Macatawa River Watershed: An Overview of Hydrology

and Modeling

Dave FongersHydrologic Studies Unit

Land and Water Management Division, MDEQ517-373-0210

fongersd@michigan.gov

Overview

Hydrology Effect of urbanization Stability concepts Modeling

- Hydrologic

- Hydraulic

- Examples

Hydrology: the distribution and movement of water.

WatershedAn area contributing runoff and sediment.

WatershedAn 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.

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.

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

– 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

Curve Numbers

S = (1000/CN) - 10SRO = (P-0.2S)2/(P+0.8S)

Selected Curve Numbers

Development in a watershed can affect the flow regime - increasing total runoff volume and peak flows.

Effects of Urbanization

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=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:

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

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.

Channel-Forming Flow for Macatawa River

Watershed Hydrology Stable?Stream Morphology Stable?

YesYes

Natural Area

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

Stream Instability causes excessive erosion at many locations throughout a stream reach.

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.

Modeling

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

HEC-HMS Model

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

Sample of model results.

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

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.

Pigeon River has remained a good trout stream below West Olive Street.

Ratios of modeled flow to target flow

Target these subbasinsfor additional detention

July 1992 photo

0.32 square mile watershed

Blakeslee Creek

Blakeslee Creek

CN=47

CN=58

CN=67

Blakeslee Creek

CN=47

CN=67

CN=67

Blakeslee Creek

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

“A river is the report card for its watershed.”Alan Levere, CT DEP