HYDROLOGY September 13, 1999

1
HYDROLOGYSeptember 13, 1999

• Dr. Arthur C. Miller
• Penn State University

2
Outline

• Introductions
• Goals of this Course
• Overview of the Hydrologic Cycle
• Defining a Watershed
• Watershed Reponses
• Modeling the Watershed Response
• Unit Hydrographs
• Precipitation
• Excess Precipitation
• Convolution
• Routing
• Regression Equations
• Wrap-up

3

• Purpose of the Hydrology Course
• Increase participants understanding of the
  Hydrologic Cycle
• Introduce participants to basic terminology and
  concepts of hydrology and hydrologic forecasting
  as applied watershed response.
• Establish the course objectives as per the
  expectations of the participants.

4
In the end, it is intended that participants will
have a better understanding of the hydrologic
response of a watershed, the assumptions in the
process, and the responsibilities associated with
interpreting and issuing a hydrologic analysis.
5
Hydrology

• an earth science. It encompasses the
  occurrence, distribution, movement, and
  properties of the waters of the earth and their
  environmental relationships." (Viessman, Knapp,
  Lewis, Harbaugh, 1977 - Introduction to
  Hydrology, Harper Row Publishers, New York)

6
Units ??
7
Area

• 1 acre 43,560 ft2
• 1 mi2 640 acres
• 1 hectare 100m x 100m 2.471 acres 10,000 m2
• 1 km2 0.386 mi2

Area Volume Runoff
Volume Discharge
8
Volume

• 1 acre-foot 1 ac-ft 1 acre of water x 1 foot
  deep 43,560 x 1 43,560 ft3
• 1 ac-inch 1 acre x 1 inch deep 43,560 x 1/12
  3,630 ft3
• 1 ft3 7.48 gallons
• 1 gallon H2O 8.34 lbs.
• 1 m3

Area Volume Runoff Volume
Discharge
9
Runoff Volume

• 1-inch of runoff over 1 square mile
• 1/12 feet x 1 mi2 x 640 acres/mi2 x 43,560
  ft2/mi2 2,323,200 ft3

Area Volume Runoff Volume
Discharge
10
Discharge

• 1 cfs 1 cubic foot per second
• 1 cfs x 7.48 gal/ft3 x 3600 sec/hr x 24 hrs/day
  646,272 gpd 0.646 MGD
• 1 cfs x 3600 sec/hr x 24 hrs/day 86,400 cfs/day
• 86,400 cfs/day x 1 ac-ft/43,560 ft3 1.983
  ac-ft/day ( 2 ac-ft/day)
• 1.983 ac-ft/day x 12 inches/ft x 1 day/24 hrs
  0.992 ac-in/hr
• 1 ac-in/hr x 43,560 ft3/ac-ft x 1 hr/3600 sec x 1
  ft/12 inches 1.008 cfs

Area Volume Runoff
Volume Discharge
11
Hydrologic Cycle
Topics Precipitation Evaporation Transpiration Sto
rage-surface Infiltration Storage -
Subsurface Runoff Water Movement Streamflow Storag
e-Reservoirs
12
Precipitation

• ... primary "input"
• affected by large scale global patterns,
  mesoscale patterns, "regional" patterns, and
  micro-climates.
• Knowing and understanding the general,
  regional, and local precipitation patterns
  greatly aids forecasters in determining QPF
  values.
• In addition to the quantity of precipitation,
  the spatial and temporal distributions of the
  precipitation have considerable effects on the
  hydrologic response.

Precipitation -Snow Evaporation Transpiration St
orage-surface Infiltration Storage -
Subsurface Runoff Water Movement Streamflow Storag
e-Reservoirs
13
Snow

• ... nature of the modeling efforts that are
  required.
• response mechanisms of snow are at a much
  slower time scale than for most of the other
  forms of precipitation.
• The melt takes place and the runoff is "lagged"
  due to the physical travel processes.
• Items to consider in the snowmelt process are
  the current "state" of the pack and the snow
  water equivalent of the snow pack., as well as
  the melt potential of the current climate
  conditions.
• A rain-on-snow event may produce very high
  runoff rates and is often a difficult situation
  to predict due to the integral nature of the
  runoff and melt processes. The timing of these
  events is often very difficult to predict due to
  the inherent "lag" in the responses.

Precipitation -Snow Evaporation Transpiration St
orage-surface Infiltration Storage -
Subsurface Runoff Water Movement Streamflow Storag
e-Reservoirs
14
Evaporation

• Evaporation is a process that allows water to
  change from its liquid phase to a vapor.
• Hydrologists are mostly interested in the
  evaporation from the free water surface of open
  water or subsurface water exposed via the
  capillary action however, precipitation that is
  intercepted by the vegetative canopy may also be
  evaporated and may be a significant amount in
  terms of the overall hydrologic budget.
• Factors that affect evaporation are
  temperature, humidity and vapor pressure,
  radiation, and wind speed.
• A number of equations are used to estimate
  evaporation. There are also a number of
  published tables and maps providing regional
  estimates of annual evaporation.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
15
Transpiration

• Water may also pass to the atmosphere by being
  "taken up" by plants and passed on through the
  plant surfaces.
• Transpiration varies greatly between plants or
  crops, climates, and seasons.
• Evaporation and transpiration are often
  combined in a term - evapotranspiration.
• In many areas of the country and during certain
  seasons evapotranspiration is a major component
  of the hydrologic budget and a major concern in
  water supply and yield estimates.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
16
Storage - Surface

• ... Storage - Surface is used to describe the
  precipitation that reaches the ground surface
  however, is not available for runoff or
  infiltration.
• It is instead, held in small quantities on the
  surface in areas, such as the leafy matter and
  small depressions.
• In general, surface storage is small and only
  temporary in terms of the overall hydrologic
  budget however, it may have an effect on a
  storm response as it is effectively "filled"
  early on a storm event.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
17
Infiltration

• Soils, depending on current conditions, have a
  capacity or ability to infiltrate precipitation,
  allowing water to move from the surface to the
  subsurface.
• ... "physically based -gt soil porosity, depth
  of soil column, saturation levels, and soil
  moisture.
• The infiltration capacity of the soil column is
  usually expressed in terms of length per time
  (i.e. inches per hour).
• As more water infiltrates, the infiltration
  generally decreases, thus the amount of water
  that can be infiltrated during the latter stages
  of a precipitation event is less than that at the
  beginning of the event.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration -Subsurface Storage -
Subsurface Runoff Water Movement Streamflow Storag
e-Reservoirs
18
Infiltration cont.

• Storms that have high intensity levels may also
  cause excess precipitation because the intensity
  (inches per hour) may exceed the current
  infiltration capacity (inches per hour).
• periods of low rainfall or no rainfall will
  allow the soil to "recover" and increase the
  capacity to infiltrate water.
• Infiltrated water replenishes soil moisture and
  groundwater reservoirs. Infiltrated water may
  also resurface to become surface flow.
• attempt to account for infiltration by
  estimating excess precipitation (the difference
  between precipitation and excess being considered
  infiltration), for example, the Soil Conservation
  Service (SCS) runoff curve number method

Precipitation Evaporation Transpiration Storage-su
rface Infiltration -Subsurface Storage -
Subsurface Runoff Water Movement Streamflow Storag
e-Reservoirs
19
Subsurface Flow
Precipitation Evaporation Transpiration Storage-su
rface Infiltration -Subsurface Storage -
Subsurface Runoff Water Movement Streamflow Storag
e-Reservoirs

• water may move via several paths.
• subsurface flow can be evaporated if there is a
  well maintained transfer mechanism to the
  surface. This is particularly true for areas of
  high ground water table (the free water surface
  of the groundwater) which is within the limits of
  the capillary action or transport abilities.
• Vegetation may also transpire or use the water.
  
• The subsurface flow may also continue to move
  with the groundwater table as a subsurface
  reservoir, which the natural system uses during
  periods of low precipitation.

20
Storage - Subsurface

• The infiltrated water may continue downward in
  the vertical, may move through subsurface layers
  in a horizontal fashion, or a combination of the
  two directions.
• Movement through the subsurface system is much
  slower than the surface and thus there are
  storage delays. The water may also reach an
  aquifer, where it may be stored for a very long
  period of time.
• In the NWS River Forecast System (RFS), the
  subsurface storage is represented by imaginary
  zones or "tanks". These tanks release the stored
  water at a given or calibrated rate. The
  released water from the subsurface zones is added
  to the surface runoff for convolution with the
  unit hydrograph.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
21
Runoff

• runoff will be used to collectively describe
  the precipitation that is not directly
  infiltrated into the groundwater system.
• is generally characterized by overland, gully
  and rill, swale, and channel flows.
• is that portion of a precipitation event that
  "quickly" reaches the stream system. The term
  "quickly" is used with caution as there may be
  great variability in response times for various
  flow mechanisms.
• Runoff producing events are usually thought of
  as those that saturate the soil column or occur
  during a period when the soil is already
  saturated. Thus infiltration is halted or
  limited and excess precipitation occurs. This
  may also occur when the intensity rate of the
  precipitation is greater than the infiltration
  capacity.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
22
Overland Flow
Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement -Overland flow -Gullies and
Rills -Swales -Channel Flow -Stream
Channels Streamflow Storage-Reservoirs

• Overland flow or surface flow is that
  precipitation that either fails to penetrate into
  the soil or that resurfaces at a later point due
  to subsurface conditions.
• often referred to as "sheet" flow.
• for the purposes of this discussion, overland
  flow (sheet and surface flow, as well) is
  considered to be the flow that has not had a
  chance to collect and begin to form gullies,
  rills, swales

23
Overland Flow (cont.)

• will eventually reach defined channels and the
  stream system.
• may also be infiltrated if it reaches an area
  that has the infiltration capacity to do so.
• Overland flow distances are rather limited in
  length - National Engineering Handbook (1972) -
  overland flow will concentrate into gullies in
  less than 100 feet.
• Other (Seybert, Kibler, and White 1993)
  recommend a distance of 100 feet or less.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement -Overland flow -Gullies and
Rills -Swales -Channel Flow -Stream
Channels Streamflow Storage-Reservoirs
24
Gullies Rills
Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement -Overland flow -Gullies and
Rills -Swales -Channel Flow -Stream
Channels Streamflow Storage-Reservoirs

• ... sheet flow or overland flow will soon
  concentrate into gullies and rills in the process
  of flowing towards the stream network. The
  location of these gullies and rills may vary from
  storm to storm, depending on storm patterns,
  intensities, current soil and land use
  conditions.

25
Swales

• swales are of a more constant or permanent
  nature.
• do not vary in location from storm to storm.
• Swales are a natural part of the landscape or
  topography that are often more apparent than
  gullies and rills.
• Flow conditions and behaviors in swales are
  very close to that which is seen in channels.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement -Overland flow -Gullies and
Rills -Swales -Channel Flow -Stream
Channels Streamflow Storage-Reservoirs
26
Channel Flow

• Excess precipitation ultimately reaches the
  stream channel system.
• the stream system is generally more defined, it
  is by no means a constant or permanent entity.
• The stream bed is constantly changing and
  evolving via aggredation and degradation.
• Stream channels convey the waters of the basin
  to the outlet and into the next basin.
• attenuation of the runoff hydrograph takes
  place.
• Stream channel properties (flow properties)
  also vary with the magnitude of the flow.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement -Overland flow -Gullies and
Rills -Swales -Channel Flow -Stream
Channels Streamflow Storage-Reservoirs
27
Stream Channels

• Channels are commonly broken into main channel
  areas and overbank areas.
• overbank areas are often referred to as
  floodplains.
• Stream gaging stations are used to determine
  flows based on elevations in the channel and/or
  floodplain.
• Bank full is often thought of as flood stage
  although more rigorous definitions are more
  applicable as they pertain to human activity and
  potential loss of life and property.
• It is worth noting that the 2-year return
  interval flow is often thought of as "bank-full".

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement -Overland flow -Gullies and
Rills -Swales -Channel Flow -Stream
Channels Streamflow Storage-Reservoirs
28
Streamflow

• in the public eye -gt the most important aspect
  of flooding and hydrology.
• flooding from streams and rivers have the
  greatest potential to impact human property and
  lives although overland flow flooding,
  mudslides, and landslides are often just as
  devastating.
• Subsurface flow also enters the stream
  although in some instances and regions, stream
  channels lose water to the groundwater table -
  regardless, this must be accounted for in the
  modeling of the stream channel.
• Channels also offer a storage mechanism and the
  resulting effect is most often an attenuation of
  the flood hydrograph.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
29
Storage - Reservoirs

• Lakes, reservoirs, structures, etc. are given
  a separate category in the discussion of the
  hydrologic cycle due to the potential impact on
  forecasting procedures and outcomes.
• provide a substantial storage mechanism and
  depending on the intended purpose of the
  structure will have varying impacts on the final
  hydrograph, as well as flooding levels.
• This effect can vary greatly depending on the
  type of reservoir, the outlet configuration, and
  the purpose of the reservoir.

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
30
Storage - Reservoirs (cont.)

• Flood control dams are used to attenuate and
  store potentially destructive runoff events.
• Other structures may adverse effects. For
  example, bridges may cause additional "backwater"
  effects and enhance the level of flooding
  upstream of the bridge.
• a catastrophic failure of a structure often has
  devastating effects on loss of life and property.
  

Precipitation Evaporation Transpiration Storage-su
rface Infiltration Storage - Subsurface Runoff Wat
er Movement Streamflow Storage-Reservoirs
31
The Watershed

• Watershed
• Defining
• Contours
• Topo maps
• Digital Data

• A watershed is an area of land that drains to a
  single outlet and is separated from other
  watersheds by a divide.
• Hydrologic analysis and synthesis focus on the
  watershed.

32
The Watershed

• Watershed
• -drainage area
• -drainage basin
• -sub-basin
• -sub-area
• Defining
• Contours
• Topo maps
• Digital Data
• Characteristics

• Every watershed has a drainage area.
• Related terms drainage basin, sub-basin,
  sub-area.

33
Defining a Watershed

• Watershed
• Defining
• delineation
• Contours
• Topo maps
• Digital Data
• Characteristics

• Defining a watershed is generally referred to as
  delineating the watershed.
• The process involves determining that area within
  which water would drain to a common point.
• It is often easier to visualize the concept by
  pretending the ground surface is impermeable like
  cement.

34
Defining a Watershed

• Watershed
• Defining
• Contours
• Topo maps
• Digital Data
• Characteristics

Contours are lines of constant elevation. Contours
point or curve uphill at stream
crossings. Contours (generally) have constant
spacing.
35
Defining a Watershed

• Watershed
• Defining
• Contours
• Topo maps
• Digital Data
• Characteristics

• At right, the watershed has been delineated,
  using the contours, for the indicated watershed
  outlet.
• The streams/channel sections have also been
  highlighted within the watershed.

Outlet
36
Defining a Watershed

• Watershed
• Defining
• Contours
• Topo maps
• Digital Data
• Characteristics

• The most common form of mapping used for
  delineation are the USGS topographical maps.
• The most common map scale is the 7.5 minute
  124,000 scale.

37
Defining a Watershed

• Watershed
• Defining
• Contours
• Topo maps
• Digital Data
• GIS
• DEMs
• Characteristics

• The use of electronic or digital data and mapping
  has become rather common place in the field of
  hydrology.
• GIS or Geographical Information Systems are used
  to manage, manipulate, and analyze digital data.
• One of the most common GIS data sets is a Digital
  Elevation Models or DEMs.

38
Defining a Watershed

• Watershed
• Defining
• Contours
• Topo maps
• Digital Data
• Characteristics

• There are a VERY large number of watershed
  characteristics and properties that are used in
  various aspects of hydrologic analysis and
  synthesis.
• Many of these characteristics and properties may
  be somewhat ambiguous in nature and difficult to
  measure and/or estimate.
• Some of the more common characteristics are

39
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Climate
• Geomorphology

40
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

Area is measured in units of L2. Typical units
are acres, square miles, hectares, and square
kilometers. A GIS automatically calculates the
area of the watershed as it is delineated. When a
GIS is not used - other methods are used to
determine the area. A plainimeter is a common
tool. The area of the basin is generally thought
of as that area that would or could contribute
runoff to the outlet of the watershed during a
rain event.
41
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

The slope is a watershed parameter that may take
on several meanings. Recall that slope is rise
over run or a measure of the change in elevation
with distance. The slope may be the average slope
of the main channel that drains the outlet. The
slope may be the slope of the watershed as
defined by the change in elevation from the
outlet to the highest point divided by the
distance to that point.
42
A Note on Slopes
DEM Contours (5m) Slopes (gt10)
43
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

Land Use is a critical element in the hydrologic
response of a watershed. The land use may
determine the amount of runoff, the timing of the
runoff, and the quality of the runoff. Land use
may also drive such factors as evaporation,
transpiration, and heat fluxes between the
earths surface and the surrounding
atmosphere. Typical land use classifications may
include forested, agricultural, urban, etc..
There may also be sub-classes of these groups
new growth forest, densely populated urban, row
crops, etc There are a number of electronic land
use data sets or coverages available. A site
visit to the watershed is ALWAYS a good idea.
44
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

Soils are also very important in the overall
hydrologic cycle, as well as the hydrologic
response. Soils have a variety of properties that
are relevant to the hydrologist infiltration,
infiltration capacity, conductivity (horizontal
and vertical), organic,hydrologic soil group,
etc.. County, state, and national soil surveys
are available for most areas of the country.
45
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

The underlying geology has great influences on
the infiltration and the ultimate fate of
infiltrated water. Bedrock and depth to
bedrock, clay layers, etc.. should be
documented. AS an example, limestone areas are
known to have large cracks or openings. These
large openings and cavities allow for high
infiltration rates and storage, which may result
in lower runoff volumes.
46
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

Urbanization is given its own category, even
though it is essentially a land use or land
cover. Urbanization greatly increases the runoff
as the lands natural ability to infiltrate and
retain water has been severely reduced or
eliminated all together. Urbanization not only
increases the volume of runoff, but it also
speeds up the response. This is due to the
rapid channelization of the runoff.
47
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

The presence of water bodies such as lakes,
ponds, dams, and other wetlands may have
significant impact on the response of a
watershed. Water bodies have the effect of
delaying and storing runoff and this the overall
responseis delayed and reduced in timing and peak
flow, respectively. Some water bodies are
man-made and may be controlled or regulated.
48
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

Geomorphology is used to describe the stream
netwrok that drains the watershed. Metrics such
as width, depth, and slope may be
used. Additionally, measurements of sinuosity (a
measure of how windy the streams are), as well
how many streams there are and how far apart they
are may greatly affect the response of a
watershed. Stream density (miles of stream/square
mile or drainage area) is another common metric.
49
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

A very common descriptor of the geomorphology of
a drainage basin is the stream order. One of the
most common methods of defining stream order is
the Horton stream ordering system. In this
system, a first order stream is an unbranched
tributary. Second order streams occur when two
first order streams come together. A third order
stream results from two second order streams, and
so on. When a first and second order stream come
togoether, the result is still a second order
stream.
50
Watershed Characteristics

• Area
• Slope
• Land Use
• Soils
• Geology
• Urbanization
• Water bodies
• Geomorphology

Geomorphology is used to describe the stream
network that drains the watershed. Metrics such
as width, depth, and slope may be
used. Additionally, measurements of sinuosity (a
measure of how windy the streams are), as well
how many streams there are and how far apart they
are may greatly affect the response of a
watershed. Stream density (miles of stream/square
mile or drainage area) is another common metric.
51
The Watershed Response
Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph
52
The Watershed Response
Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph
Establish your GOALS NEEDS Short term gt Event
Model Long Term gt Continuous
53
The Watershed Response
Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph

• Event Model
• A few hours to a few days
• Initial conditions - CRITICAL

• Continuous
• Long Term
• Initial Conditions - maintained?

54
FOCUS
Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph
55
Surface Runoff - recall

• Overland
• Gullies Rills
• Swales
• Stream Channels

Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph
56
Baseflow
Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph

• A slower response
• For subsurface supplies or storage
• Contribution mostly in long term or tail or
  event.
• May be an inflow or outflow!

57
The Runoff Hydrograph
Long Term vs.- Short Infiltration Evapotranspirat
ion Storage Subsurface Flow Surface
Runoff Baseflow The Runoff Hydrograph
58
Streamflow

• in the public eye -gt the most important aspect
  of flooding and hydrology.
• flooding from streams and rivers have the
  greatest potential to impact human property and
  lives although overland flow flooding,
  mudslides, and landslides are often just as
  devastating.
• Subsurface flow also enters the stream
  although in some instances and regions, stream
  channels lose water to the groundwater table -
  regardless, this must be accounted for in the
  modeling of the stream channel.
• Channels also offer a storage mechanism and the
  resulting effect is most often an attenuation of
  the flood hydrograph.

• Long Term vs.- Short Infiltration
• Evapotranspiration
• Storage
• Subsurface Flow
• Surface Runoff
• Baseflow
• The Runoff Hydrograph
• Streamflow
• Rating Curves

59
Rating Curves

• Rating curves establish a relationship between
  depth and the amount of flow in a channel.

• Long Term vs.- Short Infiltration
• Evapotranspiration
• Storage
• Subsurface Flow
• Surface Runoff
• Baseflow
• The Runoff Hydrograph
• Streamflow
• Rating Curves

60
Factors Affecting the Hydrologic Response

• Current Conditions
• Precipitation Patterns
• Land Use
• Channel Changes
• Others..