Hydrologic Analysis for NPS 319 and CMI Grants

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Hydrologic Analysis for NPS 319 and CMI Grants

• Dave Fongers
• Hydrologic Studies Unit
• Land and Water Management Division

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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

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Hydrology the occurrence, distribution, and
movement of water both on and under the earth's
surface.
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• We will focus on surface runoff changes and the
  associated effects on streams.

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• 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.

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

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

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• Hydrograph for a farm on sandy soil or woods on
  loamy soil.

Qp23 cfs V5 acre-ft.
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Loss of infiltration due to development increases
total runoff volume and peak flows.
Qp65 cfs V11 acre-ft.
Qp23 cfs V5 acre-ft.
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More rapid runoff further increases peak flows.
Qp90 cfs V11 acre-ft.
Qp65 cfs V11 acre-ft.
Qp23 cfs V5 acre-ft.
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• The altered flow regime effects

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• The altered flow regime effects
• habitat (water velocity, temperature, sediment,
  other pollutants)

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• The altered flow regime effects
• habitat (water velocity, temperature, sediment,
  other pollutants)
• flooding (frequency and elevation)

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• The altered flow regime effects
• habitat (water velocity, temperature, sediment,
  other pollutants)
• flooding (frequency and elevation)
• channel morphology

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• Channel Morphology the streams 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
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• 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 wont 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

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• 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.

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

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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

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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

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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

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Field Observations

• check for extensive erosion, other causes,
  compare land use, anecdotal information

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Comparison of Aerial Photographs

• Land use changes, stream channel movement

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Gage Analysis
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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.
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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

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Design Storm
24 HourPrecipitationRainfall Frequency Atlas
of the Midwest, Bulletin 71, Midwestern Climate
Center, 1992
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Ease of Water Movement

• Storm sewers, pavement, graded lawns, and bare
  soils collect and convey water more rapidly.

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Delineation - Ryerson Creek
Initial Delineation
Final Delineation 15 area increase
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Soils - Ryerson Creek
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Land Use - Ryerson Creek
Land use comparison
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Ryerson Creek, Holland Drain
Calculated Peak Flows (cfs) 1978 1997 Build-out
50 (2-Year) 26 35 84 10
(10-Year) 67 82 149 1 (100-Year) 143 164 250
Calculated Runoff Volumes (acre-feet) 1978 1997
Build-out 50 (2-Year) 13 24 94 10
(10-Year) 52 74 185 1 (100-Year) 137 176 335
Dramatic increases in runoff volume and peak
flows are predicted for the upper watershed
unless appropriate BMPs are used to compensate
for continuing development.
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Runoff Analysis

• Purposes
• 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

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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

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• 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

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Sample of model results.
100-Year Storm at CO, No Detention
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Sample of model results.
100-Year Storm at CO, No Detention compared to
2360 Acre-Feet of Detention
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Using BMPs to offset hydrologic change

• 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

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Examples
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Pine River
Sometimes the cause of the erosion is obvious.
No further analysis was needed in this case.
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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.
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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.
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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.
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Hager Creek
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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 analysis would be helpful to
verify this.
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Bear Creek
The property owner stated that 30 feet of stream
bank has eroded. Anecdotal observations can be
valuable.
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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.
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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.
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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/re
  ports.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

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• Dave Fongers
• 517-373-0210
• fongersd_at_state.mi.us