EA Maidenhead level graph -
EA Windsor Park level graph -

Right bank: upstream end of flood prevention channel that comes out below Windsor. Canoe England -

[going upstream above Boulters Lock] the entrance to the upper Jubilee River comes into view almost immediately on the right and is easily identified by a barrier system to only allow canoes and small craft to pass through. The half mile or so tranquil tree lined backwater leads to Taplow Mills where there is no egress and necessitates returning to the Thames.

Gaugemap flow at Taplow The Jubilee River flow

Gaugemap flow at Maidenhead The main river flow

NB zero flow means offline!
Gaugemap flow at Windsor Park The combined flow downstream

Description of the Jubilee River from MWEFAS Operating Procedures (v4)-

The Maidenhead, Windsor and Eton Flood Alleviation Scheme (MWEFAS) was designed to protect the scheme area from flooding up to a flow return period of 1 in 65 years, which equates to a total flow of 515m³/sec (cumecs). The scheme comprises two principal elements:-
i) Jubilee River – a flood relief channel, leaving the River Thames upstream of Boulters Weir and rejoining downstream of Black Potts Viaduct at Datchet. The Jubilee River consists of a 11.6 km long flood relief channel. Levels in the channel are controlled by five weirs, two of which are variable crest, the remaining three being fixed crest weirs. Parts of the Jubilee River have embankments adjacent to the channel in order to provide the necessary flow capacity.
The current capacity of the Jubilee River, maintaining 300mm freeboard, is 145 m³/sec [ NOW UPDATED TO 170 m³/sec - see below ]. The remaining flows are taken down the River Thames and the Maidenhead Ditch.
ii) Cookham and North Maidenhead Defences – A series of flood walls and embankments protecting these areas from overland flood flows. The Cookham floodwalls incorporate moveable flood gates with a drainage system that allows seepage to be pumped from sumps.

Flow Control in the Jubilee River -from Operating version 4 - [updated as indicated]

During the development of, and as a result of, the Public Inquiry into the Maidenhead, Windsor and Eton Flood Alleviation Scheme a commitment was made that the Jubilee River would have its flows strictly controlled through the operation of the gates at Taplow Sluice.
Essentially there are three parts to the commitment, Normal, Low & High flows as detailed below:
Normal Flows
During normal flow conditions (total flow 30 to 190 m³/sec) the Jubilee River will pass a sweetening flow of 10 m³/sec for water quality and environmental purposes.
Low Flows
Following the Public Inquiry a Ministerial Direction was issued which directs how the flows should be split between the River Thames and The Jubilee River for flows up to 40 m³/sec....
When the total Thames flow upstream of the Jubilee River off-take is between 15 and 40 m³/sec, the flow in the Jubilee River should be one third of the total or 10 m³/sec, whichever is the less.
When the total Thames flow upstream of the Jubilee River off-take is between 10 and 15 m³/sec, the flow in the Jubilee River should be maintained at 5 m³/sec.
When the total Thames flow upstream of the Jubilee River off-take is less than 10 m³/sec, flow should be split equally between the Thames and the Jubilee River In the rare circumstances when the total flow is less than 10 m³/sec, the division of flow will be managed actively on a day to day basis taking account of the flow and water quality measurements and quality modelling predictions....
High Flows
To provide flood alleviation flood water will be allowed to pass down the Jubilee River once the flow has reached 180 (one hundred and eighty) m³/sec at Maidenhead Bridge Gauge. In these conditions the existing flow in the Jubilee River will be 10 m³/sec, with approximately 1 m³/sec flowing in the Maidenhead Ditch, so the total system flow will be approximately 191 m³/sec. At this flow the Thames weirs will have been fully drawn.
The current assessment of the capacity of the Jubilee River, maintaining a minimum of 300mm freeboard, is 145 m³/sec.
[Now updated to 170 m³/sec - see below ]
The Taplow Sluices will be operated to ensure that this flow is not exceeded.
The required method of operation on a rising flood is to increase the flow of the Jubilee River in steps of approximately 20 m³/sec to 100 m³/sec, 10 cumec steps to 140 m³/sec and a final 5 cumec step up to a maximum of 145 m³/sec, its current estimated capacity.
[ This is now updated to a maximum of 170 m³/sec with "smaller increments near the peak" ]
On a falling flood, the reductions in flow in the Jubilee River should comprise the same steps in reverse order.
The maximum flow that will be permitted down the Jubilee River will be 145 [now 170] m³/sec. At this discharge the flow within the channel is expected to remain within banks with a minimum of 300mm. The operating arrangements for Taplow Sluice are specifically designed so as to achieve this condition.

Updating -

Maidenhead Windsor and Eton Flood Alleviation Scheme (MWEFAS) Operating Procedures
The Environment Agency has recently published an updated version of the MWEFAS Operating Procedures. There is a significant change in the new operating rules in that the current assessment of the capacity of the Jubilee River, maintaining a minimum of 300m freeboard, has now been increased to 170 m³/sec (from 145 m³/sec). The operating rules have been amended to allow a maximum flow of 170 m³/sec to be diverted into the Jubilee River.
The trigger level, at which the diversion of flow into the Jubilee River will commence, remains the same (when the combined flow in the Jubilee River at Taplow and The River Thames at Maidenhead has reached 190 m³/sec). The manner in which flows will be diverted into the Jubilee River remains similar, i.e. initially in 20 m³/sec increments, and then in smaller increments as the capacity of the Jubilee River is approached.
The updated Operating Rules relating to the diversion of flows into the Jubilee River are similar to the rules that were in place in January 2003, the ‘trigger’ level being the same and the initial diversion of flows in 20 cumces increments also being the same. The diversion of flows in smaller increments near the peak, and the assessment of peak capacity are however new.