StreamStats Web StreamStats Web ApplicationApplication

streamstats.usgs.govstreamstats.usgs.govAudrey Ishii, P.E.

Illinois Water Science Center

Overview—Streamflow Statistics

• What—Estimate of streamflow under some condition, such as the 100-year flood flow, flow durations, etc.

• Used in engineering design flows for bridges, culverts, mapping floodplains, setting water allocations, determining allowable waste discharges.

• How Computed—At stream gages--statistical analysis of historic flows, the flood-frequency or flow duration curveUngaged sites: Regression equations relating the characteristics of the curve to basin characteristics.

Q100 = a(TDA)b(MCS)c(PermAvg)d(Rf)

Selected discharge gages with more than 25 years of record for analysis.

Streamflow gaging stations are not distributed evenly.The density impacts the quality of regional analyses.

Percentage changes in the 100-year peak flow estimate between 1987 and 2004

1Max. = 35Avg. = 6

Max. = 50Avg. = 27

Max. = 29Avg. = 4

Max. = 81Avg. = 9

Max. = 24Avg. = 7

Max. = 95Avg. = 15

Max. = - 2Avg. = - 8

Traditional Methods for Measuring Basin Characteristics

• Very labor intensive and costly• Not completely reproducible• Error-prone• Often not documented well in reports• Users need source materials and expertise• Some BC not easily reproduced by GIS methods

GIS Methods for Basin Characteristics

• Several custom software packages developed, GIS Weasel, BasinSoft, BASINS, WMS, mostly developed for watershed modeling, often ESRI.

• Needed GIS datasets not always readily available • No documented national standard methods• Several methods used for some characteristics• Users need source data and expertise• Often not documented well in reports• Some measurements are scale-dependent

StreamStats GIS computations

• Create hydro networks of rivers and streams

• Process DEM and stream network for watershed analysis

• Delineate drainage basins and measure basin characteristics

• Represent channel shape using three-dimensional models

• Connect geospatial features to time series measurements recorded at gaging sites

• Runs within ESRI Arc 8/9 software• Public domain utilities developed

jointly by U. Texas at Austin and ESRI

StreamStats Web Application

• Provides published streamflow statistics and basin characteristics for gages

• Computes basin characteristics for ungaged sites

• Provides regression-based estimates of streamflow statistics for ungaged sites

User InterfaceArcIMS

Streamflow Statistics Database

NSS Calculation

Program

GIS DatabaseArcHydro

At astreamgage

At an ungaged location

StreamStats Benefits

• Cost—Time to delineate and compute basin characteristics reduced from hours to minutes

• Accuracy—As good or better than manual methods• Consistency—Important for statistical validity• Accessibility—User does not need GIS expertise or

software

National StreamStats Status

• 14 states up and running• National gages web site• 14 additional states underway• Data upgrades on 3

states (PA, ID, WA)• Each state is developed

(and funded) separately

http://streamstats.usgs.gov

•Read the user guidance provided in the links at the left of the main page.

•Access the Illinois application from the main StreamStats page at http://streamstats.usgs.gov

Obtaining the basin characteristics and flood quantiles—select the site using the latititude and longitude Zoom To

Delineate the watershed using the BasinDelineation tool

Generate a streamflow statistics report at any site.

Evaluation of Illinois StreamStats

• Basin characteristics at 283 USGS rural gaging stations

• Sensitivity of basin characteristics to estimated flood quantiles

• Flood quantiles at 169 USGS rural gaging stations (random sampling)

• Reliability testing

Basin Characteristics Differencesin the Illinois Studies

• Digitized watersheds• 30-m DEM• NHD (1:100K)• Manually extended main

channel to saddle point for slope computation

• Automated basin delineation• 30-m DEM (newer)• Hydro-corrected NHD (1:100K)• Longest flow path method to

determine main channel and intersection point with upper boundary

Published (BasinSoft) StreamStats

Evaluation of Basin CharacteristicsDRAINAGE AREA

n=283

0

2000

4000

6000

8000

10000

0 2000 4000 6000 8000 10000

STREAMSTATS

BA

SIN

SOFT

MEAN CHANNEL SLOPE CORRECTION LOG EQUATIONn=283

y = 1.0767x0.9486

R2 = 0.9529

0

1

10

100

1000

0 1 10 100 1000

StreamStats_SL

Bas

inSo

ft_SL

0.01

0.10

1.00

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0.10 1.00 10.00 100.00 1000.00

StreamStats_SL

Stre

amSt

ats_

DA

StreamStats values of drainage area, mean channel slope, basin length, average permeability, percent open water were compared with the published values used in the last flood frequency update. The results for drainage area and mean channel slope are shown on the left. The relation between drainage area and slope is shown below.

Distribution of relative differences between StreamStats (SS) and the published values (BS) for DA

ERROR INTERVAL (BS-SS)/BS-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6

NU

MB

ER

OF

EV

EN

TS

0

20

40

60

80

100

120

140

Mean = 0.0, STD = 0.10The range of ± 1 STD is shown n=283

ERROR INTERVAL, (BS-SS)/BS-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

PE

RC

EN

TAG

E E

RR

OR

IN F

LOO

D Q

UA

NTI

LE

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

Sensitivity of flood quantiles to differences in DA: Errors associated with one standard deviation

-7.3%

7.5%

1 STD

Errors are for Q100 from Regions 1,3,5

Summary of Basin Characteristics Evaluation

• Automatically delineated drainage area generally agrees well with manually delineated (differences are not statistically significant).

• Discrepancy appears to occur more frequently in small watersheds (DA < 0.5 mi2).

• It appears that controls on flow such as roads and culverts has a larger effect for small watersheds. Judgment (the EditBasin tool) can be used to ensure the correct delineation.

• Slope definition differs, but sample differences by region were not significant after adjustment.

Q100 Estimates

0

10000

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90000

0 10000 20000 30000 40000 50000 60000 70000 80000 90000

StreamStats

Publ

ishe

d

100-year peak estimates using BasinSoft and manual drainage basin delineation against StreamStats for all regions, n = 164, without manual corrections or user judgment.

Arithmetic Scale

The differences are not statistically significant by paired t-test and Wilcoxon Signed Rank test (p-value < 0.05) whether by region or total, except for Region 1. No region had statistically significant differences in SL, DA, or any other basin characteristic.

PROVISIONAL RESULTPROVISIONAL RESULT

Reliability Testing

• Eight new users tested StreamStats at 28 typical structure sites over state (8 repeated values).

• One structure site was eliminated from the study because of identification uncertainty.

• Five structure sites were misidentified or misread by single testers, so those results were omitted, leaving 7 repeated tests for 5 sites, 8 repeated tests for 22 sites.

• The average absolute maximum deviation from the mode of responses was 1.34 percent for the 27 structures tested by 7-8 users.

• Conclusion: Extremely reliable results provided that the site is correctly identified.

Average absolute maximum deviation from the mode = 1.31 percent

Reliability Testing

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Q100 = 1760Q100 = 6110

Q5 Estimates--Repeats and OptionalN = 30

1000 2000 3000 4000 5000 6000 7000

StreamStats

OPTIONAL

OPTIONAL

REPEATED

Comparison of IDOT manual determinations with StreamStats.

New IDOT Structure Information Management (SIMS) Layer

• As a result of the reliability test results, a new layer was added to the application to provide identification for the IDOT structures.

• Other layers can be added upon request.

• The next slide illustrates the features of the new layer.

Use the i button to get the structure number.

Check the IDOT structure layer and refresh

StreamStats Enhancements

• Porting to ArcGIS Server/Web Services– Batch jobs, multi-user, transparent remote

access, stability• NHD Navigation/Reach indexing

– Drainage-area ratio for ungaged sites– Stream tracing for dams, point Q’s, etc.

• Weighted estimates for ungaged basins that cross state lines

• IDOT Structure Inventory Management System (SIMS) shapefile

Future Illinois refinement:1:24K NHD, 10-m DEM

24K (Hi-res) NHD recently completed, 10-m DEM is being completed now.hio has already incorporated this data into their StreamStats application.

Estimate of QTs in Ungaged AreasEstimate of QTs in Ungaged Areas

Design storms

Frequency analysis

Event model

Regionalequations

streamstats.usgs.gov

Synthetic frequency curves Continuous

simulation model

Event model