Long Valley Creek:Long Valley Creek:A Rainfall-Runoff Modeling A Rainfall-Runoff Modeling

StoryStory

Rob ThompsonRob ThompsonHydrologistHydrologist

U.S. Army Corps of EngineersU.S. Army Corps of EngineersSacramento DistrictSacramento District

Robert.P.Thompson@usace.army.milRobert.P.Thompson@usace.army.mil

Reno/Truckee Reno/Truckee Meadows Flood Meadows Flood Control ProjectControl Project

Long Valley Long Valley CreekCreek

WatershedWatershed

Truckee Meadows 1997Truckee Meadows 1997Truckee Meadows 1997Truckee Meadows 1997

Long Valley Creek Model Long Valley Creek Model MethodologyMethodology

Feasibility studyFeasibility study Available data: one USGS peak flow gage and a Available data: one USGS peak flow gage and a

nearby rain gage.nearby rain gage. Gage: limited period of recordGage: limited period of record Correlated 2-day precipitationCorrelated 2-day precipitation to peak flow to extend recordto peak flow to extend record

Rainfall-Runoff ModelRainfall-Runoff Model Parameters physically basedParameters physically based

Gathered from maps, GIS, Gathered from maps, GIS, soil surveys, previous studiessoil surveys, previous studies

Model (loss rates) calibratedModel (loss rates) calibrated to frequency curveto frequency curve

HEC-1 vs HEC-HMSHEC-1 vs HEC-HMS

Rainfall-Runoff ModelingRainfall-Runoff Modeling

1.1. Characterize WatershedCharacterize Watershed

2.2. Develop PrecipitationDevelop Precipitation

3.3. Account for LossesAccount for Losses

4.4. Transform to Runoff HydrographTransform to Runoff Hydrograph

5.5. Route Hydrographs through the Route Hydrographs through the WatershedWatershed

6.6. Combine HydrographsCombine Hydrographs

The ProcessThe Process

Basin CharacterizationBasin Characterization

GEO-HMSGEO-HMS 11 Subbasins11 Subbasins Geometry:Geometry:

CentroidCentroid Centroidal Flow Centroidal Flow

PathPath Longest Flow Longest Flow

PathPath SlopeSlope Basin AreaBasin Area

Long Valley Creek, NVLong Valley Creek, NV

Design StormsDesign Storms

NOAA 14 precipitation frequency dataNOAA 14 precipitation frequency data 5- through 500-year events (7 5- through 500-year events (7

Frequencies)Frequencies) Storm centering to maximize peak Storm centering to maximize peak

runoffrunoff Areal Reduction FactorsAreal Reduction Factors Pattern Hyetograph -- Reno January Pattern Hyetograph -- Reno January

1963 Storm1963 Storm Balanced to 1, 3, 6, 12, 24 hour depthsBalanced to 1, 3, 6, 12, 24 hour depths

NOAA 14NOAA 14http://hdsc.nws.noaa.gov/hdsc/pfds/index.htmlhttp://hdsc.nws.noaa.gov/hdsc/pfds/index.html

Depth Area Reduction Depth Area Reduction FactorsFactors

12-Hour DARF = 0.01*(100-7.0*Area0.46)

24-Hour Pattern (Reno Jan 1963)

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (hrs)

Rain

fall (

in)

24-Hour Balanced 100-Year Storm

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (hrs)

Rain

fall

(in

)Peak 1 Hour

Peak 1 Hour

Peak 3 Hour

Peak 3 Hour

Peak 6 Hour

Peak 6 Hour

Loss RatesLoss Rates Initial and ConstantInitial and Constant

Initial Initial Initial losses set to 0Initial losses set to 0

ConstantConstant NRCS Soil Survey NRCS Soil Survey

DataData Long Valley Creek Long Valley Creek

> 75% D Type Soils > 75% D Type Soils Calibrated to Freq. Calibrated to Freq.

CurveCurve Percent ImperviousPercent Impervious

5%5%

Used LA Unit Hydrograph Procedure with Used LA Unit Hydrograph Procedure with S-graph from Truckee Meadows S-graph from Truckee Meadows

Computed lag from basin geometryComputed lag from basin geometry

User Generated Unit User Generated Unit HydrographsHydrographs

LL = Length of Longest = Length of Longest Stream Stream CourseCourseLcaLca = Centroidal Stream = Centroidal Stream LengthLengthSS = Slope ( = Slope (ΔΔElevation/L)Elevation/L)nn = Basin “n” – watershed = Basin “n” – watershed roughness roughness factorfactor

Lag = 24n{[(L x Lag = 24n{[(L x Lca)/(S^.5)]^.38}Lca)/(S^.5)]^.38}

RoutingRouting&&

CombininCombiningg

Muskingum Routing

Routing Time (K)Stream Velocity

Muskingum XVaries from 0 to 0.5Slope, Roughness

K < 1 hourX = 0.35

CalibrationCalibration

Loss rates adjusted for each event to Loss rates adjusted for each event to match frequency curvematch frequency curve

Larger event = lower loss ratesLarger event = lower loss rates

EventConstant Loss

Rate

10 year 0.16

50 year 0.13

100 year 0.10

200 year 0.08

500 year 0.04

End ResultsEnd Results

HydrographsHydrographs

FloodplainFloodplain

Results—Final Results—Final HydrographsHydrographs