Cumulative Precipitation

Transcription

1 Problem 1: Hyetograph Construction (4 pts) Use the rainfall information below to construct both the cumulative (inch) and incremental (in/hr) hyetographs. Note: the incremental hyetograph must be formatted in the manner discussed in class (no gaps between bars, unless there is a period of no rainfall), to get any credit. Precip (in) SOLUTION The information is given as cumulative hyetograph, thus no data manipulation is needed, just perform a line plot Cumulative Precipitation Precipitation (in) (hours) For the incremental, the data must be converted depth per time period (in/0.25hr), so each current value needs to have the previous value subtracted from it. Next convert to in/hr. Plot as a bar plot. To remove spaces between bars, right click on click on format data series and move the gap width bar to no gap. Spring 2013 Page 1

2 Intensity (in/0.25 hr) Intensity (in/hr) Precip Frequency (in/hr) Hyetograph (hours) Problem 2: Hydrograph & Hyetograph Analysis (6 pts) Use the precipitation event from the previous problem and assume 10% of the water infiltrates. Using the flow data provided below, calculate the volume of water that evaporates across the 60 acre watershed. Assume depression storage is negligible. What do we know about base flow? Why? SOLUTION To solve, the total volume of discharge must be calculated, and converted to a depth. Dischage*time (cfs*hr) Spring 2013 Page 2

3 sum Since 10% of the precipitation infiltrates, 90% stays above ground: Thus the evaporation volume is Problem 3: Porosity and Soil Relationships (8 pts) A cubic meter of soil has the following characteristics: 0.65 m 3 is solid soil 0.18 m 3 is water The rest is air Answer the following questions: 1. (1 pt) What is the porosity of the soil? 2. (1 pt) According to what kinds of soil could this sample be? 3. (1 pt) What is the specific yield? 4. (1 pt) What is the specific retention? 5. (2 pt) If there was an acre of this same exact soil, what is the maximum volume of water (ft 3 ) that would be stored in the three feet of soil? 6. (2 pt) The soil was analyzed and it contains 60% silt and 20% sand, what is the soil classification? (turn in your ternary diagram to get credit) SOLUTION Spring 2013 Page 3

4 2. Soil possibilities: gravel, sand, silt, (note that Fractured Basalt and Karast Limestone are not acceptable answers as these are rocks and not soil) Silty Loam ,738 Problem 4: Baseflow Separation (12 pts) Using the hydrograph information below (you can download the supplemental spreadsheet from the website), separate the baseflow from the hydrograph using the a. Constant Method b. Constant Slope Method c. Concave Method For each method show your excel calculation tables and a plot that shows the pre-baseflow removal hydrograph, the baseflow and the post-baseflow separation (like we did on the in-class Spring 2013 Page 4

5 example). Assume the falling limb inflection point occurs at hour 8.5. Answer the following questions: 1. Which method would lead to the most conservative hydrologic flood planning design? 2. Which method would lead to the least conservative hydrologic flood planning design? 3. What would you need to do to know the differences of runoff for each method? SOLUTION (see spreadsheet too) Constant Baseflow DRO Spring 2013 Page 5

6 Hydrograph Baseflow DRO (hours) Constant Slope Baseflow DRO Spring 2013 Page 6

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8 100 Hydrograph Baseflow DRO (hours) Concave Baseflow DRO Spring 2013 Page 8

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10 100 Hydrograph Baseflow DRO (hours) Questions 1. Most conservative flood design = least baseflow = Constant 2. Least Conservative flood design = most baseflow = Constant Slope 3. How know for sure? Integrate under each curve (find area below curves) Problem 5: Watershed Delimitation (10 pts) For this problem your point of analysis (outlet) will be just southwest of the University of Utah Orthopedic Center, at the corners of Foothill drive and Wakara Way. The coordinates are approximately Long: , Lat: Using only Google Earth and the supplemental topographic map (courtesy of Delineate the watersheds that would contribute to flow past this location. Make sure to hand in a copy of the hand drawn watersheds on a map. SOLUTION Not posted due to this being a part of your semester project. Problem 6: Rational Method (8 pts) Using the watershed you delineated above, Do a simple analysis of both the current watershed and the likely predevelopment watershed (before buildings) to calculate both the predevelopment and postdevelopment peak outflows using the Rational Method. Use a 25 year storm and assume the time of concentration is 45 minutes and the area is 250 acre. Do a weighted average to get your runoff coefficient if needed. Be sure to state any assumptions you make. Spring 2013 Page 10

11 SOLUTION Rational Method: Area = 250 ac For rainfall intensity, need precip freq curves. The 25 year, 45 minute storm intensity is needed. Be sure to set the output to intensity not depth. Spring 2013 Page 11

12 2 Now we need C: Current (post-development) Runoff Coeff Spring 2013 Page 12

13 From the image, it looks like there are the following types of cover: forested, meadow, commercial (research park is similar setup to commercial), streets, parking, open space. Rough estimates of land cover percentage: Assume soil type C. Assume on the mountain, slope is > 6% and in the valley it is 0-2%. The weighted average would be: Predevelopment Runoff Coefficient Cover Type % Forest 30 Meadow 30 Commercial 20 Street 5 Parking 10 Open Space 15 Assume the mountain has not changed. Assume the valley was pasture: Now can calculate Q peak., , Spring 2013 Page 13