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

Provisional Monthly Streamflow Network - Tabular Data: August 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	6,320	3,365	2,941	1,280	5,670	5437500
Rock River near Joslin	9,549	86	8,515	5,100	4,361	2,057	9,318	5446500
Pecatonica River at Freeport	1,326	111	1,248	811	673	334	1,516	5435500
Green River near Geneseo	1,003	90	305	396	260	99	1,073	5447500
Edwards River near New Boston	445	91	208	156	85	22	384	5466500
Kankakee River at Momence	2,294	113	1,585	1,151	953	617	1,940	5520500
Iroquois River near Chebanse	2,091	102	436	499	238	64	1,325	5526000
Fox River at Dayton	2,642	111	2,012	1,064	739	317	2,080	5552500
Vermilion River at Pontiac	579	83	100	127	34	8	348	5554500
Spoon River at Seville	1,636	111	503	495	304	80	965	5570000
LaMoine River at Ripley	1,293	104	250	338	194	35	971	5585000
Bear Creek near Marcelline	349	82	27	95	51	1	279	5495500
Mackinaw River near Congerville	767	81	49	161	62	13	397	5567500
Salt Creek near Greenview	1,804	84	408	614	364	163	1,226	5582000
Sangamon River at Monticello	550	116	13	143	49	12	463	5572000
So. Fork Sangamon near Rochester	867	76	44	211	70	6	512	5576000
Illinois River at Valley City	26,743	87	13,522	13,665	11,800	7,619	22,380	5586100
Macoupin Creek near Kane	868	97	111	204	73	14	535	5587000
Vermilion River near Danville	1,290	104	89	389	175	51	1,001	3339000
Kaskaskia River at Vandalia	1,940	56	270	949	841	97	2,122	5592500
Shoal Creek near Breese	735	83	53	216	78	17	664	5594000
Embarras River at Ste. Marie	1,516	114	256	416	193	61	924	3345500
Skillet Fork at Wayne City	464	108	25	151	25	1	483	3380500
Little Wabash below Clay City	1,131	111	169	397	118	18	1,176	3379500
Big Muddy at Plumfield	794	55	214	307	229	56	660	5597000
Cache River at Forman	244	103	30	71	23	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 2023.

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Streamflow Data

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