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

Provisional Monthly Streamflow Network - Tabular Data: May 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	7,675	5,996	5,325	2,397	11,460	5437500
Rock River near Joslin	9,549	86	10,511	9,504	8,411	3,875	17,910	5446500
Pecatonica River at Freeport	1,326	111	1,049	1,110	900	465	1,977	5435500
Green River near Geneseo	1,003	90	574	1,099	905	304	2,128	5447500
Edwards River near New Boston	445	91	236	574	407	120	1,259	5466500
Kankakee River at Momence	2,294	113	2,602	2,976	2,819	1,468	4,749	5520500
Iroquois River near Chebanse	2,091	103	1,084	2,809	2,229	670	5,534	5526000
Fox River at Dayton	2,642	111	2,761	2,782	2,317	951	5,097	5552500
Vermilion River at Pontiac	579	83	232	792	593	191	1,740	5554500
Spoon River at Seville	1,636	111	811	1,963	1,383	424	4,334	5570000
LaMoine River at Ripley	1,293	105	637	1,571	881	208	3,969	5585000
Bear Creek near Marcelline	349	82	78	430	221	19	911	5495500
Mackinaw River near Congerville	767	81	443	988	835	248	2,142	5567500
Salt Creek near Greenview	1,804	84	1,413	2,483	1,975	624	5,516	5582000
Sangamon River at Monticello	550	116	246	731	531	185	1,637	5572000
So. Fork Sangamon near Rochester	867	76	1,505	1,176	759	158	2,919	5576000
Illinois River at Valley City	26,743	87	32,774	38,367	35,170	15,440	71,880	5586100
Macoupin Creek near Kane	868	98	1,317	1,070	541	86	3,138	5587000
Vermilion River near Danville	1,290	104	860	1,727	1,282	571	3,903	3339000
Kaskaskia River at Vandalia	1,940	55	2,848	2,061	1,585	240	5,202	5592500
Shoal Creek near Breese	735	83	1,861	967	694	105	2,076	5594000
Embarras River at Ste. Marie	1,516	114	3,496	2,017	1,287	380	5,170	3345500
Skillet Fork at Wayne City	464	108	1,082	670	346	38	2,070	3380500
Little Wabash below Clay City	1,131	111	4,959	1,528	870	91	4,670	3379500
Big Muddy at Plumfield	794	55	377	1,498	993	274	4,123	5597000
Cache River at Forman	244	103	51	454	318	27	1,124	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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