Provisional Monthly Streamflow Network - Data Details, Illinois State Water Survey

Provisional Monthly Streamflow Network - Tabular Data: August 2026

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				Long-term monthly flows for period of record (cfs)
Station	Drainage area (sq. mi.)	Years of record	Monthly mean flow (cfs)	Mean flow*	Median (50% exceedence) flow	90% exceedence flow	10% exceedence flow	USGS Station No.
Rock River at Rockton	6,363	86	3,967	3,399	2,980	1,280	5,760	5437500
Rock River near Joslin	9,549	86	4,743	5,134	4,493	2,057	9,318	5446500
Pecatonica River at Freeport	1,326	111	829	816	673	334	1,516	5435500
Green River near Geneseo	1,003	90	662	395	265	101	1,049	5447500
Edwards River near New Boston	445	91	1,369	156	85	22	384	5466500
Kankakee River at Momence	2,294	112	2,902	1,155	960	617	1,940	5520500
Iroquois River near Chebanse	2,091	103	2,570	498	240	64	1,325	5526000
Fox River at Dayton	2,642	111	2,391	1,073	744	317	2,080	5552500
Vermilion River at Pontiac	579	83	416	126	34	8	348	5554500
Spoon River at Seville	1,636	112	2,982	495	308	80	965	5570000
LaMoine River at Ripley	1,293	105	1,097	337	199	35	971	5585000
Bear Creek near Marcelline	349	81	117	94	51	1	279	5495500
Mackinaw River near Congerville	767	81	1,213	159	61	13	397	5567500
Salt Creek near Greenview	1,804	84	1,898	611	365	163	1,226	5582000
Sangamon River at Monticello	550	117	1,562	142	48	12	463	5572000
So. Fork Sangamon near Rochester	867	77	173	208	68	6	512	5576000
Illinois River at Valley City	26,743	87	30,416	13,663	11,930	7,619	22,380	5586100
Macoupin Creek near Kane	868	98	26	203	76	14	535	5587000
Vermilion River near Danville	1,290	105	4,797	386	174	51	1,001	3339000
Kaskaskia River at Vandalia	1,940	56	1,239	936	745	97	2,122	5592500
Shoal Creek near Breese	735	83	48	214	77	17	664	5594000
Embarras River at Ste. Marie	1,516	114	894	414	194	61	924	3345500
Skillet Fork at Wayne City	464	110	19	150	25	1	472	3380500
Little Wabash below Clay City	1,131	111	250	395	119	18	1,176	3379500
Big Muddy at Plumfield	794	55	107	305	226	56	660	5597000
Cache River at Forman	244	102	27	70	24	4	196	3612000

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Station Numbers are linked to the U.S. Geological Survey, providing more information about each station.

Notes:
Much below normal flow = 90-100% chance of exceedence.
Below normal flow = 70-90% chance of exceedence.
Normal flow = 30-70% chance of exceedence.
Above normal flow = 10-30% chance of exceedence.
Much above normal flow = 0-10% chance of exceedence.
* As reported in U.S. Geological Survey (USGS) Water Resources Data, Illinois, Water Year 2024.

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Streamflow Data

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