RAINFALL - RUNOFF Flashcards
a graph that shows how the flow of water in a river changes over time
HYDROGRAPH
a graphical representation that shows how rivers or streams flow over
time, particularly in response to rainfall
HYDROGRAPH
It is the normal flow of the water at the river
BASE FLOW
the normal or steady contribution of groundwater to the stream. This flow
decreases gradually over time as groundwater levels drop.
BASE FLOW
an increase in river flow due to surface runoff
RISING LIMB
the highest point on the hydrograph, indicating the maximum river
flow during the storm event
when the rate of discharge is greatest
PEAK DISCHARGE
represents the time between the center of the peak precipitation and the
peak discharge. It measures the time it takes for the peak to occur.
LAG TIME
indicates a rapid response of watershed, which means that the peak discharge occurs faster after the rain begins
SHORTER LAG TIME
delays the peak to reach, since they allow
more water to infiltrate the soil or be absorbed by vegetation before reaching the river
LONGER LAG TIME
represents the gradual reduction in river flow as the runoff from the
storm diminishes
FALLING LIMB
when discharge decreases and the ricer level falls
FALLING LIMB
a certain point in which the slope of the hydrograph changes, which indicates that the inflow from the storm has already stopped
and the stored water in the river gradually diminishes
INFLECTION POINT
shows how groundwater levels
gradually decrease back to normal after the storm
RECESSION CURVE
Hydrographs help forecast floods by analyzing
past rainfall and river response. This allows for timely warnings and effective
flood management strategies.
FLOOD PREDICTION MANAGEMENT
Assist in managing water resources by
providing insights into streamflow patterns and water availability. This information
helps in making informed decisions about water allocation for various uses.
WATER RESOURCE MANAGEMENT
Hydrographs are essential for engineering projects
like dams, culverts, and drainage system design. Engineers use them to
determine inflow to reservoirs and to design systems that manage stormwater
effectively, reducing flood risks.
ENGINEERING APPLICATIONS
refers to the process of
dividing a stream flow
hydrograph into its
different components, such
as base flow (water from
groundwater) and direct
runoff (water from
precipitation or snowmelt).
HYDROGRAPH SEPARATION
This method of base flow separation
is the simplest of all three methods.
Separating baseflow using the
_______________ is suitable only
for individual storm events. For
continuous hydrographs, other techniques must be used.
STRAIGHT LINE METHOD
is a simple and common
approach to separating base flow
from direct runoff in a hydrograph.
It assumes that base flow declines at a constant rate during and after
a storm event, and uses a fixed
time interval after the peak flow to
distinguish between base flow and
direct runoff.
FIXED BASED METHOD
(FIXED INTERVAL METHOD)
a
technique used to separate base dlow from direct runoff in a
stream flow hydrograph. The method assumes that
the decline in flow over time is primarily due to base flow, as direct
runoff diminishes quickly after the
peak
RECESSION CURVE METHOD
type of hydrographic method that requires hydrologist to
perform the method,
usually labor intensive
and results are
subjected to individual
hydrologist
interpretation
MANUAL METHOD
A type of hydrographicethod which utilizes computers in
order to eliminate result
subjectivity and reduce
time required for
stream flow record
analysis.
AUTOMATED METHOD
Applications of hydrograph separation
1.Estimation of
groundwater
discharge/
recharge
2. Estimation
of flooding
potential
3. Calibration of model
4. Assessment
of water
development
impacts
represents the direct runoff resulting from 1 cm of effective rainfall
over a drainage area.
UNIT HYDROGRAPH
The ordinates of the direct runoff hydrographs having same time base are directly
proportional to the total amount of direct runoff given by each hydrograph.
PRINCIPLE OF LINEARITY
The hydrograph of direct runoff resulting from a given pattern of effective rainfall will
remain invariable irrespective of its time of occurrence.
PRINCIPLE OF TIME INVARIANCE
The hydrograph of direct runoff resulting from a given pattern of effective rainfall will
remain invariable irrespective of its time of occurrence.
PRINCIPLE OF TIME INVARIANCE
LIMITATIONS
- Not suitable for large or complex basins
- Cannot be used in snow-dominated areas
- Land use changes or basin alterations reduce its accuracy
Advantages
- Requires minimal data
- Useful for quick runoff estimation
- Can be applied in flood forecasting and hydraulic design
For this storm, using __________ or ______________ calculate average
depth of precipitation over the drainage basin.
ISOHYETAL
THIESSEN POLYGON METHOD
Using _________________ of all the available stations plot
mass curves of rainfall for this storm and obtain, average mass curve of
rainfall.
SELF RECORDING RAIN GAUGE DATA (SRRG)
From the average mass curve of rainfallconstruct hyetograph. To construct
hyetograph _____________ during successive units of time are
obtained from the mass curve. The average depths of rainfall per unit of time are then plotted on ordinate against time as __________.
INCREMENTAL RAINFALL QUANTITIES
ABSCISSA
is a widely used method for estimating
the peak runoff (Q) from a watershed or drainage area during a
storm event. It’s commonly applied for small to medium-sized
watersheds and is particularly useful in urban hydrology
RATIONAL FORMULA
Average Discharge of Rainfall Event Formula
Qave = V / T
Rational Formula
Q = CIA
Q = Peak flow (m³/sec)
C = Runoff Coefficient
I = Rainfall Intensity
A = Basin Area (horizontal plane)
is a widely used hydrological tool for estimating direct runoff from
rainfall
A simplified approach that considers rainfall, soil type, land cover,
and antecedent moisture conditions to predict runoff volume.
The method is based on the concept that a portion of rainfall
infiltrates the soil, while the remaining portion becomes runoff.
SOIL CONSERVATION SERVICE (SCS) CURVE NUMBER (CN) METHOD
The _______ value represents the potential for runoff from a specific
watershed, ranging from 0 (no runoff) to 100 (all rainfall becomes
runoff).
CURVE NUMBER (CN)
The maximum amount of
water that can be retained in the soil before runoff occurs.
POTENTIAL MAXIMUM RETENTION (S)
S = (1000/CN) - 10
The amount of water retained in the soil
before runoff begins
ACTUAL RETENTION (Ia)
Ia = 0.2S
Effective Rainfall Formula
Pe = P - la
(rainfall - actual retention)
Estimate Runoff Formula
Q = Pe² / (Pe + s)
