Central Valley hydrology study November 29, 2015 Prepared for California Department of Water Resources Letter of agreement #4600007762 Prepared by US Army Corps of Engineers Sacramento District and David Ford Consulting Engineers, Inc. Contents Expectations of use .............................................................................. 7 Purpose of the hydrology .................................................................... 7 Responsibility of users ....................................................................... 7 Basic assumptions and limitations ........................................................ 7 Executive summary ............................................................................ 10 Situation ........................................................................................ 10 Analysis overview ............................................................................ 10 Requirements .............................................................................. 10 Procedure overview ...................................................................... 11 Analysis review and oversight ........................................................... 12 Results .......................................................................................... 12 Introduction ...................................................................................... 13 Authority ........................................................................................ 13 Watershed description ...................................................................... 13 Sacramento and San Joaquin river basin flood control system ................ 16 Motivation of current DWR studies of the watershed ............................. 17 Hydrology study .............................................................................. 19 Study requirements ......................................................................... 20 Potential effects of climate change on study results .............................. 20 Purpose of documentation ................................................................ 20 Approval and certification ................................................................. 20 Relevant documents ........................................................................ 20 Comparison to previous watershed study ............................................... 21 Watershed description......................................................................... 27 Sacramento River basin ................................................................... 27 Basin characteristics ..................................................................... 27 Hydrography ............................................................................... 28 Topography ................................................................................. 29 Soils 29 Vegetation .................................................................................. 29 Climate ....................................................................................... 29 Temperature ............................................................................... 30 Precipitation ................................................................................ 30 Snowpack ................................................................................... 31 San Joaquin River basin ................................................................... 31 Basin characteristics ..................................................................... 31 Hydrography ............................................................................... 32 Topography ................................................................................. 32 Soils 33 Vegetation .................................................................................. 33 Climate ....................................................................................... 33 Temperatures .............................................................................. 33 Precipitation ................................................................................ 34 Snowpack ................................................................................... 35 Analysis procedure ............................................................................. 36 3 Overview of procedure ..................................................................... 36 Mixed population analysis and integration into the CVHS ....................... 39 Mixed population analysis .............................................................. 39 Separation of events to create the time series .................................. 40 Regional skew and its use in CVHS ..................................................... 40 Term “unregulated flow” and its use in CVHS ...................................... 45 Study products and applications ........................................................... 48 Study products ............................................................................... 48 First application regulated condition products ...................................... 48 Application of study products ............................................................ 49 Unregulated flow time series development ............................................. 54 Estimate daily reservoir inflow ........................................................... 54 Situation ..................................................................................... 54 Pertinent guidance and discussion .................................................. 54 Study procedure .......................................................................... 57 Estimation of ungaged local flows ...................................................... 57 Situation ..................................................................................... 57 Pertinent guidance and discussion .................................................. 58 Study procedure .......................................................................... 59 Application and distribution of local flow ............................................. 59 Situation ..................................................................................... 59 Pertinent guidance and discussion .................................................. 59 Study procedure .......................................................................... 60 Approach for extending data or filling in gaps ...................................... 60 Situation ..................................................................................... 60 Pertinent guidance and discussion .................................................. 61 Description of methods to support flow-frequency analysis ................. 61 Methods to support assessing the effects of regulation....................... 62 Study procedure .......................................................................... 62 Smooth unregulated flow time series.................................................. 62 Situation ..................................................................................... 62 Pertinent guidance and discussion .................................................. 62 Study procedure .......................................................................... 63 Procedures for routing unregulated flows through the system ................ 63 Situation ..................................................................................... 63 Pertinent guidance and discussion .................................................. 63 Study procedure .......................................................................... 65 Unregulated frequency analysis ............................................................ 66 Separation of seasonal data .............................................................. 68 Situation ..................................................................................... 68 Pertinent guidance and discussion .................................................. 68 Study procedure .......................................................................... 69 Identify annual maximum series ........................................................ 69 Situation ..................................................................................... 69 Pertinent guidance and discussion .................................................. 69 Study procedure ............................................................................. 70 Calculate regional skew values .......................................................... 70 Situation ..................................................................................... 70 4 Pertinent guidance and discussion .................................................. 70 Study procedure .......................................................................... 70 Fit frequency curves ........................................................................ 71 Situation ..................................................................................... 71 Pertinent guidance and discussion .................................................. 71 Study procedure .......................................................................... 71 Review and adopt curves .................................................................. 72 Situation ..................................................................................... 72 Pertinent guidance and discussion .................................................