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

Provisional Monthly Streamflow Network - Tabular Data: September 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	4,603	3,354	2,812	1,166	7,026	5437500
Rock River near Joslin	9,549	86	6,879	4,893	4,078	1,784	9,387	5446500
Pecatonica River at Freeport	1,326	111	1,088	836	689	329	1,467	5435500
Green River near Geneseo	1,003	90	1,126	369	179	65	1,042	5447500
Edwards River near New Boston	445	91	354	139	53	18	369	5466500
Kankakee River at Momence	2,294	112	1,733	1,081	830	553	1,945	5520500
Iroquois River near Chebanse	2,091	103	231	581	126	45	1,814	5526000
Fox River at Dayton	2,642	111	2,959	1,113	764	275	2,673	5552500
Vermilion River at Pontiac	579	83	42	124	17	2	616	5554500
Spoon River at Seville	1,636	112	588	579	198	59	1,380	5570000
LaMoine River at Ripley	1,293	105	212	443	120	26	1,172	5585000
Bear Creek near Marcelline	349	82	29	144	19	1	449	5495500
Mackinaw River near Congerville	767	81	101	220	27	6	646	5567500
Salt Creek near Greenview	1,804	84	370	456	221	122	987	5582000
Sangamon River at Monticello	550	117	111	117	26	7	337	5572000
So. Fork Sangamon near Rochester	867	77	10	174	23	3	456	5576000
Illinois River at Valley City	26,743	87	16,126	11,991	8,221	6,179	24,920	5586100
Macoupin Creek near Kane	868	98	12	202	46	8	498	5587000
Vermilion River near Danville	1,290	105	376	293	113	47	873	3339000
Kaskaskia River at Vandalia	1,940	56	154	543	316	45	1,811	5592500
Shoal Creek near Breese	735	84	30	177	55	12	434	5594000
Embarras River at Ste. Marie	1,516	114	129	346	114	37	1,055	3345500
Skillet Fork at Wayne City	464	109	N/A	84	18	1	229	3380500
Little Wabash below Clay City	1,131	112	41	230	62	8	826	3379500
Big Muddy at Plumfield	794	55	70	187	106	49	418	5597000
Cache River at Forman	244	102	3	55	13	2	183	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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