Estimated Peak Streamflows (Excerpt from SIR 20085235)
Peakgageheight data, peakstreamflow data, and estimated flood probabilities from the June flood for 32 USGS streamgages and 3 ungaged locations are presented in tables 3 and 4. The data listed in table 3 have not received final checks as of the date of writing (December 2008) and are considered provisional until published in the USGS “WaterResources Data for the United States” annual report for water year 2008. Table 5 lists the correspondence between flood probability and recurrence intervals for commonly used flood probabilities. New gageheight or streamflow records were set at 21 USGS streamgages. Flood probabilities at the streamgages with record gageheight or streamflow ranged from 0.002 to 0.04 (range based on 95percent confidence intervals). Five streamgages had estimated flood probability ranges of 0.005 or less based on the 95percent confidence intervals (table 3). The Baraboo River peaked at 10 ft above flood stage (National Weather Service, 2008). Some streams rose and fell rapidly beginning on June 7 or soon after (table 3, fig. 5). Large streams took longer to peak; the Rock River at Afton did not peak until June 21, and flooding continued into July (table 3, fig. 5).
The June 2008 flood took on different characteristics in each of the nine severely damaged communities included in this study. At Reedsburg and Rock Springs, flows of the Baraboo River peaked at approximately 11,500 to 12,900 ft3/s in the early hours of June 10 after especially heavy rainfall fell on the watershed upstream from these communities (table 4). Farther downstream and to the east, the Baraboo River at Baraboo peaked 3 days later from additional thunderstorms that hit the eastern part of the watershed harder than the western part upstream from Reedsburg (figs. 1 and 5). The flooding on the Baraboo River likely had flood probabilities of 0.002 or less (table 3). Flooding on the Baraboo River was responsible for unprecedented closures of Interstates 9094 and 39 north of Madison.
The Kickapoo River at the communities of La Farge, Gays Mills, and Steuben rose and fell rapidly from June 8 to June 12 following the weekend rains on June 7–8 (fig. 5; tables 3 and 4). Peak streamflows at La Farge, Gays Mills, and Steuben had flood probabilities of 0.002 to 0.01 (tables 3, 4, and 5). Peak streamflow for Gays Mills was estimated to range from 19,200 ft3/s (rating extrapolation) to 22,000 ft3/s (stepbackwater model, Robert Watson, National Wisconsin Department of Natural Resources, written commun., 2008). Peak streamflow estimates for the Kickapoo River at Gays Mills seem low compared with peak streamflows for La Farge (upstream 22,100 ft3/s) and Steuben (downstream, 28,700 ft3/s); however, comparison of historical peak streamflows of the Kickapoo River from the three streamgages indicate that the peak streamflows can vary from what would be expected based on basin size. Possibly storm tracks and floodplain storage, among other unknown factors, affect peak streamflow relations among the three streamgages. Gage heights for the June 2008 flood peak in La Farge, Gays Mills, and Steuben were 0.9, 1.9, and 4.4 ft higher than the gage heights for the July 1978 flood, respectively (fig. 6, tables 3 and 4; Hughes and others, 1981). For Gays Mills, the June 2008 gage height was approximately 0.3 ft higher than the August 2007 floodpeak gage height (fig. 6).
Farther east, the Crawfish River at Milford rose more slowly than the Kickapoo and Baraboo Rivers and peaked on June 16 after the second set of thunderstorms on June 12 (fig. 5, table 3). The lowlying gentle topography and numerous wetlands in the Crawfish River watershed contributed to the long duration of the flood, which lingered into the latter part of June. Peak streamflow for the Crawfish River likely had a flood probability less than 0.01 (table 3).
The communities of Jefferson, Fort Atkinson, Janesville, and Beloit along the Rock River also experienced prolonged flooding (fig. 5), and the Rock River did not peak until June 21 at Indianford and Afton (table 3). Estimates for flood probabilities for the flooding along the Rock River range widely, from 0.002 to 0.04 (table 3). The extended time for the Rock and Crawfish Rivers flooding resulted in the unprecedented closure of westbound Interstate 94 for June 13–19 between Milwaukee and Madison (Channel 3000, 2008).
Figure5. Hydrographs showing selected USGS streamgages in southern Wisconsin for JuneJuly 2008.
Table 3. Provisional floodpeak gage heights, peak streamflows, and estimated flood probabilities during the June 2008 flood at selected U.S. Geological Survey streamgages in southern Wisconsin.
[The data shown are considered provisional as of the date of publication. Final data will be published in the USGS "Water Resources Data for the United States" annual report for water year 2008. See figure 3 for streamgage locations. Peak of record shown in bold. Estimated flood probability range based on estimates: The flood probability for a particular streamflow is the probability or odds of that streamflow being equaled or exceeded in any given year. For example, a probability of 0.01 means there is a 1 percent chance of that flow magnitude being equaled or exceeded in any given year. Stated another way, the odds are 1 in 100 flow will equal or exceeded that magnitude in any given year. The traditional concept of recurrence interval is directly related to the flood probability. By definition, the recurrence interval corresponding to a particular flood probability is equal to one divided by the flood probability. For example, the flood probability of 0.01 corresponds to the 100year flood. Based on direct comparison of floodpeak discharge to the discharge estimates for various flood probabilities (traditional approach). Estimated flood probability range based on 95percent confidence intervals: Based on comparison of floodpeak discharge to the lower and upper bounds of the 95percent confidence limits for discharge estimates for various flood probabilities (alternative approach). Abbreviations: mi^{2}, square miles; ft^{3}/s, cubic feet per second, yr, year; >, greater than; < less than; n/a not applicable or not available; ND, not determined; e, estimated; P, present; LP3, procedure for calculating flood probabilities by fitting systematic annualpeakdischarge data to a logPearson type III distribution (Interagency Advisory Committee on Water Data, 1982). WIE, flood probabilities calculated using weighting of independent estimates procedure (Interagency Advisory Committee on Water Data, 1982, appendix 8); GIS, used GISbased basin characteristics for regional regression equations used in WIE procedure; Regional regression equations from Walker and Krug (2003)]
USGS
station No. 
Stream and place
of determination 
Drainage
area
(mi^{2}) 
Gage period
of record
(water years) 
Maximum prior to current flood 

Maximum for June 2008 flood 
Date 
Gage height (feet) 
Discharge (ft^{3}/s) 
Date 
Time 
Gage height (feet) 
Discharge (ft^{3}/s) 
Period of record outlier based on LP3 procedure 
Estimated floodprobability range 
Frequency calculation bestfit method 
Based on estimate 
Based on 95percent confidence intervals 
 
04073500 
Fox River at Berlin 
1,340 
1898P 
03171946 
15.50 
6,900 
 06222008 
18:30 
^{1}16.08 
6,080 
 0.040.1 
0.04 
WIE 
04085427 
Manitowoc River at Manitowoc 
526 
197296, 1997P 
03311979 
13.24 
8,280 
 06132008 
05:30 
12.04 
6,100 
 0.040.1 
0.020.1 
WIEGIS 
04086000 
Sheboygan River at Sheboygan 
418 
191624, 1951P 
08061998 
12.02 
7,820 
 06092008 
08:25 
11.08 
6,810 
 0.040.1 
0.040.1 
WIE 
04086500 
Cedar Creek near Cedarburg 
120 
193070,
197481,
198387,
1991P 
03301960 
12.25 
3,600 
 06142008 
09:00 
10.59 
1,880 
 0.10.2 
0.2 
WIE 
04086600 
Milwaukee River near Cedarburg 
607 
1981P 
05232004 
13.11 
5,720 
 06132008 
18:45 
13.98 
6,980 
 0.040.1 
0.0050.04 
WIEGIS 
04087000 
Milwaukee River at Milwaukee 
696 
1914P 
06211997 
10.00 
16,500 
 06072008 
22:00 
8.07 
10,400 
 0.040.1 
0.04 
WIE 
04087204 
Oak Creek at South Milwaukee 
25.0 
1964P 
08061986 
9.88 
1,140 
 06072008 
20:00 
11.56 
2,370 
yes 
<0.002 
0.0020.005 
WIE 
04087220 
Root River near Franklin 
49.2 
1964P 
03301960 
9.57 
5,130 
 06082008 
14:00 
11.00 
5,350 
 0.010.02 
0.0050.02 
LP349% URBAN 
04087233 
Root River Canal near Franklin 
57.0 
1964P 
03041974 
9.88 
1,440 
 06092008 
04:30 
12.13 
1,560 
 0.020.04 
0.010.04 
WIE 
04087240 
Root River at Racine 
190 
1963P 
03051974 
8.54 
4,500 
 06092008 
10:30 
11.29 
8,050 
yes 
<0.002 
0.0020.005 
WIE 
04087257 
Pike River near Racine 
38.5 
1972P 
08202007 
8.24 
1,720 
 06082008 
01:30 
8.97 
1,960 
 0.010.02 
0.0020.04 
LP321% URBAN 
05404116 
South Branch Baraboo River at Hillsboro 
39.1 
1989P 
06291990 
15.60 
4,010 
 06082008 
21:00 
16.12 
14,800 
yes 
0.0050.01 
0.0020.005 
WIEGIS 
05405000 
Baraboo River near Baraboo 
609 
191422, 1943P 
03261917 
17.50 
7,900 
 06132008 
00:30 
27.51 
18,000 
yes 
<0.002 
0.0020.005 
WIE 
05408000 
Kickapoo River at La Farge 
266 
1939P 
07011978 
14.92 
14,300 
 06082008 
23:15 
15.78 
22,100 
yes 
0.0020.005 
0.0020.01 
WIE 
05410490 
Kickapoo River at Steuben 
687 
1933P 
07031978 
14.81 
16,500 
 06102008 
03:15 
19.16 
28,700 
yes 
0.0020.005 
0.0020.01 
WIE 
05413500 
Grant River at Burton 
269 
1935P 
07161950 
24.82 
25,000 
 06132008 
02:45 
23.31 
13,000 
 0.10.2 
0.1 
WIE 
05414000 
Platte River near Rockville 
142 
1935P 
07161950 
17.26 
43,500 
 06122008 
19:30 
e14.17 
e15,200 
 0.020.04 
0.010.04 
WIE 
05423500 
South Branch Rock River at Waupun 
63.6 
194969, 1987P 
04031959 
7.97 
1,500 
 06132008 
08:15 
10.07 
2,360 
 0.0050.01 
0.0020.02 
WIE 
05425500 
Rock River at Watertown 
969 
193270, 1977P 
03311979 
6.19 
5,080 
 06132008 
08:30 
7.81 
7,600 
 0.0020.005 
0.0020.01 
WIE 
05425912 
Beaver Dam River at Beaver Dam 
157 
1985P 
06142004 
10.68 
1,140 
 06162008 
14:45 
^{1,2}845.53 
1,700 
yes 
0.0050.01 
0.0020.02 
LP3REGULATED 
05426000 
Crawfish River at Milford 
762 
1932P 
04061959 
11.15 
6,140 
 06162008 
15:45 
13.59 
7,110 
 0.0020.005 
0.0020.01 
WIE 
05426250 
Bark River near Rome 
122 
1980P 
04201993 
2.56 
476 
 06092008 
01:00 
4.59 
1,370 
yes 
<0.002 
0.0020.005 
WIEGIS 
05427570 
Rock River at Indianford 
2,630 
1975P 
04051979 
16.23 
11,900 
 06212008 
03:00 
18.33 
14,900 
 0.010.02 
0.0020.04 
WIE 
05427718 
Yahara River at Windsor 
73.6 
197681, 1990P 
07061993 
6.58 
2,050 
 06092008 
01:30 
6.97 
3,200 
yes 
0.010.02 
0.0020.04 
WIEGIS 
05429500 
Yahara River at McFarland 
327 
1931P 
04101959 
5.82 
867 
 06142008 
00:15 
7.12 
980 
 0.0020.01 
0.0050.01 
WIEGIS 
05430175 
Yahara River near Fulton 
518 
1977P 
06181996 
11.16 
3,230 
 06142008 
00:45 
9.87 
2,600 
 0.10.2 
0.10.2 
WIEGIS 
05430500 
Rock River at Afton 
3,340 
1914P 
03231929 
11.81 
13,000 
 06212008 
14:00 
13.51 
16,700 
 0.0020.005 
0.0020.01 
WIE 
05431486 
Turtle Creek Carvers Rock Road near Clinton 
199 
1940P 
04211973 
12.85 
16,500 
 06132008 
17:15 
8.54 
2,010 
 >0.2 
>0.2 
WIEGIS 
05433000 
East Br. Pecatonica River near Blanchardville 
221 
193986, 1988P 
02281948 
15.74 
11,700 
 06092008 
23:15 
15.15 
2,540 
 >0.2 
>0.2 
WIE 
05543830 
Fox River at Waukesha 
126 
1963P 
04011960 
8.00 
2,500 
 06092008 
17:45 
8.85 
2,440 
 0.010.02 
0.0050.04 
WIEGIS 
05544200 
Mukwonago river at Mukwonago 
74.1 
1973P 
08222007 
3.96 
317 
 06132008 
04:45 
4.95 
364 
 0.010.02 
0.0050.02 
WIEGIS 
05545750 
Fox River near New Munster 
811 
1940P 
03311960 
9.25 
7,520 
 06152008 
17:45 
^{1}15.18 
5,960 
 0.020.04 
0.020.04 
WIEGIS 
Table 4. Estimated peak gage heights, streamflows, and flood probabilities for selected locations in southern Wisconsin, June 2008 flood.
[Estimated flood probabilities based on regional regression equations from Walker and Krug (2003). Peak flow for given flood probability: The flood probability for a particular streamflow is the probability or odds of that streamflow being equaled or exceeded in any given year. For example, a probability of 0.01 means there is a 1 percent chance of that flow magnitude being equaled or exceeded in any given year. Stated another way, the odds are 1 in 100 flow will equal or exceeded that magnitude in any given year. The traditional concept of recurrence interval is directly related to the flood probability. By definition, the recurrence interval corresponding to a particular flood probability is equal to one divided by the flood probability. For example, the flood probability of 0.01 corresponds to the 100year flood. Abbreviations: USGS, U.S. Geological Survey; mi^{2}, square miles; ft^{3}/s, cubic feet per second; YR, year; <, less than; >, greater than; HWM, highwater mark; NWS National Weather Service; na, not available]
USGS
identification
number 
Stream and
community 
Type
of site 
County 
Drainage
area at site
(mi^{2}) 
Peak flow for given
flood probability (ft^{3}/s) 

Estimated peak flow during June 2008 flood 
0.1 
0.04 
0.02 
0.01 
Date 
Peak gage
height
(feet) 
Estimated
peak flow
(ft^{3}/s) 
Method 
 
None 
Baraboo River at Reedsburg 
No gage data available 
Sauk 
391 
na 
na 
na 
na 
 06/10/2008 
na 
11,50012,500 
Estimated by use of USGS highwatermark data and available stepbackwater hydraulic model extended upstream from Rock Springs. 
05404320 
Baraboo River at Rock Springs 
NWS floodstage forecasting site 
Sauk 
484 
na 
na 
na 
na 
 06/10/2008 
28.7 
12,900 
Estimated by use of available NWS gage height and USGS highwatermark data, slopearea method, and an available stepbackwater hydraulic model. 
05410000 
Kickapoo River at Gays Mills 
NWS floodstage forecasting site, discontinued USGS streamgage 
Crawford 
616.6 
6,740 
8,910 
10,600 
12,500 
 06/09/2008 
20.4 
19,20022,000 
Estimated by use of gage height at NWS floodstage forecasting site, rating extrapolation for discontinued streamgage, and available stepbackwater hydraulic model. 
