Macatawa River Watershed: An Overview of Hydrology
and Modeling
Dave FongersHydrologic Studies Unit
Land and Water Management Division, MDEQ517-373-0210
Overview
Hydrology Effect of urbanization Stability concepts Modeling
- Hydrologic
- Hydraulic
- Examples
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.
Design Storm24-HourPrecipitationRainfall Frequency Atlas of
the Midwest, Bulletin 71, Midwestern Climate Center,
1992
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.
Runoff Calculation Methods Rational method
– Widely used for small drainage areas (less than 100 acres)– Most appropriate for paved areas or watersheds with one
uniform land use Curve number and time of concentration methodology
– 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
Development in a watershed can affect the flow regime - increasing total runoff volume and peak flows.
Effects of Urbanization
Loss of infiltration due to development increases total runoff volume and peak flows.
Qp=23 cfs V=5 acre-ft.
Qp=65 cfs V=11 acre-ft.
Qp=90 cfs V=11 acre-ft.
Qp=65 cfs V=11 acre-ft.
Qp=23 cfs V=5 acre-ft.
More rapid runoff further increases peak flows.
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
StabilityHydrology: 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.
Watershed Hydrology Stable?Stream Morphology Stable?
No?
Mall under development
Appropriate BMPs can be combined to mimic pre-development runoff characteristics.
Although the hydrologic characteristics of this drainage area are stable, past changes may continue to destabilize the receiving stream morphology.
Watershed Hydrology Stable?Stream Morphology Stable?
Yes?
Mall
This is an active down-cut. Stability cannot be determined from one photo however.
Watershed Hydrology Stable?Stream Morphology Stable?
YesNo
Hager Creek
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
Goal of Hydrologic Analysisfor NPS Grants to Control Erosion
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.
To estimate the water surface elevation corresponding to a given flow
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
Modeling Software HEC-HMS (Hydrologic Modeling System), HEC-1:
combines and routes discharges from multiple subbasins HEC-RAS (River Analysis System), HEC-2: One-
dimensional 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
100-Year Storm at C&O, No Detention compared to 2360 Acre-Feet of Detention
Sample of model results.
Typical Hydraulic Modeling Data
Discharge Representative cross-sections Manning’s roughness coefficient Energy slope of river reaches (can be
estimated)
Spring Exceedence Curve
4.8 cfs/square mile (0.0075 cfs/acre)
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.
Watershed Hydrology Stable?Stream Morphology Stable?
No Blakeslee CreekNo
Predicted 50 percent chance (2-year) flow from calibrated model.
Pre-development Post-development
MDEQ Internet Resourceswww.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