Estimating Daily Streamlow at Ungaged Sites in NH: A Modeling Update - - PowerPoint PPT Presentation

Estimating Daily Streamlow at Ungaged Sites in NH: A Modeling Update

Neil M. Fennessey HYSR/Hydrologic Services

HYSRConsult@gmail.com

NH Department of Environmental Services Concord, NH March 29, 2018

Estimating Daily Flows at Ungaged Sites

 NH DES needs to determine PISFs at ungaged

sites in presently and future designated rivers

 NHDES needs a reliable way to estimate daily

streamflow time series at these ungaged sites

 The QPPQ Transform method is one approach  Conceived and developed by Fennessey (1994)  Has been used in the northeast and central US,

Canada and South Africa

Other Ways to Estimate Daily Flows at Ungaged Sites: Pluses & Minuses

 Watershed Area Ratio (WAR) method  Very simple to use  Assumes that all watersheds are exactly alike

except for the size of the watershed

 Rainfall-Runoff Models (HSPF, Sacramento Soil

Moisture Accounting Model)

 Physically based but parameter-intensive  Used by NOAA for flood forecasting  Requires long stream gage period-of-record for

site calibration and validation

 The QPPQ Transform method has been adopted

• r is being considered by several US Geological

Survey district offices:

 Massachusetts and Rhode Island USGS  Pennsylvania USGS  Iowa USGS  Minnesota USGS  New York USGS  New Hampshire and Vermont USGS

Does USGS Like QPPQ Transform?

 The QPPQ Transform method was extensively

tested by the USGS and bested 17 alternative methods for estimating daily flow time series at 182 gaged watershed sites located in

 West Virginia  Tennessee  North Carolina  South Carolina  Georgia  Alabama  Florida

Has the QPPQ Been Extensively Tested?

 The QPPQ Transform method has been adopted

• r is being considered by several state agencies:

 Massachusetts EOEEA  Massachusetts Water Management Act

program

 Sustainable Water Management Initiative  The Delaware River Basin Authority  Maryland Dept. of the Environment  New Hampshire  Vermont

Have States or Agencies Adopted the QPPQ?

 The QPPQ Transform method has been used for  Many surface water reservoir system

assessments in Massachusetts and Connecticut

 River basin and watershed studies in

Massachusetts and Connecticut

 Systems analysis study of the Connecticut

River watershed

 Complex litigation in Connecticut

Examples of Local Applications

The QPPQ Transform Method

Four Steps to the QPPQ Transform Method

• 1. Chose a USGS Streamgage Site for the time

series: Qgage(t)

• 2. Use that time series to construct a streamflow

duration curve (FDC): Qgage(p)

• 3. Construct a FDC at the ungaged site using its

watershed’s soil characteristics, climate, and topography and a regional FDC model: Qungaged(p)

• 4. Generate a streamflow time series at the

ungaged site: Qungaged(t)

Minnesota

USGS 2016

Use Qgage(t) to Construct ‘observed’ FDC Qgage (p)

 Rank sort Qgage(t) “n” days from largest to smallest

Q(1) ≥ Q(2) ≥ Q(3) … Q(n-2) ≥ Q(n-1) ≥ Q(n)

POR 30 years x 365 = 10,950 days P[Q≥Q(n)]x100 =10,950/10951 x 100 = 99.991

 “i” is the rank-order i=1,n  “n” is number of days in the period of record  Use “plotting position” formula to estimate

exceedance probability p=P[Q≥q]

Step 1: Qgage(t) and Step 2: Qgage(p)

 Common factor between the flow date, time, and

the FDC probability, p, is Q = a 3-D relationship

 Knowing Q gage (t) & p(Qgage) => p(t)

Update Step 3: Regional FDC Model

 HYSR study focused on update of the Fennessey

(1994) regional FDC model: Qungaged(p)

 Constructed a streamgage network of USGS

gaged watersheds found in both the HCDN (1992) and GAGES-II (2010) national streamgage networks

 All gages have at least 20 years POR in 1950-

1990 base-period

 HYSR prelim. network of 142 gaged watersheds in

ME, NH, VT, MA, RI, CT, NH, PA, and NJ

Step 3: Regional FDC Model

 Need a FDC for the ungaged site without historic

daily streamflow data

Assess Alternative Probability Function Candidates for Regional FDC Model

 Statistically analyze each of the 142 gage site

POR to estimate the L-moments (linear probability weighted moments)

 Construct a L-kurtosis Diagram to compare

alternative probability functions

 Conduct Discordancy analysis to determine the

“region”; eliminate sites “outside” the core region

 8 NJ gage sites and 1 PA site near NJ eliminated  Final HYSR network: 133 USGS stream gage

sites, 20-year POR in 1950-1990 base period

Final Probability Function Candidates

 Three-parameter Generalized Pareto (GPA)  Three-parameter Log Normal (LN3)  Fennessey (1994) conducted extensive “goodness

• f fit” tests on both and chose the GPA.

 Use L-moments to calculate the 3 parameters:

ζ, α, κ for each of the 133 HYSR network sites

 Test the “fitted” FDC against the “observed” FDC

Baker River, near Rumney, NH

Construct Regional FDC Model

 Gather HCDN and GAGES-II network watershed

specific soil, climate, and topography data for each

• f the 133 USGS gage sites in the HYSR network

 Use each of the 3 GPA parameters statistically

determined for each of 133 HYSR watersheds from the streamgage data as dependent variables

 Use OLS multivariate regression and each

watershed’s specific soil, climate, and topography data as candidate independent variables

 Keep only those particular soil, climate, and

topographic variables that are “statistically significant” (pass various tests)

 To construct a FDC at the ungaged site, the analyst

must determine ten soil, climate, and topography characteristics for that watershed:

 Watershed area (mi2)  Avg annual precipitation (in/yr)  Avg annual temperature (oF)  Potential maximum soil moisture retention (in)  Percent of watershed area covered by HSG C soil (%)  Avg watershed elevation (ft)  Avg watershed aspect (degrees) 0-360O  Percent of watershed area covered by lakes, ponds and

reservoirs (%)

 Percent of watershed area covered by impervious surface (%)  Slope of main stream channel (ft/mile)

Baker River, near Rumney, NH

Compare FDCs and Assess “Goodness-of-Fit”

 Construct “observed,” “fitted,” and regional “model”

FDCs at eleven NH USGS gages sites, watershed areas range: 12.1 mi2 – 622 mi2

 Graph all three FDCs for visual comparison  Estimate the Bias and RMSE between the

“observed” FDC and the “fitted” FDC to see how suitable the GPA is as basis for the Reginal FDC Model

 Estimate the Bias and RMSE between the

“observed” FDC and the regional “model” FDC to see how well it compared with the “fitted” FDC.

 GPA is a good choice for regional FDC model  “Fitted” FDC is good compared to “obs.” FDC  Parsimonious: only 3 parameters to estimate  Regional FDC model regression equations  Ten watershed variables are estimated from GIS

data layers and USGS topographic maps

 “Model” compares well to “fitted” FDC  Regional FDC model is continuous and monotonic  Because E[P] and E[T] are independent variables,

can do assessment of potential impacts on streamflow due to climate change

Regional FDC Model Development Conclusions

QPPQ Transform Steps 1 - 3

Step 4: Generate Qungaged(t)

 Assume for Steps 2 and 3: p(Qungaged) = p(Qgaged)  Recall 3-D relationship between t, Q and p => p(t)  Use regional FDC model with p(t) instead of just p

Summary

 The QPPQ Transform method was conceived and

developed by Fennessey (1994)

 The method has been widely adopted  The Step 3 regional FDC model was updated in the

present HYSR study

 The goals of the QPPQ Transform remain the same:  Provide method to generate a quality time series

• f daily streamflow data at ungaged sites

 The analyst can choose to do whatever they want

with the generated time series, Qungaged(t)

Questions and Comments?

Neil M. Fennessey Hydrologic Services 49 School Street South Dartmouth, MA 02748 HYSRConsult@gmail.com