ . _ _ III-36 to III-37 SWMM Parameters for East Section of Study Area _ _ . _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ III-38 to III-40 SWMM Parameters for Off-Site Area. . . _ _ . . . . . . . _ _ _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-41 Peak Flows in the West Section of the Study Area (Including Off-Site Area) _ _ _ _ _ _ _ III-52 to III-57 Peak Flows in the Southeast Section of the Study Area (Including Off-Site Area) ... III-58 to III-63 Peak Flows in the East Section of the Study Area. _ _ _ _ _ _ _ _ . _ _ _ . _ . _ _ _ _ _ _ _ . . _ _ _ _ III-64 to III-70 Floodplain and Floodway Data. . ... . _ _ _.... _ _ _ _ _. . _ _ _ . _ _ _ _ _ ,... __ _ _ _ .. _ __.. V-2 to V-20 LIST OF FIGURES Figure I-I Figure III-I to III-6 Figure III-7 Figure III-8 Figure III-9 Figure III-I 0 Figure III-II Figure III-I 2 Figure III-13 Figure III-I 4 to III 19 Figure III-20 Figure III-21 Figure III-22 Figure III-23 Study Area _........... _ _ . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ . . _ _ _ . . . . 1-2 Sub-Watershed Boundary/Study Area................... _ _..:::::::' rri~2~~iII-7 Sub-Watershed Boundary/Off-Site Area with Rainfall Zones _ _ _. _ _ _ _ _ _ _ _ _ _ _ _ . _ Ill-8 Existing Watershed Imperviousness/Study Area _ . . _ _ . . . . . _ . . . . . . . . . . . . . . . . . Ill-26 Future Watershed Imperviousness/Study Area .......... _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ III-27 Existing Watershed Imperviousness/Off-Site Area _ _ . . _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ IlI-28 Future Watershed Imperviousness/Off-Site Area .. _ _ _ , . . . _ . . _ . . . . . . . . . . . . . . Ill-29 Soils Boundary/Study Area _ _ _ _ _ _ _ _ _ _ _ _ _ _ . . . . . _ _ . . . . . . _ . . _ _ _ _ _ _ _ _ _ _ _ _ . _ Ill-30 Soils Boundary/Off-Site Area _ _ . _ . _ . . . . . . . . . _ _ . . . _ . . _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ . . _ III-31 SWMM Routing Elements/Study Area . _ _ _ _ _ _ . . . _ . _ . . . . _ . . . . . . . .. III-42 to III-47 SWMM Routing Elements/Off-Site Area ............ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ III-48 Unit Runoff in West Section of Study Area for all Sub-Watersheds. . . _ _ . . . . . _ . . III-49 Unit Runoff in Southeast Section of Study Area for all Sub-Watersheds _.. _ _ _ _. _ III-50 Unit Runoff in East Section of Study Area for All Sub-Watersheds _. _ _ _ _ _...... III-51 Appendix A LIST OF APPENDICES Peak Flow Diagrams and Typical Hydrographs