OAEA
*T I M
TIME OF TRAVEL STUDIES: AVERAGE AND HIGH FLOWS RIVER OCK
Miss V Johnson
Consultancy Services AEA Technology 1 7 ^ 364 Harwell, Didcot
Oxfordshire 0X11 ORA E n v i r o n m e n t Ag e n c y
DATE DUE NATIONAL LIBRARY & 23 AUG 2000 INFORMATION SERVICE
HEAD OFFICE
Rio House, Waterside Drive. Aztec West, Almondsbury, Bristol BS32 4UD
May 1993
D*mco, Inc 38-293
_ AGENCY
052190
Time of Travel Studies: Average and High Flows for the River Ock
Table showing the velocity of the tracer for each stretch at average and high flows and for average and peak arrival time
1 1 ! 1 | Reach j Average Flow Conditions High Flow Conditions ; 1 t I i < i 1 1 i i | From TO Reach | Peak Average Velocity of Tracer Velocity of Tracer Peak Average Velocity of Tracer J Velocity of Tracer j 1 Length | Arrival Arrival at Peak Arrival Time at Average Arrival Time Arrival Arrival at Peak Arrival Time at Average Arrival Time | 1 (km) | Time Time , (cm/s) (cm/s) Time Time (cm/s) ' (cm/s) 1 1 'I i i * ' | (mins) (mins) (mins) (mins) 1 1 1 1 :i ! : i 1 ! 1 :l 1 1 ! | 1 1 ! 1 | Wantage STW East Hanney ll 36 | 79 81 28.69 27. 98 71 73 31.92 | 31.05 | I 1 1 j East Hanney Venn Mill 3.70 | 227 229 27.17 26.93 235 236 26.24 25.91 | 1 1 1 1 I ! | Venn Mill Marcham 3' 10 | 262 266 19.72 19.42 245 247 21.09 j 20.92 | 1 1 1 I 1 1 | Marcham R .Thames 4 .79 | 449 452 17.78 17.66 318 315 25.10 | 25.34 | I 1 1 1 1 Time of Travel Studies: Average and High Flows for the River Ock
Table showing the velocity of the tracer for each stretch at average and high flows and for average and peak arrival time
i1 1 1 | Reach Average Flow Conditions High Flow Conditions 1 i 1 1 1 | From TO Reach Velocity of Tracer Velocity of Tracer Velocity of Tracer Velocity of Tracer j
1 Length at Peak Arrival Time at Average Arrival Time at Peak Arrival Time at Average Arrival Time | 1 (km) (cm/s) (cm/s) (cm/s) (cm/s) j 1 1 1 1 1 1 1 1 | Wantage STW East Hanney 1.36 28.69 27.98 31.92 31.05 | 1 1 1 1 | East Hanney Venn Mill 3 .70 27.17 26.93 26 .24 25.91 | I 1 1 1 | Venn Mill Marcham 3.10 19.72 19.42 21.09 20.92 |
1 1 | Marcham R. Thames 4 .79 17.78 17.66 25 .10 25.34 |
1 1 1 - ...... 1 Time of Travel Studies: Average and High Flows for the River Ock
Table showing the velocity of the tracer for each stretch at average and high flows and for average and peak arrival time
1 1 | Reach ;1 Average Flow Conditions High Flow Conditions 1 i , 1 1 1 ■ , ' ] From TO Reach (| Peak Average Velocity of Tracer Velocity of Tracer Peak Average Velocity of Tracer ' Velocity of Tracer | 1 Length ’J Arrival Arrival at Peak Arrival Time at Average Arrival Time Arrival Arrival at Peak Arrival Time at Average Arrival Time | 1 (km) | Time Time ^cm/s) (cm/s) Time Time (cm/s) ' (cm/s) ! | :i 1 | (mins) (mins) (mins) (tnins) ) i '1 i : !
1 1 1 ■ 1 1 1 : i | Wantage STW Bast Hanney 1.36 | 79 81 28.69 27.98 71 73 31. 92 | 31.05 | 1 I 1 1 | East Hanney Venn Mill 3.70 | 227 229 27.17 26.93 235 238 26.24 | 25.91 | 1 1 I , 1 1 1 | | Venn Mill Marcham 3.10 | 262 266 19.72 19.42 245 247 21.09 [ 20.92 | i i 1 1 1 1 | Marcham R .Thames 4 .79 j 449 452 17.78 17.66 318 315 25.10 | 25.34 | .i 1 i 1 1 1 1 1 I Time of Travel Studies:1 Average and High Flows for the River Ock
Table showing the velocity of,the tracer for each stretch at average and high flows and for average and peak arrival time
1 1 • | Reach Average Flow Conditions High Flow Conditions 1 1 1 '1 | From To Reach Velocity of Tracer Velocity of Tracer Velocity of Tracer Velocity of Tracer |
1 Length at Peak Arrival Time at Average Arrival Time at Peak Arrival Time at Average Arrival Time | 1 (km) {cm/s> (cm/s) (cm/s) (cm/s) | 1 1 1 1 1 1 1 1 | Wantage STW Bast Hanney 1.36 28.69 27.98 31.92 31. 05 | 1 'i 1 1 J East Hanney Venn Mill 3 .70 27.17 26. 93 26 .24 25. 91 | 1 1 1 1 | Venn Mill Marcham 3.10 19.72 19.42 21.09 20. 92 | ;i i 1 1 1 | Marcham R.Thames 1 4 .|79 17.78 17.66 25.10 25. 34 |
1 1 ) 1 - ...... 1 Time of Travel Studies: Average and High Flows for the River Ock f
Table showing the velocity of the1 tracer for each stretch at average and high flows and Cor average and peak arrival time I
I ! : i * | Reach | Average Flow Conditions High Flow Conditions ' ! ■ ! 1 1 ' ^ | From To Reach | Peak Average Velocity of Tracer Velocity of Tracer Peak Average Velocity of Tracer Velocity of Tracer | Length | Arrival Arrival at Peak Arrival Time at Average Arrival Time Arrival Arrival at Peak Arrival Time at Average Arrival Time | (km)' |'Time Time (cm/s) (cm/s) Time Time (cm/a) (cm/s) , I 1 1 j1(mins) (mins) (mins) (mins) •* ! : 1 11 i
i : ' : 1 ' | Wantage STW East Hanney 1.36 ) 79 SI 28.69 27. 9B 71 73 31.92 1 31.05 | 1 1 1 | East Hanney Venn Mill 3 .70 ) 227 229 27.17 2S.93 235 238 26.24 , 25.91 | t 1 ( Venn Mill Marcham 3.10 j 262 266 19.72 19.42 245 247 21.09 j 20.92 | 1 1 , 1 ( | Marcham R .Thames 4.79 | 449 452 17.78 17.66 310 315 25.10 | 25.34 |
1 ■ 1 I ■ ! Time of Travel Studies: Average and High Flows for the River Ock
; i ( Table showing the velocity of‘the tracer for each (Stretch at average and high flows and for average and peak arrival time
1 1 1 | Reach - Average Flow Conditions High Flow Conditions 1 i 1 1 1 | Prom to ; Reach Velocity of Tracer Velocity of Tracer Velocity of Tracer Velocity of Tracer | 1 > Length at Peak Arrival Time at Average Arrival Time at Peak Arrival Time at Average Arrival Time | ■[ (km) (cm/s) ! (cm/s) (cm/s) < cm/s) | 1 i. 1 1 1 1 1 1 1 1 | wantage STVJ East Hanney 1 36 28.69 27. 98 31.92 31.05 | i 1 1 1 :l | East Hanney Venn Mill 3 70 27.17 26.93 26.24 25.91 [ i I I 1 | Venn Mill Marcham 3 10 19.72 ' 19.42 21.09 20.92 | I 1 1 [ Marcham R.Thames 4 79 17.78 17.66 25.10 25.34 | t 1 1 1 ■ v ' y
Table of Contents
1 Introduction...... I
2 Technical Details...... 1 2.1 Tracer Release Protocol...... 1 2.2 Tracer Sampling Protocol...... 2
3 Notes on the reaches...... 2 3.1 East Hanney...... 2 3.2 Venn M ill...... ,...... 2 3.3 Marcham...... 3 ' 3 7 4 ^ '.Trrrrrrr.' rrr-. tt." r.
4 Results of the Time of Travel Study...... 4
5 Conclusion...... 6
Map showing the location of rivers, sampling points, sewage treatment works and reaches used in the Ock time of travel study.
Sampling point National Sewage River Reach used Key: (Number represents Grid Treatment in time of the last two Reference Work travel study numbers in URN i.e. POCR.OOO8) i i Kingston Bagpuize 90 ; - a 08 STW i (2700) i & 1 Introduction
This report was prepared by Consultancy Services, AEA Technology, and addresses NRA's requirement to measure the 'time of travel' for both average and high flow conditions in specified reaches of the River Ock.
Rhodamine WT was used as a tracer in-determining water's travel time, in terms of the time of first arrival, peak arrival time and the average time for a labelled plume to pass specified reaches of the River Ock. The results are based on measurements made during the dry period 3rd to 11th March 1993 for the average flow, when there had been little rainfall since the very wet January. The measurements involving high flow conditions were made on the 15th and 16th of April after a very wet Easter. The dates for carrying out the.studies were agreed with the NRA.
2 Technical Details
2.1 Tracer Release Protocol
A solution of Rhodamine WT in 10 litres of water was introduced into the river at mid stream and/or where maximum turbulence existed. To ensure a rapid mix this was done by emptying the container within a very few seconds.
The amount of tracer that needs to be added depends upon the potential dispersion of the dye between release and sampling point, the concentration on sampling having to be high enough to give a clear definition of the first and the peak arrival of the tracer. We assumed the length of dispersion to be 10% or more of the travel distance, and thus the amount of tracer used in each measurement was based on a volume of diluting water that allowed a dispersion of 10% of the travel distance, aiming at a concentration of tracer on sampling of maximum 20 ppb. For this purpose, the mean depth and width was estimated by wading the river at the measuring points. The dilution of the tracer by confluence to other water courses further downstream, and the additional dilution that takes place at the confluence to the River Thames at Abingdon, ensured a concentration of Rhodamine WT below drinking water standard in the River Thames.
1 2.2 Tracer Sampling Protocol
The reaches assessed were listed in table 4 of the Tender Document and are shown in table 1. A separate addition of tracer was made for each fetch. At each measuring point water was sampled and monitored for presence of Rhodamine WT. The water was collected midstream or where the flow rate was highest to ensure that the exact time for the first arrival of the tracer was measured. Sampling was from 0.15m below the water surface at a rate of 18 1/min, and a subsample was then removed at a rate of 7ml/min and fed through a flow cell positioned in the spectro fluorimeter sample compartment and continuously analysed for presence of Rhodamine WT. The system is illustrated in figure 1. -T
The spectro fluorimeter was calibrated by filling the flow cell with a solution of 40 ppb Rhodamine WT. The out put from the fluorimeter was recorded every 15 seconds on a data logger, and a chart recorder was used to allow the operators to monitor the progress of the measurement.
3 Notes on the reaches
3.1 East Hannev
The reach being assessed is Letcombe Brook from Above Wantage STW to the Weir Farm at East Hanney. The tracer was added from a bridge at grid reference SU407 916, and sampled at the bridge in front of the Weir Farm in East Hanney, grid reference SU413 926, figure 2.
3.2 Venn Mill
The reach being assessed is the Letcombe brook from Weir Farm, East Hanney and then Childrey Brook to Venn Mill, grid reference SU430 949. The tracer release point was the same as the tracer sampling point at East Hanney. At Venn Mill the Childrey Brook splits in two parts, of which one takes most of the water round the Mill, as illustrated in figure 3. This results from a recent manmade blockage ensuring that not much water is arriving at the mill. At first, sampling was carried out at the bridge at the mill itself, but about 60 meters fiirther down stream in the garden of The Mill House another blockage appears. This second blockage resulted in the failure of live attempted measurements, when tracer was added at Venn Mill for sampling at
2 Marcham, see also section 3.3. The major water course joins the mill stream again just after the blockage and as the two water courses are only about 40 metres apart, sampling was done from the bridge over the major water course. This also allowed the sampling point at Venn Mill to be identical to the release point of the tracer to be sampled at Marcham.
There appears to be a misprint in table 4 of the Tender Document, as the Ordnance Survey map Landranger 164 shows the reach to have a length of 3.7 km rather than"' the 4.76 km stated in the table.
It was noticed that the water level on the 16th of Aprikwas no higher than the level on the 11th of March.
3.3 Marcham
The tracer to be sampled at Marcham was added at the same spot as sampling took place at Venn Mill, where it flowed along the Childrey Brook towards Mill Road, Marcham. It was sampled at the bridge, grid reference SU457 953. The travel distance given in table 4 of the Tender Document is stated to be 2.20 km but appears from the Ordnance Survey map Landranger 164 to have a length of nearer 3.1 km.
Initially we planned to send the tracer from the mill itself. However two attempts were unsuccessful as the tracer never appeared at Marcham, and by walking along all the reach a blockage found in the garden of the Venn Mill House, see also section 3.2. This blockage allowed only a very small amount of water to pass at a time and the large delay time plus the large amount of water coming from the water course led round Venn Mill implied a huge and unpredictable dilution. Therefore, in the successful study, tracer was added from the bridge wall into water that leads past the Mill, see figure 3.
Figure 4 illustrates the water ways near Marcham Mill (source NRA).
3.4 Abingdon
Childrey Brook joins to the River Ock just east of Marcham Mill. The tracer to be measured in Abingdon was, as arranged with the NRA, added in that confluence, grid reference SU458 953. There is an overflow facility between Sandford Brook and River Ock behind the brewery in Abingdon. There was hardly any overflow on the 3rd of
3 March, but an overflow of 8 to 10 cm in height was noticed on the 15th of April. No cross flow was noticed at the flow control arrangement near to the Tesco car park on any of the surveying days. The sampling point was midstream of the River Ock at the Old Iron Bridge at the confluence to River Thames, grid reference SU496 967.
4 Results of the Time of Travel Study
River water was successfully sampled and analysed continuously for Rhodamine WT at all four measuring points. In the associated figures the presence of Rhodamine WT is shown as a voltage deflection on the spectro fluorimeter against time in minutes after the tracer was injected. The cut-off time is the time corresponding to 10% of the Rhodamine WT peak concentration. The deflection given by a known standard solution is also shown, so that the actual concentration figure can be estimated by comparison.
Figure 5 to 9 show the results gathered during average flow conditions while figure 10 to 13 show the result gathered during high flow conditions. As there was a power cut to the data logger the deflection of a standard solution is not shown in figure 8 but in figure 9 from the back-up chart recorder. Here the 40 ppb standard solution gave a deflection of 9.4 on the chart paper scale. The cut-off time for the reach Marcham to confluence to River Thames was also estimated from this chart.
The data for 'first arrival time', 'peak arrival time' and 'average travel time' for each plume to pass the individual reaches is shown in table 1. The 'cut-off time' is also shown. This is defined as the time corresponding to 10% of the peak concentration. This data is used in the calculation of the 'average travel time'. The latter is defined as the time when the half of the dye has past a reach (or the time corresponding to the half of the area below the distribution curve). The area below the curve is calculated using 'first arrival time' and 'cut-off time* as time limits, and the 'average travel time' can then be found as the time corresponding to the half of the area. These calculations can be found on the floppy disk together with the raw data.
Two values are given for the 'first arrival time' of the reach Venn Mill to Marcham on the 16th of April. This is due to a small increase of the deflection after 197 minutes. After a little while the deflection was again back to background and did not rise until 209 minutes after the tracer was injected.
4 It is noticeable that the time of travel from Hast Hanney to Venn Mill was shorter during the average flow period than during high flow. As the water level at Venn Mill was approximately similar on the two surveying days, the times of travel were also expected to be similar. The longer travel time during high flow conditions could be due to delay somewhere on the reach caused by an object (e.g. part of a tree, a trolley etc.) 'fallen' into the river after the first study was carried out.
Table 1 also shows the flow measurements for the River Ock at Abingdon on the dates of the survey. These data are supplied by the RNA. Further more, table 1 shows the quantity of a 20% Rhodamine WT solution (i.e. 200g Rhodamine WT per litre solution) used for each reach. The amount in millilitre Atfas added to a 10 litre container and mixed with water before injection to the river.
Reach Date Mean discharge First arrival Peak arrival Average Cut-off 20% Rhodamine Flow at Abingdon time time travel time time W T consumption conditions (cumecs) (minutes) (minutes) (minutes) (minutes) (ml) Wantage STW 04/03/93 1.320 67 79 81 103 35 to East Hanney Average East Hanney 11/03/93 1.290 199 227 229 265 150 to Venn Mill Average Venn Mill 11/03/93 1.290 225 262 266 308 130 to Marcham Average Marcham to River 03/03/93 1.390 379 449 452 536 200 Thames.Abingdon Average Wantage STW 15/04/93 2.220 58 71 73 95 60 to East Hanney High East Hanney 16/04/93 1.960 203 235 238 272 180 to Venn Mill High Venn Mill 16/04/93 1.960 197? 245 247 283 180 to Marcham High 209? Marcham to River 15/04/93 2.220 244 318 315 380 400 Thames.Abingdon High
Table 1 The data for ’first arrival time\ ’peak arrival time' and 'average travel time’ for a plume to pass the individual reaches durinz averape-and high-flow-conditions. -
5 5 Conclusion
The principal results from time of travel studies at average and high flows in the River Ock are summarised in Table 1. There was about a 30% reduction in travel time for the Marcham to Abingdon reach at high flow in comparison to average flow. The reduction in travel time at high flow for the upstream reaches was only about 6 to 11%, and one reach showed a small increase in travel time.
The different response to the weather conditions in the upstream reaches compared to the Marcham to Abingdon reach is mainly explained by the difference in geology. A greater infiltration of rainwater in the up stream'chalk areas decrease the quantity of run-off from the catchment that feeds the Letcombe Brook, in comparison to the quantity of run-off from the clay catchments of the other tributaries.
The increased time of travel from East Hanney to Venn Mill at normally high flow may perhaps have been due to water backed up by a local blockage somewhere on the reach, but there is no confirmatory evidence.
6 I
car battery
V
'back to river
Figure 1 Instrumental system for on-line analysis of Rhodanwie WT concentration.
Figure 2 Sampling and release point at East Hanney. roajorflow confluence to minor flow
blockage of river
bridge wall
sampling point and release point for downstream study
blockage for leading major flow round the mill
m ajor flow
Figure 3 Sampling and release point at Venn Mill and flow conditions. Figure 4 The water ways near Marcham Mill. The sampling point was at the bridge , while the fracer was added at the confluence of the Childrey Brook to the River Ock. voltage (mV) Hanney. The distrib ution carve fo r the Rhodamine WT is shown with a 40 40 ppb a with shown is WT Rhodamine the r fo carve ution distrib The Hanney. standard solution allowing the actual Rhodamine WT concentration in the river to be to river the in concentration WT Rhodamine actual the allowing solution standard estimated. Figure 5 Figure Time of Travel Study of the reach Abovethe of HanneyEastStudy WantagetoSTW Travel of Time Average flow : Time o f travel study o f the reach Above Wantage STW to East to STW Wantage Above f thereach o study f travel o Time : flow Average Average traveltime Average Time since tracer injected (minutes) injected tracer since Time AVERAGE FLOWAVERAGE 04/03/93 Cut-off time Cut-off 125 40 ppb 40 standard, 135
145
AVERAGE FLOW Time ot Travel Study of the reach East Hanney to Venn Mill
Time since tracer injected (minutes)
Figure 6 Average flow: Time of travel study of the reach East Hanney to Venn Mill. The distribution curve for the Rhodamine WT is shown with a 40 ppb standard solution allowing the actual Rhodamine WT concenti'ation in the river to be estimated. AVERAGE FLOW Time of Travel Study of the reach Venn Mill to Marcham
Time since tracer injected (minutes)
Figure 7 Average flow: Time of travel study of the reach Venn Mill to Marcham. The distribution curve for the Rhodamine WT is shown with a 40 ppb standard solution allowing the actual Rhodamine WT concentration in the river to be estimated. .VoItage_(m\/)- 0 x x 400 5 - i ' i -L -50 \ < 5 35 7 35 9 45 1 45 3 45 5 45 7 45 9 55 1 55 535 525 515 505 495 485 475 465 455 445 435 425 415 405 395 385 375 365 355 Time of TravelStudy of thereachMarcham R.confluence toThames to River Thames River Figure 8 Figure Average flow: Time of travel study o f the reach Marcham to confluence to confluence to Marcham f reach the o study travel of Time flow: Average , Abingdon iesnetae netd(iue) ' (minutes) injected tracer since Time , The distribution curve for the Rhodamine WT isshown WT Rhodamine the curve for distribution The AVERAGEFLOW 03/03/93
power cut . (Estimatedcut-off time i I ji ' r
Figure 0 Average flow: Time of travel study of the reach Marcham to confluence to River Thames, Abingdon. The distribution curve for the Rhodamine WT is shown with a 40 ppl) standard solution allowing the actual Rhodamine WT concentration in the river to be estimated. HIGH FLOW Time of Travel Study of the reach Above Wantage STW to East Hanney
Figure 10 High flow: Time of travel study of the reach Above Wantage STiV to East Hanney. The distribution curve for the Rhodamine WT is shown with a 40ppb standard solution allowing the actual Rhodamine WT concentration in the river to be estimated. Voltage (mV) solution allowing the actual Rhodamine WT concentration in the river to be to river the in concentration WT Rhodamine actual the allowing solution iue 11 Figure estimated. The distribution cui've fo r the Rhodamine WT is shown with a 40ppb standard 40ppb a with shown is WT Rhodamine the r fo cui've distribution The g lw: ieoftae td h ec atHne o Venn Mill to Hanney East reach f the o study travel f o Time : flow igh H Time of Travel Study of the reach East Hanney East toreach Mill Venn the of Study Travel of Time ie ic rcrijce (minutes) injected tracer since Time IH FLOW HIGH
. Voltage {mV) loigteata hdmn W ocnrto ntervrt e siae. There estimated. be to river the in concentration WT solution standard Rhodamine 40ppb a with actual the shown is WT allowing Rhodamine the r fo curve distribution is a question about the actual 'first arrival time arrival 'first actual the about question a is 12 Figure ihfo: ieoftae td h ec Vr ilt aca. The Marcham. to VermMill reach f the o study f travel o Time flow: High Time of Travel Study of the reach Venn MilltoMarcham Venn reach the of Study Travel of Time ie ic rcrijce (minutes) injected tracer since Time HIGH FLOW HIGH '
HIGH FLOW Time of Travel Study of the reach Marcham to confluence to R. Thames. 1000 J 15/04/93 900 -- 40 ppb standard
800 -- 700 600
500 Peak arrival time 400 Averaae travel time
300 First arrival time 200 100
_1qo220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 3/0 380 390
Time since tracer injected (minutes)
Figure 13 High flow: Time o f travel study of the reach Marcham to confluence to River Thames, Abingdon, The distribution curve for the Rhodamine WT is shown with a 40 ppb standard solution allowing the actual Rhodamine WT concentration hi the river to be estimated.