Question

QUESTION 18

What kind of curve is used in stream gauging to relate water surface to discharge?

		flood frequency curve
		rating curve
		depth-duration-frequency curve
		intensity-duration-frequency curve

QUESTION 19

What kind of curve results from the statistical analysis of annual peak discharge date from a stream gauge?

		flood frequency curve
		rating curve
		depth-duration-frequency curve
		intensity-duration-frequency curve

QUESTION 20

What might the HEC-SSP computer program be used for?

		Evaluating USGS Regional Regression Equations easily.
		Performing statistical analysis of stream gauge data.
		Estimating discharge by the Rational Method.
		None of the above.

Answer 1

Answer 19 - Rating curve

Because a rating curve is a graph of discharge versus stage for a given point on a stream, usually at gauging stations, where the stream discharge is measured across the stream channel with a flow meter. The rating curve is usually plotted as discharge on x-axis versus stage (surface elevation) on y-axis

Answer 20 - flood frequency curve

Because A flood frequency curve is a tool to extrapolate how often a flood of a given discharge will occur. A flood frequency curve can be constructed by plotting a graph of discharge versus recurrence interval. This can easily be accomplished provided you have a data set of annual peak discharge measured over a number of years.

Your flood discharge data should list the year and the given discharge in velocity that occurred that year. You need to calculate the order of each of the floods. Start by ordering your data according to the magnitude of the flood, from smallest to largest. Number each of the floods in order, starting with the smallest flood as number "1". The order of the flood is denoted by the letter "m". If you have 100 years of records, you will calculate flood orders for m=1, m=2, m=3,....m=100.

Calculate the recurrence interval, which is the number of times in your record that a flood of a given magnitude occurred. The formula for recurrence interval is. T= (n+1)/m Where T= recurrence interval, n=number of years in the record, m= the number you calculated in step 2, the order of the annual flood discharge. You should, therefore, calculate the recurrence interval for each year of data you have. For instance, if you have 100 years of flood records, you will have floods numbered from 1 to 100, and you will calculate 100 recurrence intervals. Write the recurrence interval beside each given flood.

Construct your graph on the semi logarithmic paper. Recurrence interval will go on the x axis; and discharge will go on the y axis. Divide the x axis with the following scale: 1, 1.5, 2, 4, 6, 8, 10, 20, 50, 100, 200. Label the axes, and title your graph “Flood Frequency Curve”.

Plot corresponding discharges and recurrence intervals.

Draw a best fit line between the data set. The resulting line is the flood frequency curve.

Answer 21 - Performing statistical analysis of strain gauge data

Because U.S. Army Corps of Engineers Statistical Software Package (HEC-SSP) developed by the Hydrologic Engineering Center. This software allows you to perform statistical analyses of hydrologic data. The current version of HEC-SSP can perform flood flow frequency analysis based on Bulletin 17B, "Guidelines for Determining Flood Flow Frequency" (1982), a generalized frequency analysis on not only flow data but other hydrologic data as well, a volume frequency analysis on high and low flows, a duration analysis, a coincident frequency analysis, and a curve combination analysis.

Statistical Analysis Components

• Flow Frequency Analysis

• General frequency analysis

• Volume frequency analysis

• Duration analysis

• Coincident frequency analysis

• Curve combination analysis