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

Provisional Monthly Streamflow Network - Tabular Data: September 2025

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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	3,901	3,349	2,802	1,166	7,026	5437500
Rock River near Joslin	9,549	86	5,117	4,891	4,077	1,784	9,387	5446500
Pecatonica River at Freeport	1,326	111	849	836	679	329	1,467	5435500
Green River near Geneseo	1,003	89	110	372	180	61	1,048	5447500
Edwards River near New Boston	445	91	42	140	53	18	369	5466500
Kankakee River at Momence	2,294	111	944	1,082	830	553	1,945	5520500
Iroquois River near Chebanse	2,091	102	90	586	128	45	1,814	5526000
Fox River at Dayton	2,642	111	876	1,116	755	275	2,673	5552500
Vermilion River at Pontiac	579	83	1	126	18	2	616	5554500
Spoon River at Seville	1,636	111	84	583	201	59	1,380	5570000
LaMoine River at Ripley	1,293	104	28	447	120	26	1,172	5585000
Bear Creek near Marcelline	349	81	1	146	19	1	449	5495500
Mackinaw River near Congerville	767	81	6	222	28	7	646	5567500
Salt Creek near Greenview	1,804	84	146	459	225	122	987	5582000
Sangamon River at Monticello	550	115	1	118	26	8	337	5572000
So. Fork Sangamon near Rochester	867	76	6	176	23	3	456	5576000
Illinois River at Valley City	26,743	87	5,142	12,072	8,224	6,291	24,920	5586100
Macoupin Creek near Kane	868	97	25	204	46	8	498	5587000
Vermilion River near Danville	1,290	104	57	295	113	47	873	3339000
Kaskaskia River at Vandalia	1,940	56	43	552	320	50	1,811	5592500
Shoal Creek near Breese	735	83	38	178	59	12	434	5594000
Embarras River at Ste. Marie	1,516	114	45	349	115	37	1,055	3345500
Skillet Fork at Wayne City	464	107	2	85	19	1	229	3380500
Little Wabash below Clay City	1,131	111	18	232	63	8	826	3379500
Big Muddy at Plumfield	794	55	76	189	108	49	418	5597000
Cache River at Forman	244	103	9	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 2023.

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Streamflow Data

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

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