Hydrologic Analysis for NPS

319 and CMI Grants

Dave Fongers

Hydrologic Studies Unit

Land and Water Management Division

Overview Explanation of hydrology, morphology,

and stability concepts Importance of hydrologic analysis What is expected in a hydrologic report When are BMPs dealing with hydrology

required or encouraged Examples

Hydrology: the occurrence, distribution, and movement of water both on and under the earth's surface.

We will focus on surface runoff changes and the associated effects on streams.

Hydrologic Stability:Condition such that a drainage area maintains an identical response (runoff volume and peak flow) to an identical rainfall over a long time period. This is expected if the land uses, the soils, and the drainage characteristics within the watershed are not changing.

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

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=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 effects:

The altered flow regime effects: habitat (water velocity, temperature, sediment,

other pollutants)

The altered flow regime effects: habitat (water velocity, temperature, sediment,

other pollutants) flooding (frequency and elevation)

The altered flow regime effects: 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

Morphologic or Channel Stability: conditions such that the stream's sinuosity, cross-sectional dimensions, and profile are constant. Because the stream is a dynamic system, this does not mean that the stream won’t move laterally over time, but only that it maintains its characteristics such as bankfull width and width/depth ratio.

This means:• no net change in channel shape and dimensions• stable flow regime, especially channel-forming flow

Channel-Forming Flow: a theoretical, constant 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 1.5 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.

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

Causes of Streambank Erosion Unstable channel morphology

– A significant change in the hydrologic characteristics of the watershed

– A change in the stream form impacting adjacent portions of the stream, i.e. dredging, straightening

Natural river dynamics Large wave action An infrequent event, such as an ice jam or low

probability flood Concentrated runoff adjacent to the streambank Sparse plant cover due to too much foot traffic

Assessing Stream Stability

Stream stability must be assessed so that proposed solutions for erosion problems will:

address the cause be permanent not move an erosion problem to another

location

Stability Indicators Field observations

check for extensive erosion check for other causes of erosion (foot traffic, boat

wakes) compare historical to current land use anecdotal information

Comparison of aerial photos land use changes stream channel movement

Gage analysis Hydrologic study

Field Observationscheck for extensive erosion, other causes, compare land use, anecdotal information

Comparison of Aerial PhotographsLand use changes, stream channel movement

Gage Analysis1.5 Year Recurrence Flows

0%

25%

50%

75%

100%

125%

150%

175%

200%

225%

1920's 1930's 1940's 1950's 1960's 1970's 1980's 1990's

Time (decade)

Pe

r c

en

t o

f 1

.5 y

ea

r fl

ow

s e

xp

ec

ted

Muskegon River,NewagoRiver Raisin,AdrianRiver Raisin,MonroeHuron River, Ann ArborAuSable River,Mio

What is a Hydrologic Study?Analysis of possible changes in the parameters that determine the volume, rate, and timing of surface runoff.

1. Estimate values for applicable parameters.

2. Calculate the impact of identified changes. Modeling and model calibration may be necessary.

3. Evaluate the meaning of the results.

Parameters That Affect Discharge Precipitation Ease of water

movement (time of concentration)

Watershed size (delineation)

Soils Land use

Antecedent moisture

Snow melt Frozen ground Spatial extent of

storm

Design Storm24 HourPrecipitationRainfall Frequency Atlas of

the Midwest, Bulletin 71, Midwestern Climate Center,

1992

Ease of Water MovementStorm sewers, pavement, graded lawns, and bare soils collect and convey water more rapidly.

Initial Delineation

Final Delineation~15% area increase

Delineation - Ryerson Creek

Soils - Ryerson Creek

Land Use - Ryerson Creek

Land use comparison

Ryerson Creek, Holland DrainCalculated Peak Flows (cfs)

1978 1997 Build-out50% (2-Year) 26 35 8410% (10-Year) 67 82 149

1% (100-Year) 143 164 250

Dramatic increases in runoff volume and peak flows are predicted for the upper watershed unless appropriate BMPs are used to compensate for continuing development.

Calculated Runoff Volumes (acre-feet)1978 1997 Build-out

50% (2-Year) 13 24 9410% (10-Year) 52 74 185

1% (100-Year) 137 176 335

Runoff AnalysisPurposes: To estimate changes in discharge

volumes, peaks, and timing due to changing hydrology

To estimate the effectiveness or size of added detention

Cannot demonstrate river stability, although may indicate instability

Runoff Calculation Tools 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

Rational method– widely used for small drainage areas (less than 100 acres)– Most appropriate for paved areas or watersheds with one

uniform land use HEC-HMS

– combines and routes discharges from multiple subbasins Many others

Site-Specific Data Needed: Soils Land use

– historical– current– possibly future

Energy slope and length of river reaches – can be estimated from USGS quadrangles

Detention– volumes– storage-discharge relationship

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.

Unchanged hydrology– maintain and protect existing flow regime

Minor hydrologic change– restore previous flow regime

Past or ongoing change with morphology adapting– balance between improving flow regime and rehabilitating

morphology Ongoing significant change with morphology unstable

and restricted ability to adapt– maintain existing flow regime in future developments,

balance between improving flow regimes from developed sites and rehabilitating morphology

Using BMPs to offset hydrologic change

Examples

Pine River

Sometimes the cause of the erosion is obvious. No further analysis was needed in this case.

Schoolhouse Creek

This outlet of this detention pond did not detain water. No hydrologic study was required since the detention pond was sized for the development.

Plaster Creek

Additional detention was proposed for this site. Field observation indicated that land use had not changed in 22 years. No further hydrologic study was required.

Hager Creek

This unstable stream has extensive erosion all along the banks. The erosion is worse in some areas due to heavy foot traffic. A hydrologic study, incorporating modeling, was conducted to help select the appropriate rehabilitation BMPs.

Hager Creek

Pine River Tributary

This stream may be impacted by increased runoff from new development along the edge of a city, as well as loss of floodplain due to filling. Further hydrologic analysiswould be helpful to verify this.

Bear CreekThe property owner stated that 30 feet of stream bank has eroded. Anecdotal observations can be valuable.

Bear Creek

This erosion may be caused by flow diverting around debris or ice piling against the former bridge supports. Nearby streambanks are stable. Removal of the former bridge supports may eliminate the cause of the erosion at this site.

East Branch AuGres River

This erosion is caused by the diversion of approximately fourteen miles of natural stream through three miles of straight channel. A limited hydrologic study was conducted.

MDEQ Internet Resources• www.deq.state.mi.us/swq/nps/npshome.htm

– Nonpoint Program, SWQD

• www.deq.state.mi.us/lwm/water_mgmt/nps/index.htm

– Nonpoint Program Hydrologic Support, LWMD

• www.deq.state.mi.us/swq/nps/docs1/bmps.htm

– SWQD Guidebook of Best Management Practices for Michigan Watersheds. 1992. (Reprinted October 1998.)

• www.deq.state.mi.us/lwm/water_mgmt/gis/default.asp

– GIS Information, LWMD

• www.deq.state.mi.us/lwm/water_mgmt/Publications/reports.htm

– Stream Stability And Channel Forming Flows

– Computing Flood Discharges For Small Ungaged Watersheds

– Hydrologic Impacts Due to Development. Revised June 2001

– Stormwater Management Guidebook. March 1992

– Floodplain Management for Local Officials, Third Edition. August 1992

Dave Fongers

517-373-0210

fongersd@state.mi.us