Figure 1. Principal geographic features of Onondaga County, N.Y., and

location of the Ninemile Creek watershed model area.

EXPLANATION

Model area

Village or City

04240200 Streamflow gage and USGS gage number

Precipitation gage 

Airport

City

of

04240200 Syracuse

Onondaga

Lake 

Camillus

Seneca

River

Cross

Lake

Otisco

Lake

Skaneateles

Lake

04240180

ONONDAGA COUNTY

Ninemile

Creek

76°30' 15'

43°

5 MILES

5 10 KILOMETERS

0

0

Base from U.S. Geological Survey

Digital Line Graph, 1:100,000

43°

7'

30"

42°

52'

30"

NEW

YORK

Onondaga County

and Detailed Area

U.S. Department of the Interior Fact Sheet FS 112-99

U.S. Geological Survey September 1999

Watershed Modeling Approach To Assessing the Hydrologic

Effects of Future Development in the Ninemile Creek Basin,

Onondaga County, New York

Urbanization can alter the hydrology

of a watershed, particularly the

magnitude and frequency of stormrelated flooding. Quantifying changes in

streamflow that result from urbanization

are critical for planning and designing

bridges, culverts, stormwater-drainage

systems, detention basins, and other

stormwater-management facilities.

Because data on storm-runoff volume and

floodflow in specific areas are commonly

unavailable, and future changes in these

flow characteristics that result from

urbanization cannot be measured directly,

planners and engineers have come to rely

on computerized models for this

information.

The Town of Camillus, a suburb of

Syracuse, N.Y., like many suburban

communities, has undergone recent

growth and is expecting continued

residential and commercial development.

Concern over the hydrologic effects of

future development has prompted efforts

to assess the likelihood that (1) flooding

of Ninemile Creek in parts of Camillus

will increase as the amount of pervious

surface area available for infiltration

decreases, and (2) the use of stormwaterdetention basins to mitigate flooding

could worsen flooding whenever the peak

outflow from a basin coincides with the

peak discharge in the receiving stream,

thereby producing a larger peak discharge

than would occur otherwise. In 1996, the

U.S. Geological Survey, in cooperation

with the Town of Camillus, developed a

precipitation-runoff model representing a
2

SIMULATED RUNOFF,

IN INCHES

MONTHLY RUNOFF

20 30 40 50 60 70 80

20

80

30

40

50

60

70

ANNUAL RUNOFF

0 5 10 15 20 25 0

25

5

10

15

20

OBSERVED RUNOFF, IN INCHES

502 505 103 104 105 502

505

103

104

105

OBSERVED VOLUME,

IN CUBIC FEET PER

SECOND-HOUR

SIMULATED VOLUME,

IN CUBIC FEET PER

SECOND-HOUR

OBSERVED PEAK

DISCHARGE, IN CUBIC

FEET PER SECOND

SIMULATED PEAK

DISCHARGE, IN CUBIC

FEET PER SECOND

STORMFLOW VOLUME STORM PEAK DISCHARGE 

20 503 102 10

20 3

503

50

102

502

103

Figure 2. Simulated runoff, volume, and discharge of Ninemile Creek at

Camillus, Onondaga County, N.Y., in relation to observed values,

water years 1988-96.

41.7-mi2 part of the Ninemile Creek watershed

(fig. 1) to assess the timing and magnitude of peak

discharges that could result from future development

and the use of stormwater-detention basins. This fact

sheet describes the results of the model simulations.

Model Selection

Several hydrologic simulations models are

available that offer a range of functionality and

options. Selection of an appropriate model requires

an assessment of the project objectives and the

characteristics of the watershed that is being

simulated. The model chosen for the 1996-98 study

of the Ninemile Creek watershed was the HSPF

(Hydrological Simulation Program Fortran), release

11, developed by the U.S. Environmental Protection

Agency (Bicknell and others, 1993). This model can

incorporate several hydrologic features of the

watershed that were considered important, including

(1) extensive wetlands, (2) ground-water flow to the

carbonate bedrock, and (3) snowmelt runoff; the

model also can simulate water quality if desired in

the future.

Model Development and Calibration

A Geographic Information System (GIS) was

used to compile spatial data on watershed soils,

land use, slope, surficial geology, and bedrock

geology. This information was simplified and

combined to obtain 14 hydrologic response units
3

10

104

DISCHARGE, IN CUBIC

FEET PER SECOND 103

102

SNOW PACK WATER,

IN INCHES

10 20

NOV

30 10

DEC

20 31

1995

10

JAN

20 31 10 

FEB

20 29 10 

MAR

20 31 10

1996

20 30

APR

A. SNOWPACK WATER EQUIVALENT

B. DISCHARGE

Observed

Simulated

Observed air

temperature

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-40

-20

0

20 

40

60

80

AIR TEMPRATURE, IN

DEGREES FAHRENHEIT

Observed

Simulated 

Figure 3. Winter runoff and snowpack buildup and melt at Camillus, N.Y., 1995-96: (A) Simulated and

observed snow-pack water equivalent. and (B) Simulated and observed discharge of Ninemile Creek

(HRU’s), each of which represents a unique

combination of land use, slope, infiltration rate,

and water-storage characteristics.

Calibration, a critical step in the development of

any simulation model, is the process of comparing

simulated streamflows with observed streamflows

over a range of conditions, then adjusting the

values assigned to the model variables until the

discrepancies are minimized. Through the

calibration process, model errors are calculated,

and their effect on the simulation results are

evaluated. Uncalibrated or poorly calibrated

models can produce erroneous or misleading

information and could result in poor planning or

engineering decisions. The correlations between

simulated and observed annual and monthly runoff

for water years 1989-96 (October 1, 1988 through

September 30, 1996) and between simulated and

observed stormflow volumes and peak discharges

for 30 non-winter storms in the Ninemile Creek

watershed are depicted in figure 2.

The annual maximum peak discharge in this area

typically results from combined rainfall and

snowmelt. For example, rain and snowmelt in

January 1996 produced one of the highest recorded

peak flows (2,530 ft3

/s) on Ninemile Creek at

Camillus (fig. 3B); this discharge occurs on average

once every 15 years. This storm also produced the

highest mean daily discharge recorded at the

Camillus stream gaging station (1,690 ft3/s) since the

station began operation in 1958. The simulated

values for this 3-day storm (January 18-20, 1996)

were within 3 percent of the observed peak discharge

and within 10 percent of the runoff volume (fig. 3).
4

OBSERVED

SIMULATED (current conditions)

DEVELOPMENT BUILDUP

 10 percent

 50 percent

 100 percent

EXPLANATION

8 9 10 11 12 13 14 15 16

B. IMPERVIOUS LAND

14 15 16 17 

8 9 10 11 12 13 14 15 16 

A. OPEN/RESIDENTIAL LAND 

70

90

110

130

150

170

190

210

230

250

270

14 15 16 17 0

50

100

150

200

250

300

350

400

450

April 1995 April 1995

July 1996 July 1996

DISCHARGE, IN CUBIC FEET PER SECOND

 Figure 4. Observed and predicted spring and summer stormflows of Ninemile

Creek at Camillus, N.Y. under present conditions and with future development at

10-, 50-, and 100-percent buildup, represented in two ways: A. As open/residential

land, and B. As impervious land.

Effects of Future Development

Possible future development in the Ninemile Creek

watershed was represented in the model in two ways:

(1) as an “open/residential” area that simulates runoff

from mixed pervious and impervious areas that drain

to pervious areas, or (2) as an impervious area that

drains directly to stream channels. Under present-day

conditions, about 7 percent of the modeled area is

developed, about 0.4 percent of which is impervious

land that drains directly to stream channels. An

additional 60 percent of the modeled area is

developable (referred to as “100-percent buildup”

herein). Under this condition about 7 percent of the

model area is considered impervious. The simulations

of potential development reflects current land-use

zoning restrictions and represents only the areas that

are suitable for development; for example, steep

slopes and wetlands were excluded.

Runoff after future development will probably

reflect the increase in open/residential and impervious

lands. The most effective way to represent these

factors in the model is uncertain because future

drainage patterns are unknown, but comparing the

simulated hydrologic effects of development as open/

residential land with the effects of development as

impervious land provides an indication of the

watershed’s probable response to future development.

Examples of the simulated watershed response to

spring and summer storms under the two types of

buildup are plotted in figure 4 and summarized in

table 1.

The simulated effects of both types of development

were most pronounced in the summer, when soilTable 1. Predicted increases in

discharge in Ninemile Creek at

Camillus, N.Y., resulting from future

development as open/residential

land and as impervious land.

 Average percent increase

 in non-winter stormflow

Percent Peak Runoff

Buildup discharge 1 volume

A. Buildup as Open/Residential Land

10 10 1.4

 50 22 5.8

 100 37 11

B. Buildup as Impervious Land

 10 13 2.1

 50 38 7.5

 100 68 13

1

Average increases in relation to calibrated

vales for 30 non-winter 1995-96
5

Figure 5. Simulated 1995-96 peak stormflow of Ninemile Creek at Camillus, N.Y., based on

future development at 10-, 50-, and 100-percent buildup as: A. Open/residential land.

B. Impervious land.

PEAK DISCHARGE IN CUBIC FEET PER SECOND

50

5,000

100

200

500

1,000

2,000

PEAK DISCHARGE,

IN CUBIC FEET PER SECOND

A. OPEN/RESIDENTIAL LAND

50 5,000 100 200 500 1,000

B. IMPERVIOUS LAND

10 percent buildup

50 percent buildup

100 percent buildup

50 5,000 100 200 500 1,000 2,000 2,000

water storage is low, and infiltration occurs readily in

pervious areas. Precipitation during other times of the

year, when soil-water storage is near capacity

(because evapotranspiration is low), does not

infiltrate and produces mostly surface flow; thus, the

effects of increased impervious-surface area are

smaller during these seasons than in the summer.

Increases in peak discharge from large storms were

also less than the increases resulting from small

storms (fig. 5) because large storms deplete soil-water

storage and produce mostly surface flow.

A comparison of log-Pearson Type-III probability

curves (a method used to estimate the magnitude and

frequency of floodflows) for simulations of

development as impervious land indicated that the

increase in peak discharge was about the same for

storms of all magnitudes. Thus, the relative effect of

increased urbanization diminishes with increasing peak

discharge. Analyses of peak discharges for the 1989-96

water years indicate that, under 100-percent buildup as

impervious land, stormflows that now occur on average

once every 2 years will occur once every 1.5 years, and

stormflows that now occur on average once every 5

years will occur once every 3.3 years. Future

development is not expected to cause significant

increases in flooding along Ninemile Creek during

large-magnitude storms but is expected to increase the

frequency and magnitude of flows resulting from small

storms. These simulations also indicated a slight

decrease in discharge of 3-day low flows.

Urbanization also affects three components of

runoff— baseflow (sustained ground-water flow),

interflow (fast-responding ground-water flow), and

surface flow, as indicated in figure 6 for simulations
6

0

50

100

150

200

250

300

350

400

450

500

DISCHARGE, IN CUBIC FEET PER SECOND

14 15 16 17

JULY, 1996

Total runoff Interflow and

baseflow

Simulations as:

 Impervious land

 Open/residential land 

Baseflow

Figure 6. Simulated runoff components of

Ninemile Creek at Camillus, N.Y. for the July 15,

1996 storm, for buildup represented as open/

residential land and as impervious land.

of the July 15, 1996 storm. Baseflow was only

slightly lower in impervious-land simulations

(0.116 in.) than in open/residential-land simulations

(0.118 in.). This small difference is attributed to the

relatively small area (about 7 percent of the

watershed) that would be affected with 100-percent

buildup as impervious land; the decrease in baseflow

would probably be larger, however, in subbasins that

have a relatively large percent increase in impervious

area. Interflow was 74 percent smaller in imperviousland simulations (0.029 in.) than in open/residentialland simulations (0.111 in.), and surface runoff was

about 165 percent greater in impervious-land

simulations (0.114 in.) than in open/residential-land

simulations (0.043 in). Accordingly, the peak

discharges in impervious-land simulations were

larger, and the response to precipitation more rapid,

than in open/residential-land simulations. Flow

component differences between the two types of

simulations diminished as soil-water storage

approached capacity.

Effects of Detention Basins

Stormwater-detention basins are commonly used in

developing areas to attenuate peak discharges and to

control nonpoint-source pollutants. The predicted

effects of a detention basin depend on (1) the storageto-discharge characteristics, (2) the inflow magnitude

relative to available storage, and (3) outflow

magnitude relative to flow in the receiving stream.

Model simulation of the effect of a basin serving a

hypothetical 147-acre moderate-density development

adjacent to Ninemile Creek at Camillus indicate that,

the basin outflow would exceed the uncontrolled flow

that would occur if the basin were absent (fig. 7) for a

period after the peak discharge in Ninemile Creek.

During this period, the difference between the

detention-basin outflow and uncontrolled flow is less

than 1 percent relative to flow in Ninemile Creek at

Camillus. Simulation results for a hypothetical

detention basin with half the original storage capacity

indicated that the difference between basin outflow
7

0

.75

1.5

10

10 2

10 3

10 4

1

0.1

100-year, 24-hour storm

-220

-180

-140

-100

-60

-20

20

DISCHARGE, IN CUBIC

FEET PER SECOND 

0

10

20

30 

40

50

60

DISHARGE, AS A PERCENTAGE

FLOW AT CAMILLUS

BASIN OUTFLOW MINUS UNCONTROLLED

RUNOFF FROM A DEVELOPMENT,

IN CUBIC FEET PER SECOND INCHES

A. PRECIPITATION

B. DISCHARGE OF NINEMILE CREEK

AT CAMILLUS, BASIN OUTFLOW,

AND UNCONTROLLED RUNOFF 

Period of increased downstream flow

Period of decreased downstream flow

EXPLANATION

C. DIFFERENCE BETWEEN BASIN

OUTFLOW AND RUNOFF FROM

DEVELOPMENT 

Basin outflow minus

uncontrolled runoff,

as a percentage of

flow at Camillus

Detention-basin outflow

minus uncontrolled runoff

Ninemile Creek 

at Camillus

Detention-basin outflow

Uncontrolled runoff from

development (no detention)

Figure 7. Predicted flows in Ninemile Creek watershed,

Onondaga County, N.Y., resulting from a 100-year, 24-hour

storm at a hypothetical 147-acre residential development with

and without a stormwater-detention basin . by Phillip J. Zarriello

than would uncontrolled runoff from the

development. Although the increases in peak

discharge that would result from the coincidence of

peak basin outflow with the peak flow in Ninemile

Creek are small, the increases in peak discharge could

be cumulative as new development increase and

stormwater controls are added.

Many parts of the watershed that are expected to

undergo development drain to streams tributary to

Ninemile Creek; channel storage along these

tributaries, particularly those with extensive wetlands,

will decrease and delay peak discharge. Simulations

of a detention basin that drains to a tributary, rather

than directly to Ninemile Creek, indicated no increase

in peak discharge at Camillus under any flow

conditions. The peak outflow from the detention basin

occurred long enough after the peak discharge in the

tributary that the peak flows in Ninemile Creek for

storms of all magnitudes were decreased.

Runoff from the simulated development, which

drains to a tributary, would significantly increase the

peak discharge in the tributary in the absence of a

detention basin. The simulated peak discharge in a

tributary for a 2-year storm was more than twice the

peak discharge under current (undeveloped)

conditions, and the simulated peak from a 100-year

storm was about a third larger. Adding a detention

basin decreased the peak discharge of the tributary

to about the same as that under predevelopment

conditions.

Future Model Applications

The watershed model can help planners and

engineers examine the complexities of runoff and,

thus, support comprehensive stormwater management

decisions in the Ninemile Creek watershed. Ninemile

Creek is believed to be a major source of total

phosphorus to Onondaga Lake (Moffa and others,

1994). Water quality simulations can be added to the

model to help address the magnitude, source, and

control of non-point pollution to Onondaga Lake.

and uncontrolled flow would be about twice as large

as with the full-size basin. Additionally, the maximum

difference between basin outflow and uncontrolled

runoff would occur closer to the time of peak

discharge in Ninemile Creek. As a result, the smaller

basin would contribute about 2 percent more flow to

Ninemile Creek at Camillus near the time of the peak
Place

postage

here

U.S. Geological Survey

Water Resources Division

425 Jordan Road

Troy, New York 12180

Selected References

Bicknell, B.R., Imhoff, J.C., Kittle, J.L., Jr., Donigian,

A.S., and Johanson, R.C., 1993, Hydrological

Simulation Program—Fortran, users manual for

release 10: Athens, Ga., U.S. Environmental

Protection Agency-600/R-93/144, Environmental

Research Laboratory, 660 p.

Moffa, P.E., Nix, S.J., and Dent, S.A., 1994, A watershed

approach to CSO abatement, Onondaga County,

New York: Syracuse, N.Y., Moffa and Associates

Consulting Engineers, Unpublished Report for

Onondaga Lake Management Council, 8 p.

Zarriello, P.J., 1999, A precipitation-runoff model for

part of the Ninemile Creek watershed near Camillus, Onondaga County, New York: U.S. Geological

Survey Water Resources Investigation Report

98-4201, 52 p.

For More Information Contact

Subdistrict Chief

U.S. Geological Survey

30 Brown Road

Ithaca, N.Y. 14850

(607) 266-0217

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286, Federal Center

Denver, Co 80225-0286

This fact sheet and related information can be found

on the world wide web at: http://ny.usgs.gov