Objective


You have been asked to study the climate at Oroville. Using NCDC and CDEC data gathered in the previous workshop, you will be asked to compare and determine the relationship (if any) between temperature, precipitation, and inflow for Oroville.

Task 1. Acquire and Prepare Data

Data has been gathered from the National Climatic Data Center (NCDC) for you, and the files with an extension of ".ncdc" can be downloaded at the link below.

8184491927172.ncdc

8184491927172 (1).ncdc

8184491927172 (2).ncdc

  1. Launch HEC-DSSVue; create a new DSS Version 7 file named "nOro.dss"
  2. Drag and drop the .ncdc files onto DSSVue to import them.
  3. If the import seems hung, hit F5
  4. Plot the daily precipitation for Bush Creek, a gage in the Oroville watershed.


Question 1. Can you gather anything about the seasonality of  the precipitation from this plot?

Nope. 


Let's make some sense from this precipitation data and changing the daily incremental precipitation into monthly precipitation and running a cyclic analysis :

     5. Clear all selections; Select Bush Creek daily precipitation

     6. (//BRUSH CREEK RS/PRECIP-INC//1DAY// )

     7. Open the Math Functions

     8. In Time Functions, select the operator Min/Max/Avg… Over Period

     9. Select the Function Type Accumulation over Period

     10. Set period = 1MON.

     11. Press compute.

     12. Now change to the Statistics tab and select cyclic analysis.

     13. Compute and plot the average, max and min.

Question 2. What can you gather from this data now?

December and January are the big rain months – not so much in spring.  Summer and fall are dry.  It doesn’t rain in August.

     14. Repeat the procedure for maximum temperature (TMAX), EXCEPT select "Average over Period" when you compute monthly data.

     15. Plot the cyclic analysis results.


Question 3.  What is the maximum average temperature for August? What is the minimum average temperature for December?

As the rain increases, the temperature decreases and vice versa. The maximum average temperature in August is 101 degrees and the minimum average temperature in December is 47 degrees. It rains most in December, when the temperatures are lower.


Keep handy both the precipitation and temperature plots. (If you want you can save to .png, or copy into a Word doc.)


     16. Look at the Oroville inflow that you retrieved earlier in the Oroville.dss file

    1. Plot //ORO/RESERVOIR INFLOW/01JAN2021/1DAY/CDEC/

Question 4.  What do you think about the quality of the data?

Looks like there may be some questionable values


     17. Let's clean up the data:

    1. Select the data set and go into the math functions module.
    2. In the General Tab "Screen using Minimum and Maximum".
    3. Set the Minimum Value = "0"
    4. Leave invalid values as missing.
    5. Leave the rest of the fields blank.
    6. Compute. Plot.


     18. Because there might be missing values, the CDEC importer could have stored the data as irregular-interval data. However, the statistics functions require regular interval data
If the inflow data is IR, Convert the data set to regular interval:

    1. In the Time Functions Tab select Irregular to Regular
    2. Select a time interval = 1Day
    3. Save your modified data.
    4. Close the math functions module.

Task 2. Analyze Data

  1. Perform a Cyclic Analysis of Flow:
    1. Select the regular interval, daily inflow data set that you just produced.
    2. Open the Math Functions to the Statistics tab
    3. Compute a Cyclic Analysis
    4. Plot the 25th, 50th and 75th percentiles together.
  2. Now view this plot next to the precipitation and temperature plots that you computed earlier.

Question 5. What do these plots tell you about the seasonality hydrometerologic conditions? 

Most of the inflow is in late winter and spring.  This is after most of the precipitation has already fallen.  April and May have significant inflows.  December inflows are not that great, even though most of the precipitation occurs at this time.  Looking back at the temperature plots, there is not much flow when it is cold and there is a lot of precipitation; however there is a lot of inflow when it warms up.  Sounds like most of the inflow is coming from snowmelt.

      3. Perform two duration analysis on the daily inflow data:

    1. Clear all selections and select the regular interval daily flow data
    2. Open the Math Functions to the statistics tab
    3. Use a duration analysis
    4. Use the standard method
    5. Make the Horizontal axis probability
    6. Make the vertical axis log
    7. Compute and Plot and move the plot to the side
    8. Select Restore Original Data under Edit.
    9. Change the Vertical axis to Linear.
    10. Compute and plot.

Question 6.  Which plot is more useful when looking at low flows?

 The log plot shows greater clarity at low flows – this is often what a duration analysis is used for. 

Question 7. The fish in this reach are at risk when flows are less than 100 cfs, what percent of the time does that occur?

 Using the log plot, flows exceed 100 cfs about 99.7% of the time. Fish are in trouble approximately  0.3% of the time. 


You can download the solution files here: Math Functions - Statistics Solution.7z