PART IV of Attachment A INTERIOR DRAINAGE HYDROLOGY PART IV – INTERIOR DRAINAGE HYDROLOGY 1.0 Introduction ............................................................................................................................... 7 1.1 Study Area ....................................................................................................................... 7 1.2 Methodology .................................................................................................................... 7 1.3 Concurrent Flow Between Truckee River and Tributaries .............................................. 8 1.3.1 Interior Drainage Areas Behind Levees or Floodwalls ........................................ 8 1.3.2 North Truckee Drain Channel .............................................................................. 8 1.3.3 Steamboat Creek Channel .................................................................................... 9 1.3.4 Town of Lockwood and Long Valley Creek Channel ......................................... 9 1.3.5 Justification for Assumptions ..............................................................................10 1.4 References and Reports ....................................................................................................10 2.0 North Truckee Drain ................................................................................................................13 2.1 Study Area .......................................................................................................................13 2.2 Historical Floods ..............................................................................................................14 2.3 HEC-1 Models .................................................................................................................15 2.4 Flood Control Development ............................................................................................16 2.5 Runoff Model Development ............................................................................................16 2.5.1 Subbasin Delineation ...........................................................................................16 2.5.2 General Rainflood Storm Centered at Spanish Springs Dam ..............................16 a. 72-Hour General Rainflood ...........................................................................17 b. Depth-Area Reduction Factors .....................................................................23 c. Storm Centerings ...........................................................................................25 d. Rain-on-Snow ...............................................................................................25 2.5.3 Soil Loss Parameters ............................................................................................26 a. Soil type, Land Use, and Cover ....................................................................26 b. Green & Ampt Loss Parameters ...................................................................26 2.5.4 Hydrograph Development ....................................................................................28 2.5.5 Routing Parameters ..............................................................................................29 2.5.6 Special Facilities and Model Features .................................................................29 a. Diversions and Flow Splits ...........................................................................29 b. Detention Basins ...........................................................................................29 2.5.7 Model Verification ...............................................................................................30 2.5.8 Model Runs ..........................................................................................................30 2.6 Summary of Results .........................................................................................................32 2.7 Hydrology for Areas Behind Levees ...............................................................................32 2.7.1 3-Hour Cloudburst for Subbasins 404, 405, 410, 420, and 425...........................32 2.7.2 General Rain ........................................................................................................33 2.7.3 Depth-Area Reduction for Both Cloudburst and General Rain Storms ...............34 2.7.4 Results ..................................................................................................................34 3.0 Steamboat Creek ........................................................................................................................37 3.1 Study Area .......................................................................................................................37 3.2 Historical Floods ..............................................................................................................37 3.3 HEC-1 Models .................................................................................................................38 3.4 Subbasin Delineation .......................................................................................................38 3.5 General Rainflood ............................................................................................................38 3.6 Depth-Area Reduction Factors ........................................................................................39 2 3.7 Storm Centerings .............................................................................................................40 3.8 Snowmelt Analysis ..........................................................................................................41 3.9 Soil Loss and Land Use Parameters .................................................................................44 3.9.1 Soil Type, Land Use, and Cover ..........................................................................44 3.9.2 Green & Ampt Loss Parameters ..........................................................................45 3.10 Hydrograph Development ..............................................................................................46 3.11 Routing Parameters ........................................................................................................47 3.12 Model Verification .........................................................................................................48 3.13 Summary of Results .......................................................................................................50 4.0 Probable Maximum Flood for Huffaker Dam ........................................................................55 4.1 Introduction ......................................................................................................................55 4.2 Probable Maximum Precipitation (PMP) .........................................................................55 4.3 Snowmelt Contribution ....................................................................................................57 4.4 Washoe Lake Basin HEC-1 Model ..................................................................................58 4.5 Huffaker Hills HEC-1 Model...........................................................................................58 5.0 Hidden Valley Interior Drainage ..............................................................................................60 5.1 Introduction ......................................................................................................................60 5.2 General Rain Design Storm .............................................................................................60 5.3 HMS Model Components ................................................................................................61 5.4 Cloudburst Design Storm .................................................................................................61 6.0 South Side Meadows Reach near Airport Interior Drainage ................................................63 6.1 Introduction ......................................................................................................................63 6.2 Cloudburst Design Storm .................................................................................................63 6.3 General Rain Design Storm .............................................................................................63 6.4 HEC-1 Model ...................................................................................................................63 7.0 Interior Drainage behind Huffaker Dam ................................................................................65 7.1 Introduction ......................................................................................................................65 7.2 Cloudburst over Whites and Thomas Creeks...................................................................65 7.3 Cloudburst over Subbasins: 1301, 1306, and 1305 .........................................................67 7.4 General Rain for Interior Drainage behind Huffaker Dam ..............................................67 8.0 South Side of Downtown Reno .................................................................................................72 8.1 Introduction ......................................................................................................................72 8.2 Floodwall Upstream of Booth Street ...............................................................................72