Baseflow Separation PhiIndex Determining the index and Excess Rainfall Hyetograph Direct Runoff from the SCS Curve Number Equation Midterm Format Open Book Answer all questions Please answer on separate sheets of paper You may refer to the textbook notes solutions to ID: 582319
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Slide1
Midterm Wrap up and ReviewSlide2
Baseflow SeparationSlide3
Phi-IndexSlide4
Determining the index and Excess Rainfall HyetographSlide5
Direct Runoff from the SCS Curve Number EquationSlide6
Midterm Format
Open Book.
Answer all questions. Please answer on separate sheets of paper. You may refer to the textbook, notes, solutions to
homeworks and any other written or printed reference material that you have brought with you. Calculator use. You may use a programmable calculator or equivalent calculating device (e.g. calculator functionality on a phone). You should limit the use of the calculating device to the performance of calculations. You may use programs that you have written to evaluate quantities commonly used in this class (e.g. saturation vapor pressure). You may not send messages or access the internet or communicate in any way with anyone other than the instructor or moderator regarding solutions to these questions.Slide7
Learning Objectives
Hydrologic data, the hydrologic cycle and water balance (HW 1)
Work with hydrologic data, quantify uncertainty and variability, and apply conservation laws to the solution of hydrologic problems.
The Climate System and Global Hydrology (HW 2)Analyze the global energy balance and sensitivity of surface temperature to factors involved, such as albedo and the greenhouse effect. To quantify the water balance and its sensitivity to climate for a watershed of interest.Slide8
Learning Objectives 2
Precipitation (HW 3)
Estimate area average precipitation from point measurements using a variety of methods
Quantify the uncertainty in an areal precipitation estimateEstimate design rainfall amounts and intensities[Use ArcGIS for analysis of hydrologic data]Slide9
Learning Objectives 3
Runoff generation and water in soil (HW 4)
Use the terminology used in hydrology and the study of rainfall-runoff processes (Workbook chapter 1).
Describe the processes involved in runoff generation (Workbook chapter 2)Distinguish between infiltration excess, saturation excess and subsurface stormflow runoff generation mechanisms and identify when and where each is more likely to occur (Workbook chapter 2)Describe the physical factors resulting in the occurrence of runoff by the different mechanisms (Workbook chapter 3)Quantify the properties of water held in and flowing through soil (Workbook chapter 4)Slide10
Learning Objectives 5
Infiltration (HW 5)
Calculate infiltration, infiltration capacity and runoff rates using the methods described in the Rainfall Runoff Processes workbook chapter 5
.Slide11
The Hydrologic Cycle
From Ross WoodsSlide12
Atmospheric Water
Soil Water
Surface Water
Groundwater
Water Balance
Change of Storage
= Inflow - OutflowSlide13
Watershed water balance
P
ET
Q
G
out
G
in
SSlide14
Storage-Yield Analysis
Used to size a reservoir given a streamflow time series
.
Sequent Peak Procedure
K
t
= K
t-1
+
R
t
–
Q
t
If
K
t
< 0,
K
t
=0
S = Max(
K
t
)
R
t
= ySlide15Slide16
The climate system and global hydrology
Perform simple analysis
of the global energy balance and sensitivity of surface temperature to factors involved, such as albedo and the greenhouse
effectSlide17
The Greenhouse Effect - Two
layer atmosphere energy balance
W
Refer to Box 3-2 for definitions of quantities and numerical estimates of parametersSlide18Slide19
General Circulation of the Atmosphere
Slide from Simon WangSlide20
Water Balance (Budyko
curve
)
Evapotranspiration fraction
Dryness (available energy /
precip
)
1
humid
arid
energy limited
water limited
R/P
E/P
E = R : energy limited upper bound
large
small
Soil Storage/ Retention
or Residence time
medium
E = P : water limited upper bound
Increasing variability in soil capacity or areas of imperviousness
Increasing variability in P – both seasonally and with storm events
Increasing
Retention or Soil
capacitySlide21
Precipitation
Area AveragingSlide22
Climatology and statistical Variability
http
://dipper.nws.noaa.gov/hdsc/pfds
/
Slide23
From Bras, 1990
Uncertainty in Areal precipitationSlide24
Physical Processes involved in Runoff Generation
Rainfall Runoff ProcessesSlide25
(a) Photograph of cross section through soil following dye tracing experiment. (b) Moisture content inferred from dye tracing experiment. (Courtesy of Markus Weiler)
Infiltration follows preferential pathwaysSlide26
See infiltration excess runoff generation animation
http://hydrology.neng.usu.edu/RRP/
(
ch 2)
Runoff Generation Mechanisms
(a) Infiltration excess overland flow
(also called Horton overland flow)
P
P
P
q
o
f
f
(following
Beven
, 2001)Slide27
(b) Partial area infiltration excess overland flow
P
P
P
q
o
f
Fraction of area contributing to overland flow
(following Beven, 2001)Slide28
(c) Saturation excess overland flow
P
P
P
q
r
q
s
q
o
Variable source area
(following
Beven
, 2001)
See saturation excess runoff generation animation
http://hydrology.neng.usu.edu/RRP/
(
ch
2)Slide29
(d) Subsurface stormflow
P
P
P
q
s
(following
Beven
, 2001)
See subsurface runoff generation animation
http://hydrology.neng.usu.edu/RRP/
(
ch
2)Slide30
The particular runoff process that dominates is place and time dependent Slide31
Water in Soil
Be able to quantify the properties of water held in and flowing through soil (porosity, moisture content, pressure, suction, hydraulic conductivity)Slide32
(from Freeze and Cherry, 1979)
Negative Pressure
Head.
Suction
vs
Moisture contentSlide33
Variation of soil suction head, |
|, and hydraulic conductivity, K, with moisture content.
(from Chow et al, 1988)Slide34
Infiltration and unsaturated flow
Be able to calculate infiltration, infiltration capacity and runoff rates using the methods described in the Rainfall Runoff workbook chapter 5 and
Dingman
chapter 6.
Surface Runoff occurs when surface water input exceeds infiltration capacity. (a) Infiltration rate = rainfall rate which is less than infiltration capacity. (b) Runoff rate = Rainfall intensity – Infiltration capacity. (from Dunne and Leopold, 1978)Slide35
Saturation excess runoff generation mechanism
Water table near surface
Finite volume of water can infiltrate before soil completely saturated
No further infiltration
All further precipitation is runoff
Occurs in lowlands, zones of convergent topography
Partial contributing area concept
Dunne Mechanism
Saturation from BelowSlide36
(a)
(b)
Infiltration excess runoff generation mechanism
Initially dry soil
Suction large at surface
Total head gradient large
Large infiltration capacity
Penetration of moisture from rainfall
Suction reduces
Infiltration capacity reduces
Excess precipitation becomes runoff
Saturation from Above
Horton MechanismSlide37
Moisture content,
0.5
0.4
0.3
0.2
0.1
Depth, z, (cm)
10
20
30
40
t
1
t
2
t
3
t
4
L
Initial moisture content
o
Saturation moisture content
s
equivalent to porosity, n
Green-Ampt model idealization of wetting front penetration into a soil profileSlide38
Infiltrability – Depth ApproximationSlide39
Time
Surface Water Input
Infiltration Capacity
Runoff
RunoffSlide40
Initialize: at t
= 0, F
t = 0
Is f
c
£
w
t
f
c
> w
t
f
c
£
w
t
No ponding at the beginning of the interval. Calculate tentative values
and column 1.
Ponding occurs throughout interval: F
t+
D
t
calculated using infiltration under ponded conditions equations with t
s
=t and F
s
= F
t
.
Column 3.
Ponding starts during the interval. Solve for F
p
from w
t
, column 2.
D
t' = (F
p
-F
t
)/w
t
F
t+
D
t
calculated using infiltration under ponded conditions equations with t
s
=t+
D
t' and F
s
= F
p
. Column 3.
No ponding throughout interval
Increment time t=t+
D
t
Calculate infiltration capacity f
c
from F
t
, column 1 of table.
A
C
B
D
E
Infiltration is f
t
= F
t+
D
t
-F
t
Runoff generated is r
t
= w
t
D
t - f
t
F
GSlide41
Equations for variable surface water input intensity infiltration calculation.