1. Macatawa River Watershed: An Overview of Hydrology and Modeling
Dave Fongers
Hydrologic Studies Unit
Land and Water Management Division, MDEQ

2. Overview Hydrology Effect of urbanization Stability concepts Modeling
Hydrologic
Hydraulic
Examples

3. Hydrology: the distribution and movement of water.

4. Watershed
An area contributing runoff and sediment.

5. Watershed
An area contributing runoff and sediment.

6. Hydrograph A plot of flow versus time.

7. 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.

8. Design Storm
24-Hour Precipitation Rainfall Frequency Atlas of the Midwest, Bulletin 71, Midwestern Climate Center, 1992

9. 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.

10. Watershed Size
175 square miles

11. Soils
Soils don’t usually change - possible exceptions: clay caps, significant excavations or fills

12. 1978 Land Use
The most likely cause of hydrologic change.

13. 1997 Land Use
The most likely cause of hydrologic change.

14. 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

15. Curve Numbers
SRO = (P-0.2S)2/(P+0.8S)
S = (1000/CN) - 10

16. Selected Curve Numbers

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

19. Hydrograph for a farm on sandy soil or woods on loamy soil.
Qp=23 cfs V=5 acre-ft.

20. 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.

21. 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.

22. The altered flow regime affects:

23. The altered flow regime affects:
habitat (water velocity, temperature, sediment, other pollutants)

24. The altered flow regime affects:
habitat (water velocity, temperature, sediment, other pollutants)
flooding (frequency and elevation)

25. The altered flow regime affects:
habitat (water velocity, temperature, sediment, other pollutants)
flooding (frequency and elevation)
channel morphology

26. 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

27. 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.

28. 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.

29. Channel-Forming Flow: a theoretical discharge that would result in a channel morphology close to the existing channel.

30. Channel-Forming Flow for Macatawa River

31. Watershed Hydrology Stable? Stream Morphology Stable?
Natural Area
Watershed Hydrology Stable?
Stream Morphology Stable?
Yes
Yes
Classic stable site: natural area, no apparent erosion, good floodplain

32. Mall under development
Watershed Hydrology Stable?
Stream Morphology Stable? No ?
Area transitioning from abandoned farm to mall, the hydrologic characteristics of this area are in transition
Appropriate BMPs can be combined to mimic pre-development runoff characteristics.

33. Watershed Hydrology Stable? Stream Morphology Stable?
Mall
Watershed Hydrology Stable?
Stream Morphology Stable?
Yes ?
Once the mall is built, the area is arguably hydrologically stable, even though the receiving stream can be severely degraded and remain unstable for decades
Although the hydrologic characteristics of this drainage area are stable, past changes may continue to destabilize the receiving stream morphology.

34. Watershed Hydrology Stable? Stream Morphology Stable?
Hager Creek
Watershed Hydrology Stable?
Stream Morphology Stable?
Yes No
A down-cut is an indicator of instability, as is widespread excessive erosion
This is an active down-cut. Stability cannot be determined from one photo however.

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

36. 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

37. 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.
Attempt to restore flow regime

38. Modeling

39. Hydrologic Modeling Hydraulic 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

40. 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

41. Typical Hydrologic Modeling Data
Soils
Land use: historical, current, future
Energy slope of river reaches (can be estimated)
Detention storage-discharge relationship

42. HEC-HMS Model

43. Sample of model results.
100-Year Storm at C&O, No Detention

44. Sample of model results.
100-Year Storm at C&O,
No Detention compared to 2360 Acre-Feet of Detention

45. Typical Hydraulic Modeling Data
Discharge
Representative cross-sections
Manning’s roughness coefficient
Energy slope of river reaches (can be estimated)

46. HEC-RAS Model

47. HEC-RAS Model

48. Examples

49. Pigeon River

50. 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
( cfs/acre)

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

52. Ratios of modeled flow to target flow

53. Target these subbasins
for additional detention

54. Blakeslee Creek 0.32 square mile watershed July 1992 photo
Pre-development conditions existed until 1998
July 1992 photo

55. Blakeslee Creek

56. Blakeslee Creek
CN=47
CN=58
CN=67

57. Blakeslee Creek
CN=47
CN=67
CN=67

58. Predicted 50 percent chance (2-year) flow from calibrated model.
Blakeslee Creek
Watershed Hydrology Stable?
Stream Morphology Stable? No No
Pre-development
Post-development
70% increase in peak flow, 167% increase in runoff volume, former instantaneous peak flow now lasts ~4 hours
Predicted 50 percent chance (2-year) flow from calibrated model.

59. MDEQ Internet Resources
Nonpoint Program
SWQD Guidebook of Best Management Practices for Michigan Watersheds (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

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