33022 - Ivel at Blunham

Grid Reference:	52 (TL) 153 509
Operator:	EA
Catchment Area:	541.3 km²
Level of Station:	18.9 mOD
Max. Altitude:	160.0 mOD
Mean flow:	2.95 m³s^-1
95% exceedance (Q95):	1.03 m³s^-1
10% exceedance (Q10):	5.365 m³s^-1
61-90 Av. Ann. Rainfall:	582 mm

Sample Hydrograph of Gauged Daily Flows

Flow Duration Curve for Gauged Daily Flows

Station Description

Crump profile weir 7.31m wide. Drowning occurs at 0.91m (rating includes drowning correction). Significant bypassing when stage exceeds 1.1m; `truncation' effect evident in annual maxima series. Pre-1966 record of poorer quality. Hydrograph shows influence of u/s mill operation. Effluent from STW has substantial effect on low flows. Many abstractions for spray irrigation. Groundwater abstractions for PWS. One of 3 stations used to calculate Offord flows to determine abstraction regime at Grafham Water.

Catchment Description

The Ivel rises near Hitchin and flows north across Greensand, Chalk and Gault Clays to meet the Great Ouse east of Bedford. 45% superficial deposits, mainly Boulder Clay with some glacial sands and gravels. Predominantly agricultural, with some urban development.

Factors Affecting Runoff

Runoff influenced by groundwater abstraction/recharge.
Runoff increased by effluent returns.
Runoff reduced by industrial/agricultural abstraction.

River Flow and Catchment Rainfall on the National River Flow Archive

Gauged Daily Flows (gdf):	1959 to 2008
Monthly Catchment Rainfall (rnf):	1961 to 2008

Datatype	1950s										1960s										1970s										1980s										1990s										2000s

gdf
rnf

For many stations monthly peak flows are also archived. When daily flow data are not available monthly mean flows may be held on the National River Flow Archive. See Data Holdings for further information.

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