Macatawa River Watershed: An Overview of Hydrology and Modeling

Macatawa River Watershed:
An Overview of Hydrology
and Modeling
Dave Fongers
Hydrologic Studies Unit
Land and Water Management Division, MDEQ
517-373-0210
[email protected]
Overview
Hydrology
 Effect of urbanization
 Stability concepts
 Modeling

- Hydrologic
- Hydraulic
- Examples
Hydrology: the distribution and movement of water.
Watershed
An area contributing runoff and sediment.
Watershed
An area contributing runoff and sediment.
Hydrograph
A plot of flow
versus time.
Factors That Affect Discharge





Precipitation
Antecedent
moisture
Snow melt
Frozen ground
Spatial extent of
storm




Ease of runoff
movement (time of
concentration)
Watershed size
(delineation)
Soils
Land use
Human activity
can alter these.
24-Hour
Precipitation
Rainfall Frequency Atlas of
the Midwest, Bulletin 71,
Midwestern Climate Center,
1992
Design Storm
Ease of Water Movement


Time of concentration is the time for runoff to travel from the
hydraulically most distant point of the watershed.
Channelization, addition of drains, storm sewers, pavement,
graded lawns, and bare soils convey water more rapidly.
Watershed Size
175 square miles
Soils
Soils don’t
usually
change possible
exceptions:
clay caps,
significant
excavations
or fills
1978 Land Use
The most
likely cause
of hydrologic
change.
1997 Land Use
The most
likely cause
of hydrologic
change.
Runoff Calculation Methods

Rational method
–
–

Curve number and time of concentration methodology
–
–


Widely used for small drainage areas (less than 100 acres)
Most appropriate for paved areas or watersheds with one
uniform land use
Developed in 1954 by the NRCS, it is the procedure most
frequently used by hydrologists nationwide to estimate
surface runoff from ungaged watersheds
Soil type and land use are combined in a single parameter
that indicates runoff potential
Regression
Drainage area ratio
Curve Numbers
SRO = (P-0.2S)2/(P+0.8S)
S = (1000/CN) - 10
Selected Curve Numbers
Effects of
Urbanization
Development in
a watershed can
affect the flow
regime increasing total
runoff volume
and peak flows.
Hydrograph for a farm on sandy soil or
woods on loamy soil.
Qp=23 cfs V=5 acre-ft.
Loss of infiltration due to development
increases total runoff volume and peak flows.
Qp=65 cfs V=11 acre-ft.
Qp=23 cfs V=5 acre-ft.
More rapid runoff further increases peak flows.
Qp=90 cfs V=11 acre-ft.
Qp=65 cfs V=11 acre-ft.
Qp=23 cfs V=5 acre-ft.
The altered flow regime affects:
The altered flow regime affects:

habitat (water velocity, temperature, sediment,
other pollutants)
The altered flow regime affects:
habitat (water velocity, temperature, sediment,
other pollutants)
 flooding (frequency and elevation)

The altered flow regime affects:
habitat (water velocity, temperature, sediment,
other pollutants)
 flooding (frequency and elevation)
 channel morphology

Channel Morphology: the stream’s form and
structure:
planform (sinuosity): the shape or pattern of the river as
seen from above
 cross-section: the shape of the channel at a specific point
 profile: the slope of the channel, measured at the water
surface or the bottom of the thalweg, the "channel within
the channel," that carries water during low flow conditions

cross-section
planform
Stability
Hydrology: a given set of hydrologic conditions
(antecedent soil moisture, rainfall, snowmelt, etc.)
always cause the runoff from the watershed to
respond in a consistent manner in terms of both
total volume and peak discharge. Practically, this
means the land uses, soils, and drainage patterns
within the watershed are not changing.
Stream or Channel Morphology: the stream's
sinuosity, profile, and cross-sectional dimensions
are constant. This does not mean no erosion. It
does mean no net change in channel shape which
can only occur if the flow regime, especially
channel-forming (1- to 2-year) flow, is not changing.
Past hydrologic changes can cause stream
to be unstable for 60 years or more.
Channel-Forming Flow: a theoretical discharge
that would result in a channel morphology close
to the existing channel.
Extreme flood flows generally have little effect
on channel morphology because they are so
rare. More frequently occurring flows, those
with a 1- to 2-year recurrence interval, are
generally the dominant channel-forming flows in
stable, natural streams (Schueler, 1987 and
Rosgen, 1996). Hydrologic changes that
increase these flows can cause the stream to
become unstable.
Channel-Forming Flow: a theoretical discharge
that would result in a channel morphology close
to the existing channel.
Channel-Forming Flow for Macatawa River
Watershed Hydrology Stable? Yes
Yes
Stream Morphology Stable?
Natural Area
Watershed Hydrology Stable? No
?
Stream Morphology Stable?
Mall under
development
Appropriate BMPs can be combined to mimic
pre-development runoff characteristics.
Watershed Hydrology Stable? Yes
?
Stream Morphology Stable?
Mall
Although the hydrologic characteristics
of this drainage area are stable, past
changes may continue to destabilize
the receiving stream morphology.
Watershed Hydrology Stable? Yes
No
Stream Morphology Stable?
This is an active down-cut.
Stability cannot be determined
from one photo however.
Hager Creek
Stream Instability causes excessive erosion
at many locations throughout a stream reach.
Goal of Hydrologic Analysis
for NPS Grants to Control Erosion
Assess watershed and stream stability so that
proposed solutions will:
 address the cause (improve flow regime)
 not move the problem to another location
 be permanent
General causes of excessive
streambank erosion:






Sparse vegetative cover due to too much animal or
human traffic.
Concentrated runoff adjacent to the streambank, i.e.
gullies, seepage.
An infrequent event, such as an ice jam or low
probability flood, damaging a specific streambank.
Unusually large wave action.
A significant change in the hydrologic response of
the watershed.
A change in the stream form impacting adjacent
portions of the stream, i.e. dredging, channelization.
Modeling
Hydrologic Modeling
 To estimate the peak discharge changes due
to changing hydrology
 To estimate the size and effectiveness of
added detention
 Can not demonstrate river stability, although
may indicate instability
Hydraulic Modeling
 To estimate the water surface elevation
corresponding to a given flow
Modeling Software

HEC-HMS (Hydrologic Modeling System), HEC-1:

combines and routes discharges from multiple subbasins
HEC-RAS (River Analysis System), HEC-2: Onedimensional steady flow water surface profile computations.
TR-55: calculates urban runoff, intended for smaller
watersheds of two to three reaches.
TR-20: similar to TR-55 but for intended for whole basin.

SWMM (StormWater Management Model): single event


and continuous simulations of water quantity and quality,
primarily for urban areas.

Numerous others
Typical Hydrologic Modeling Data




Soils
Land use: historical, current, future
Energy slope of river reaches (can be
estimated)
Detention storage-discharge
relationship
HEC-HMS Model
Sample of model results.
100-Year Storm at C&O,
No Detention
Sample of model results.
100-Year Storm at C&O,
No Detention compared
to 2360 Acre-Feet of
Detention
Typical Hydraulic Modeling Data




Discharge
Representative cross-sections
Manning’s roughness coefficient
Energy slope of river reaches (can be
estimated)
HEC-RAS Model
HEC-RAS Model
Examples
Pigeon River
Spring Exceedence Curve
Paul Seelbach, MDNR, has calculated exceedence curves for
trout streams. For the Pigeon River watershed, hydrologic
modeling was used to compare flows from each subbasin to
4.8 cfs per square mile.
4.8 cfs/square mile
(0.0075 cfs/acre)
Pigeon River has
remained a good
trout stream below
West Olive Street.
Ratios of modeled flow to target flow
Target these subbasins
for additional detention
Blakeslee
Creek
0.32 square mile
watershed
July 1992 photo
Blakeslee
Creek
Blakeslee
Creek
CN=47
CN=58
CN=67
Blakeslee
Creek
CN=47
CN=67
CN=67
Watershed Hydrology Stable? No
No
Stream Morphology Stable?
Pre-development
Blakeslee
Creek
Post-development
Predicted 50 percent chance (2-year) flow from calibrated model.
MDEQ Internet Resources
www.michigan.gov/deq/
• Nonpoint Program
• SWQD Guidebook of Best Management Practices for
Michigan Watersheds. 1992. (Reprinted October 1998.)
• GIS Information
• Stream Stability And Channel Forming Flows. March 2001
• Computing Flood Discharges For Small Ungaged
Watersheds. October 2001
• Hydrologic Impacts Due to Development. Revised June
2001
• Stormwater Management Guidebook. Revised August 1999
• Floodplain Management for Local Officials, Third Edition.
August 1999
“A river is the report card for its watershed.”
Alan Levere, CT DEP