Determine streamflow duration curve and base flow index (BFI) for USGS gaging station 01540200, Trexler Run near Ringtown, PA.

A) Go to the USGS website for streamflow data: http://waterdata.usgs.gov/nwis/sw.

Select "Daily data"

for "Choose Site Selection Criteria" select "Site Number" and hit submit

for "Select sites" enter Site Number 01540200

for "Available parameters..." select Streamflow ft³/s or Streamflow m³/s

for "Choose Output Format" select date range of 1963-09-01 to 1981-03-31

select "Tab-separated data" and "Save to file".

click submit

Using a spreadsheet, calculate mean daily flow for the period of record. Calculate the flow duraction curve according to Equation (4.5). Determine Q_0.1, Q_0.25, and Q_0.5.

If base flow is equivalent to Q_0.5, what is the BFI?

B) Go to the USGS website for streamflow statistics: http://streamstats.usgs.gov

read through Streamstats description, limitations, definitions, and user instructions.

Click on "State Applications", and then select Pennsylvania.

Zoom to "Place Name".

On new window, enter Trexler Run and select "stream" and " Pennsylvania" and click submit query.

Click Zoom in the new window and the stream and gage location are displayed in the viewer window.

On the left side of the viewer window, check "Stream Gages" under Map Contents. A cyan colored triangle will mark the location of stream gage number 01540200.

From menu bar select "Gaging Station Information", then place cursor over gage symbol on map and left click. A window with stream statistics will be displayed.

Compare estimates of Q_0.1, Q_0.25, and Q_0.5 in this window with those calucated in problem 4.1A.

Convert Q_0.1, Q_0.25, and Q_0.5 from volumetric flow to inches or mm per unit drainage area of stream. Next, convert these numbers to percentage of annual average precipitation.

What other sources of data might be helpful for analyzing streamflow at this site?

Problem 4.2

Using the StreamStats web site, select an ungaged location on a stream, delineate the contributing area to that point, and use tools available on the web site to estimate flow statistics.

Problem 4.3

Apply and analyze streamflow hydrograph separtion methods for USGS gaging station 01540200, Trexler Run near Ringtown, PA by using the Web-based Hydrograph Analysis Tool (WHAT).

Select 1) WHAT Using USGS Daily Flow Data i) I will enter USGS gaging station number

Enter station number 01540200 and select i

Select "local minimum" option

From the results, determine the base flow index (BFI) for the entire period of record, for each year based on average annual flow, for the month of May over the entire period of record, and for the month of May for each year.

Draw a hydrograph of daily total flow and base flow for one year

Rerun hydrograph analysis using One Parameter Digital Filter and Recursive Digital Filter. Calculate BFI for entire period of record.

Compare and discuss the different estimates of BFI.

Problem 4.4

Apply and analyze streamflow recession curve displacement method for USGS gaging station 01540200, Trexler Run near Ringtown, PA.

Download the USGS programs Recess (for calculating the Recession Index, K) and Rora (for estimating recharge) from: http://water.usgs.gov/software/lists/groundwater.

Following directions in problem 4.1, download streamflow data in cfs for station number 01540200 Trexler Run near Ringtown, PA.

Run program Recess to determine the Recession Index; set number of days in recession to 21.

Run Rora to determine base flow on a monthly and annual basis by using the value of Recession Index determined with Recess. Note, the drainage area for the gaging station must be added to file station.txt for Rora to run.

Perform some sensitivity tests:

How sensitive is the value of calculated Recession Index to the number of days that are specified for the recession period?

How sensitive are estimates of base flow to values of Recession Index?

How do estimates of baseflow and BFI compare between the Recession curve displacement method and hydrograph separation methods?

Referring back to the flow duration curve calculated in Problem 4.1, what recurrence levels do the different BFIs determined in these examples reflect?

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