Alameda County Hydrology & Hydraulics Manual

Alameda County Hydrology & Hydraulics Manual Rohin Saleh, MS. PE. Supervising Civil Engineer, ACFCD

Alameda County Flood Control District Established in 1949

Use the updated criteria for: Any project that drains to a District facility or is subject to District approval Modifying existing flood control infrastructure or designing new District facilities Drainage Studies and new developments within District watersheds

New H&H is: Comprehensive Guidelines for hydrology and hydraulics Regionally Calibrated Use of local and regional data Adaptable To areas with little or no stream flow data

From rainfall to runoff Rainfall Event Answers basic challenge in hydrologic engineering Design discharges and FEMA floodplain maps are all based on runoff frequencies Runoff Soil AMC Infiltration Rate Impervious Area Other Factors

Reliable Source for Design and Flood Plain Evaluations Unknown Level of Reliability Most available methodologies are based on hydrology text books or the “shopping card versions” Know Level of Reliability based on measured data Alameda County methodology links rainfall statistics to runoff statistics

Effects of commonly estimated Kinematic Wave Parameter Percent Difference from Measured Peaks

Why we need better estimates of Runoff Statistic : If you can design a drainage pipe with a velocity of 12 FPS you will need: 12” RCP for every 10 CFS 18” RCP for every 20 CFS 24” RCP for every 40 CFS 48” RCP for every 150 CFS

Why we need better estimates of Runoff Statistic : Substantial impact to project cost particularly if its used for improvement of existing facilities We need to distinguish between evaluation and improvement of an existing facility vs. adding a totally new drainage facility for the first time

Why we need better estimates of Runoff Statistic : Flood Plain impacts (Unnecessary Flood Insurance) Increase liability if you are evaluating an existing facility Increase risk by wasting public fund in a wrong location and ruining out of money where you truly need projects. Wrong runoff estimates can be obvious

Research & Development for Production of the H&H Manual

Rainfall Frequency for MAP “N” & Duration “X” Discharge “Q” at the Point of Interest Rainfall Depth Discharge (cfs) (inches) 1 10 100 1 10 100

Infiltration Rate Infiltration Rate (in/hr) Initial Infiltration Rate Uniform Infiltration Rate Time

Land Use

Unit Hydrograph Parameters Time to Peak (lag) U.H. for Steep Catchment Q/Qp U.H. for Average Catchment U.H. for Flat Catchment Time

Design Storm 1.80 Hourly Precipitation (inches) 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 2 3 4 5 6 7 8 9 10 11 12 13 14 Elapsed Time (hours) 15 16 17 18 19 20 21 22 23 24

From Rainfall Statistic to Runoff Statistic Infiltration: Initial (AMC): Statistical Uniform: Physical Land Use & Effective Impervious Areas: Physical Hydrologic Soil Group: Physical Unit Hydrograph or Kinematic Wave: Physical Design Storm: Statistical

Active rain gauges & flow monitoring stations 60 Stream or flow stations 50 Recording rain gauge stations 150 Daily rainfall observers

1994: Initiation of calibrated hydrology models and methods

Comprehensive studies of entire network Open channels Closed conduits Floodplains

Floodplains Accurate representation of floodplain boundaries Impact to the community

Access to quality data sets High quality data from select small urban catchments in Alameda County and City of San Jose

Detailed land use data Building rooftops Driveways & sidewalks Roads Yards & greenways

Detailed land use data

Calculation of Effective Impervious Area Significant impact on accuracy of runoff calculations Guidance on managing new low-impact development

Soils NRCS data Custom soil testing Reclassification of hydrologic soil groups

Time of concentration and basin lag

Storm events Production of rainfall spatial distributions and maps for hundreds of calibration events

Storm events calibration 20 18 45 20 7 40 18 16 16 35 6 14 14 30 5 8 12 4 3 25 F low (cf s) 10 F low (cf s) F low (cf s) F low (cf s) 12 20 10 8 15 6 6 2 10 4 4 2 0 15:00 16:00 17:00 16Dec1914 CAL 01 RC OBSERVED FLOW 18:00 19:00 20:00 21:00 22:00 23:00 CAL01 RC CALC FLOW 1 5 0 22:00 00:00 02:00 14Dec1914 CAL 01 RC OBSERVED FLOW 0 06:00 04:00 06:00 08:00 10:00 12:00 15Dec1914 2 12:00 11Dec1914 CAL01 RC OBS FLOW CAL01 RC CALC FLOW 35 09:00 15:00 18:00 21:00 00:00 03:00 06:00 12Dec1914 CAL01 RC CALC FLOW 0 12:00 13:00 14:00 31Mar1914 CAL01 RC OBS FLOW 12 15:00 16:00 17:00 18:00 19:00 20:00 CAL01 RC CALC FLOW 14 20 30 12 10 25 10 15 8 20 10 F low (cf s) 15 F low (cf s) 8 F low (cf s) F low (cf s) Large and small storm events used for calibrations of various parameters 8 6 6 4 10 4 5 2 5 0 00:00 0 03:00 CAL01 RC OBS FLOW 06:00 09:00 12:00 28Feb1914 CAL01 RC CALC FLOW 15:00 14:00 16:00 26Feb1914 CAL01 RC OBS FLOW 18:00 20:00 22:00 00:00 CAL01 RC CALC FLOW 02:00 27Feb1914 2 0 00:00 02:00 CAL01 RC OBS FLOW 04:00 06:00 08:00 CAL01 RC CALC FLOW 10:00 12:00 06Feb1914 0 13:00 13:30 14:00 20Nov1913 CAL01 RC OBS FLOW 14:30 15:00 15:30 16:00 CAL01 RC CALC FLOW 16:30 17:00

Data gathering & review Calculated, calibrated, land use variables

Model results: validation Review of model results for complex large watersheds with multiple stream gauges and long-term flow data

Alameda Creek at Niles (11179000) 100000 95% Low Discharge (CFS) Model results: statistical comparison Bull 17B 95% Up Model 10000 Discharge frequency analysis 1000 1 10 Return Period (YR) 100

Model results: validation Review of model results for complex large watersheds with multiple stream gauges and long-term flow data

Model results & validation Comparison of the model results with statistical gauge analysis (Log Pearson-Type III) where long period of record was available. Model result validation on consecutive gauges with long term data unaffected by man made operations

Arroyo las Positas near Livermore (11176145) 95% Low 100000 Bull 17B 95% Up Model Discharge (CFS) 10000 1000 100 1 10 Return Period (YR) 100

Arroyo Mocho near Livermore (11176000) 95% Low 100000 Bull 17B 95% Up Model Discharge (CFS) 10000 1000 100 1 10 Return Period (YR) 100

Arroyo Valle below Lang Canyon near Livermore (11176400) 95% Low 100000 Bull 17B 95% Up Model Discharge (CFS) 10000 1000 100 1 10 Return Period (YR) 100

Arroyo Hondo near San Jose (11173200) 95% Low Bull 17B 95% Up Model Discharge (CFS) 100000 10000 1000 1 10 Return Period (YR) 100

Arroyo de la Laguna at Verona (11176900) 95% Low 100,000 Bull 17B 95% Up Model Discharge (CFS) 10,000 1,000 100 1 10 Return Period (YR) 100

Alameda Creek at Niles (11179000) 95% Low Discharge (CFS) 100000 Bull 17B 95% Up Model 10000 1000 1 10 Return Period (YR) 100

Coyote Creek Upstream of Coyote Reservoir 95% Low Discharge (CFS) 100000 Bull 17B 95% Up Model 10000 1000 1 10 Return Period (YR) 100

Outcome with and without the calibrated model Improved floodplain accuracy Cost benefits BEFORE AFTER

Main Components of H&H Manual INSERT nice photo of Ala Co stream

Impervious percentage calibrated and more accurate

Clear definition of required levels of service and how to apply them

Refined hydraulic equations for junction losses

Refined synthetic hydrograph calculations

Detention pond criteria added

New mean annual precipitation map

New rainfall equations: intensity and depth

New runoff coefficient values per soil classification

6-hour and 24-hour design storm better defined

Tidal data based on latest FEMA studies

Available free-of-charge at: acfloodcontrol.org/hh-manual Questions: rohin@acpwa.org

Alameda County Hydrology & Hydraulics Manual Rohin Saleh, MS. PE. Supervising Civil Engineer, ACFCD. Alameda County . Guidelines for hydrology and hydraulics . Arroyo de la Laguna at Verona (11176900) 95% Low. Bull 17B. 95% Up. Model. 1000. 10000. 100000. 1. 10. 100.