ARIZONA DEPARTMENT OF WATER RESOURCES FLOOD MITIGATION SECTION State Standard For Hydrologic Modeling Guidelines Under the authority outlined in ARS 48-3605(A) the Director of the Arizona Department of Water Resources establishes the following standard for Hydrologic Modeling Guidelines in Arizona. State Standard for Hydrologic Modeling, or “guidelines for the experienced modeler”, has been developed to address hydrologic conditions for a variety of statewide watersheds. Included are problems and situations identified by the State Standard Work Group (SSWG) and floodplain managers. The intended audience is statewide; engineers, professionals and Floodplain Administrators. The following topics are included: • Hydrologic Model comparison and recommendation • Guidelines and parameters • Model application for specific situations, and associated hydrologic parameters • Precipitation values (NOAA 14) • Storm duration • Unique conditions, such as wildfire burn, overgrazing, logging, drought, rapid snowmelt, urbanization. The State Standard includes examples addressing the above key issues. This requirement is effective August, 2007. Copies of this State Standard and the State Standard Technical Supplement can be obtained by contacting the Department’s Water Engineering Section at (602) 771-8652. SS10-07 1 August 2007 TABLE OF CONTENTS 1.0 Introduction.......................................................................................................5 1.1 Purpose and Background .......................................................................5 1.2 General ...................................................................................................5 1.3 Overview of Standard.............................................................................6 2.0 Hydrologic Models............................................................................................7 2.1 General ...................................................................................................7 2.2 Model Selection......................................................................................7 2.2.1 Model Evaluation Criteria ............................................................7 Parameters..................................................................................7 2.2.2 Evaluated Models........................................................................8 2.2.3 Recommendation ......................................................................11 3.0 Modeling Process and Procedure.................................................................12 3.1 General ................................................................................................12 3.2 Project Description and Initialization .....................................................12 3.3 Precipitation Data..................................................................................13 3.3.1 General .....................................................................................13 3.3.2 Depth-Duration-Frequency Statistics........................................13 3.3.3 Depth-Area Reduction...............................................................14 3.3.4 Rainfall Distribution ...................................................................18 3.3.5 Procedures................................................................................18 3.4 Subbasin Data......................................................................................21 3.4.1 Prepare Watershed Map ...........................................................21 3.4.2 Rainfall Losses..........................................................................21 3.4.2.1 Evaporation and Interception......................................22 3.4.2.2 Depression Storage....................................................23 3.4.2.3 Infiltration During Initial Abstraction ............................24 3.4.2.4 Method for Rainfall Losses .........................................24 3.4.2.5 Impervious Area.........................................................28 3.4.2.6 General Considerations for Rainfall Losses ...............29 3.4.2.7 Procedures for Rainfall Losses...................................34 3.4.2.8 Applications and Limitations for Rainfall Losses ........35 3.4.3 Unit Hydrographs ......................................................................36 3.4.3.1 General.......................................................................36 3.4.3.2 Method for Unit Hydrographs .....................................36 3.4.3.3 Unit Hydrograph Duration...........................................39 3.4.3.4 Unit Hydrograph Procedure........................................42 3.4.3.5 Application and Limitations for Unit Hydrographs.......43 3.5 Channel Routing...................................................................................44 3.5.1 General .....................................................................................44 3.5.2 Methods for Channel Routing....................................................44 Modified Puls.............................................................................44 Kinematic Wave ........................................................................44 SS10-07 2 August 2007 TABLE OF CONTENTS Continued 3.5.3 General Considerations.............................................................45 Routing......................................................................................45 Kinematic Wave ........................................................................46 3.5.4 Procedures for Channel Routing...............................................47 3.5.5 Applications and Limitations for Channel Routing.....................48 3.6 Storage Routing....................................................................................49 3.7 Hydrograph Combinations....................................................................49 3.8 Diversions .............................................................................................50 4.0 Unique Watershed Conditions ......................................................................52 4.1 Transmission Losses............................................................................52 4.1.1 General .....................................................................................52 4.1.2 Procedure..................................................................................52 4.2 Wildfire Burn .........................................................................................54 4.2.1 Rainfall Losses..........................................................................56 4.3 Grazing .................................................................................................60 4.4 Logging .................................................................................................60 4.5 Drought .................................................................................................61 4.6 Rapid Snowmelt....................................................................................61 4.6.1 Background ...............................................................................61 4.6.2 Methodologies...........................................................................62 4.6.3 Guidelines .................................................................................63 Snowmelt-Runoff.......................................................................64 Snowmelt Coefficient.................................................................64 Base Temperature.....................................................................64 Air Temperature ........................................................................64 Snow Water Equivalent.............................................................65 Snowmelt Losses ......................................................................66 Rainfall-Runoff ..........................................................................66 4.6.4 Procedures................................................................................67 4.6.5 Applications and Limitations......................................................67 4.7 Urbanization..........................................................................................68 5.0 References ......................................................................................................69 SS10-07 3 August 2007 TABLE OF CONTENTS Continued List of Figures Figure 3.1 Depth-Area Relation Zones.......................................................15 Figure 3.2 Depth-Area Reduction Relation for Western Arizona................16 Figure 3.3 Depth-Area Reduction Relation for Eastern Arizona.................17 Figure 3.4 NOAA Atlas 14 Precipitation Frequency Data Server Input ......19 Figure 3.5 NOAA Atlas 14 Precipitation Frequency Data Server Output ...20 Figure 3.6 Rainfall Loss Process................................................................22 Figure 3.7 Composite Values of PSIF and DTHETA as a Function of XKSAT............................................................26 Figure 3.8 Effect of Vegetation Cover on Hydraulic Conductivity...............27 Figure 3.9 Status of Soil Surveys – Publication..........................................31 Figure 3.10 Status of Soil Survey – Digitizing ..............................................33 Figure 3.11 Synthetic Time-Area Relation....................................................41 Figure 3.12 Example Input Files...................................................................51