Faculty of Applied Science and Engineering. Department of Civil Engineering. Hydrology and Hydraulics. Final Exam, April 21, 2017

Transcription

1 F Name: Student #: University of Toronto Faculty of Applied Science and Engineering Department of Civil Engineering C1V250 - Hydrology and Hydraulics Final Exam, April 21, 2017 Duration: 2 and V2 hrs The test is 11 pages and graded out of 70 marks. Test is closed book, only a non-progranirnable calculator, rulers and a two-sided 8 ½" x 11" aid sheet is permitted. All work must be neat and legible. Show all your calculations and state any assumptions. Answers are to be written in exam booklets. Your equation sheet must be submitted with your exam at the end of the examination period. Page! of 11

2 14 TERMS AND CONCEPTS marks] Define and describe 3 of the following (use sketches when appropriate): Effective Rainfall Field Capacity Stage Lysimeter CONCEPTUAL QUESTIONS 14 mark] What are the two resistance factors caused by plants that affect evapotranspiration? Describe these two types of resistance factors and how they affect evapotranspiration rates. Use sketches where appropriate. 14 marksl What function do the weirs provide in the Humber River? Many of the weirs along the Humber River have trapezoidal notches removed from the center of the weir. Why was this done? Was this intervention successful? Why or why not? Page 2 of 11

3 COMPUTATION QUESTIONS. 4. The stormwater management system of a proposed 1.8 ha commercial development needs to be designed for a storm with a 25 year return period. The 25-year IDF curve is given by: t + 33 Where i is the rainfall intensity in cm/hr and t is the storm duration in minutes. Local regulations require a minimum time of concentration of 10 minutes. The development has a Manning's n for overland flow of 0.016, an average overland flow length of 90 m and an average slope of 0.6%. 110 marks] Determine the flow rate that will govern the design of the storm sewer. The time of concentration can be modelled using the kinematic wave equation. 18 marks] The developer is considering directing the runoff to a reservoir for storage. In order to size the reservoir you need to determine the total volume of runoff that needs to be stored. Use the NRCS curve number method to estimate the total volume of runoff for a 2 hr design storm, assuming the soil has an average condition at the beginning of the design storm. An infiltration test on the soil shows that the minimum infiltration rate is 2 mm/hr. Page 3 of!!

4 5. Discharge data was recorded during a 2-hr rain event at the outlet of a 200 km2 watershed. The data is plotted in Figure 1. The stream outflows into a 50 ha lake. Hydrograph D Time (hrs) Figure 1-2-hr Streamfiow Hydrograph (i) [15 marks] Create the hydrograph for a 7 hour, 4.5 mm rainfall event. You may draw on Figure 1 on this page to show your work. Include a sketch that graphically represents your process using the graph paper provided in Figure 2 and label each series. Clearly show all intermediary steps and calculations for creating this hydro,iraph. Page 4 of!!

5 Figure 2- Graph Paper for Question 5 (i) [4 marks] The municipality is considering diverting a portion of the river for a microhydroelectric project. They require a 10 m3/s discharge through the diversion channel for the project to be successful. They have designed a 3 m wide rectangular concrete lined diversion channel with a slope of 0.1 % to be used to divert the water for this project. What depth of channel is required to accommodate this discharge? [2 marks] Will the flow in the channel designed above be sub-critical or supercritical flow? Page of!!

6 6. A site consists entirely of a sandy loam soil and has 4 mm of depression storage. Assume the initial moisture content is Using the Green and An-pt Method, [2 marks] Determine if and when ponding begins during the storm. 115 marks] Determine the incremental and cumulative runoff from the site using the following design storm. Interval (mm) Average Rainfall (mm/hr) End of Exam Page 6 of 11

7 Flow Wetted Hydraulic Shape Section Area A Perimeter P Radius R 77 (b + zy)y Trapezoidal y y(h+zy) b +2y1+z2 b+v1+z2 Triangular NI Z Y 7 zy 2 2y v1 + ZY Rectangular E _ by by b + b 2v - A V Wide flat I by b y -b >>y-- Circular b S (0 sino ç - sin 0 Copynght 32O13 Pearson Education, publishing as Prentice Hall Page 7ofll

8 Table 16.5 Rational Runoff Coefficient Urban Catchments General Description C Surface C City Asphalt paving Suburban business Roofs Industrial 0.5-0,9 Lawn heavy soil >7 slope Residential multiunits Housing estates < Bungalows Lawn sandy soil > Parks, cemeteries < Rural Catchments (less than 10 km2) Ground Cover Basic Factor Corrections: Add or Subtract Bare surface 0.40 Slope < 5%:-0.05 Grassland 0.35 Slope> 10%: Cultivated land 0.30 Recurrence interval <20 yr: Timber 0.18 Recurrence interval > SO yr: Mean annual precipitation <600 mm: Mean annual precipitation> 900 mm: Source: Stephenson (1981). Page 8 of 11

9 Table 4.6 Green-Ampt Infiltration Parameters Wetting front soil Effective hydraulic Soil texture class Porosity, 9 suction head, S1, cm conductivity, K, cm/h Sand 0,437 4, ( ) ( ) Loamy sand 0, ( ) ( ) Sandy loam ( ) ( ) Loam ( ) ( ) Silt loam 0,501 16,68 0,34 ( ) ( ) Sandy clay loam 0, ( ) ( ) Clay loam ( ) ( ) Silty clay loam ( ) ( ) Sandy clay 0, ( ) ( ) Silty clay 0, ( ) ( ) Clay , ( ,523) ( ) Source: Rawls and 8rakensiek (1983). Table 4.10 Hydrologic Soil Groups Minimum Infiltration Rate Group Range (rnm.hr) Texture' A Sand, loamy sand, or sandy loam Silt loam or loam C Sandy clay loam D Clay loam, silty clay Foam, sandy clay, silty clay, or clay a Reproduced from U.S..Soil Conservation Service (1986. Page 9 of It

10 Table 2-1 Runoff Curve Numbers for Selected Agricultural, Suburban, and Urban Land Use (Antecedent Moisture Condition II; 0.25) Hydrologic Soil Group Land Use Description A B C D Cultivated land' Without conservation treatment With conservation treatment Pasture or range land Poor condition Good condition Meadow Good condition Wood or forest land Thin stand, poor cover, no mulch Good cover Open spaces, lawns, parks, golf courses, cemeteries, etc. Good condition: grass cover on 75% or more of the area Fair condition: grass cover on 50%-75% of the areai Commercial and business areas (85% impervious) Industrial districts (72% impervious) Residential3 Average lot size Average % impervious4 1/8 ac or less ac /3 ac /2 ac lac Paved parking lots, roofs, driveways, etc Streets and roads Paved with curbs and storm sewers Gravel Dirt Factor to convert runoff volume to depth Unit of Runoff Unit of Unit of Unit of Unit of K Ordinate Time Base Volume Area depth m3/s day m3/s*day km2 mm 86.4 m3/s hour m2/s*-hr km2 mm 3.6 Conversions: 1 ha = 10,000 m2 1 nun = in Page 10 of 11

11 Table 14.4 Values of Manning's Roughness Coefficient' Material Closed conduit or built-up channel 1.1 Metal Manning n Brass 0.01 Copper Steel welded Steel riveted Cast iron coated Wrought iron galvanized Corrugated metal (storm drain) Nonmetal Glass 0.01 Cement Cement mortar Concrete culvert Concrete lined channel/pipe Wood Clay Brickwork 0,013 Brickwork with cement mortar Masonry/ rubble masonry Sanitary sewer coated with slime Asphalt Plastic PVC ,011 Polyethylene Excavated or Dredged Channel Straight and clean Winding and sluggish Dredged Rock cut/stony Earth bottom, rubble sides 0.03 Unmaintained/uncut brush 0.08 Natural streams On plain, clean, straight, no pools 0.03 On plain, clean, winding, some pools 0.04 On plain, sluggish, weedy, deep pools 0.07 On mountain, few boulders 0,04 On mountain, large boulders 0.05 a For overland flow roughness coefficient see Table Note: Judgment must be used to determine n for channel characteristics that fall in between these categories. See Chow (1959) for a detailed reference. Page!! of 11