University of Colorado
Department of Civil, Environmental and Architectural Engineering
Engineering Hydrology
CVEN-4333 Spring 2006
Finals (Take Home)
Date: 05/06/2006
Due: 05/06/2005 – 5PM (if you picked up in the morning)
or
Due: 05/07/2005 – 9AM (if you picked up in the evening)
Total 70 points
______________________________________________________________________________________________
Please write the steps clearly so that points can be awarded even when the
numerical answers are incorrect. You can use textbook/class notes,
calculators/Excel. Refrain from consulting with each other – I trust your
conscience and honor system.
Infiltration
1. Consider the following storm:
Time (h)
0-2
2-4
Rainfall Intensity (cm/h)
0.5
2
Philip's equation is applicable with Kp = 0.2 cm/h and Sp = 3 cm/h^0.5.
(a) When does ponding first occur in this storm?
(b) Determine the Total infiltration and the excess rainfall at the end of 4hrs.
[3,6,1]
[Hint: You can look at it as two separate storms joined together – so you can analyze each one
separately]
2.(a) Show that the ponding time under rainfall of intensity i for a soil described by Horton’s
equation with parameters fo, fc and k is given by
Tp = (1/i*k) [fo – i + fc* [ln( (fo – fc) / (i – fc) ) ]
Where Tp is the time to ponding
[Hints: follow the steps outlined in the class that we used to get a similar expression for Philip's
equation - From the infiltration rate equation re-arranged to get an expression for time ‘t’; plug
this into the cumulative infiltration equation; and set this equal to cumulative infiltration at
ponding and re-arrange]
(b) Calculate the cumulative infiltration (F) and the infiltration rate ( f ) after one hour of rainfall
at 5 cm/hr on a soil with Phsi = 64.4cm, hydraulic conductivity, K = 2.59 cm / hr and deltaTheta
= 0.035. What is the time when the cumulative infiltration will be twice as much as it is at the end
of the first hour.
[5, 5,2,3]
Unit Hydrograph / Runoff
3. Measured total hourly discharge rates (cfs) from a 2.48 square miles drainage basin are
tabulated below. The hydrograph was produced by a rainstorm having a uniform intensity of 2.6
in/hr starting at 9 A.M and ending at 11 A.M. The baseflow for the entire period was a constant
100 cfs
Time
8AM 9
10
11
12
1PM 2
3
Total discharge (cfs)
100
100
300
450
300
150
100
100
(a) At what time did direct runoff begin?
(b) Determine the excess rainfall depth (the total rainfall is of course, 2.6 x 2 = 5.2 inches).
( c ) Derive a 2-hr Unit hydrograph
[1, 5, 4]
4. You are in-charge of delineating the flood plain for the South Boulder Creek. To do this you
have to estimate the peak discharge corresponding to a 100-year 1-hour design storm, which will
be passed through a flood plain model for delineation. The peak discharge is obtained from the
outflow hydrograph – which in turn is obtained by convoluting the excess rainfall with the unit
hydrograph. The following information is provided:
(i) The 100-year design rainfall for 1-hour duration is 3.0 inches
(ii) The area of the watershed is 132 square miles
(iii) The time of concentration (Tc) for this watershed is 1.5 hours
(iv) Assume antecedent moisture condition to be wet (i.e. AMC III). The SCS curve number for
normal antecedent moisture condition (AMC II) is 84.
You have to obtain (a) Excess Rainfall (b) the Unit Hydrograh and ( c ) the peak discharge by
convolution
[5, 4, 6]
Course Synthesis
6. You are now the team leader to design a reservoir in the Pacific Northwest. Assume that you
have access to monthly flow data at a nearby gauge on the river and no other data. Having been
exposed to a wide ranging aspects of the hydrologic cycle and large-scale climate in the
Hydrology course – outline the steps in your design process.
[5]