067008 Alyn at Pont-y-Capel 1996
Measuring authority: EA Grid reference: 33 (SJ) 336 541 Catchment area (sq km): 227.1
First year: 1965 Level stn. (m OD): 37.30 Max alt. (m OD): 562
Daily mean gauged discharges (cubic metres per second)
DAY JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
1 1.787 1.017 2.051 1.860 2.999 0.827 0.686 0.460 0.461 0.398 1.012 7.389
2 2.406 1.000 1.929 1.748 2.929 1.072 0.635 0.492 0.459 0.395 1.012 5.624
3 2.730 0.975 1.832 1.600 2.165 1.009 0.666 0.468 0.463 0.501 0.760 7.103
4 2.753 0.951 1.733 1.486 1.829 0.854 0.683 0.444 0.443 0.550 0.878 6.800
5 3.287 0.974 1.621 1.413 1.633 0.792 0.650 0.435 0.457 0.511 0.956 5.230
6 5.369 1.051 1.523 1.334 1.487 0.764 0.592 0.768 0.436 0.434 0.912 4.183
7 7.564 1.013 1.450 1.260 1.347 0.795 0.580 0.732 0.436 0.426 1.200 3.542
8 7.414 1.039 1.457 1.195 1.216 0.767 0.560 0.542 0.434 0.412 0.991 3.143
9 5.805 3.662 1.446 1.152 1.121 0.726 0.573 0.492 0.432 0.412 0.820 2.811
10 4.399 11.500 1.299 1.139 1.084 0.712 0.552 0.592 0.435 0.414 0.744 2.506
11 4.517 10.400 2.695 1.143 1.067 0.795 0.548 0.536 0.440 0.407 0.679 2.272
12 5.028 10.860 4.118 2.625 1.038 0.707 0.561 0.477 0.428 0.404 0.675 2.098
13 4.743 6.722 2.625 2.572 0.992 0.677 0.543 0.448 0.416 0.402 0.626 1.929
14 3.536 4.961 2.269 2.451 0.969 0.666 0.534 0.439 0.417 0.827 0.614 1.771
15 3.014 4.184 2.539 2.009 0.957 0.645 0.523 0.431 0.410 0.736 0.620 1.634
16 2.671 3.756 2.701 2.168 0.941 0.624 0.507 0.435 0.407 0.953 0.685 1.514
17 2.426 4.032 2.294 2.148 0.930 0.608 0.501 0.430 0.393 0.716 1.530 1.435
18 2.220 6.215 2.024 2.014 1.056 0.623 0.488 0.408 0.386 0.870 1.082 1.694
19 2.063 4.291 1.824 1.719 1.679 0.615 0.486 0.411 0.399 0.652 1.586 5.393
20 1.883 3.297 1.974 1.515 1.187 0.587 0.474 0.468 0.391 0.713 3.139 7.371
21 1.735 3.038 4.639 1.711 1.026 0.582 0.469 0.437 0.399 0.574 2.853 4.686
22 1.636 3.138 3.969 2.284 1.054 0.573 0.471 0.467 0.401 0.513 3.552 3.428
23 1.585 3.007 3.658 5.229 1.516 0.565 0.460 0.865 0.399 0.482 3.617 2.982
24 1.532 3.414 3.834 2.926 1.549 0.566 0.461 0.550 0.422 0.462 5.665 2.595
25 1.353 3.469 3.147 2.313 1.098 0.568 0.453 0.579 0.431 0.621 13.350 2.276
26 1.216 2.895 3.376 2.007 1.099 0.637 0.484 0.723 0.410 0.734 11.660 2.042
27 1.198 2.545 2.954 1.798 1.128 0.764 0.464 0.964 0.403 0.593 7.573 2.156
28 1.146 2.320 2.595 1.641 1.060 1.083 0.590 0.719 0.399 0.724 6.003 1.922
29 1.105 2.172 2.329 1.578 0.995 0.704 0.554 0.578 0.505 0.674 11.160 1.748
30 1.082 2.117 1.650 0.944 0.660 0.489 0.497 0.422 0.552 9.747 1.706
31 1.050 1.990 0.843 0.465 0.470 1.096 1.560
Average 2.911 3.721 2.452 1.923 1.321 0.719 0.539 0.540 0.424 0.586 3.190 3.308
Lowest 1.050 0.951 1.299 1.139 0.843 0.565 0.453 0.408 0.386 0.395 0.614 1.435
Highest 7.564 11.500 4.639 5.229 2.999 1.083 0.686 0.964 0.505 1.096 13.350 7.389
Monthly total
(million cu m) 7.80 9.32 6.57 4.98 3.54 1.86 1.44 1.45 1.10 1.57 8.27 8.86
Runoff (mm) 34 41 29 22 16 8 6 6 5 7 36 39
Rainfall (mm) 47 72 58 69 59 37 27 84 18 100 134 59
Statistics of monthly data for previous record (Jun 1965 to Dec 1995)
Mean Avg. 4.334 3.769 3.143 2.473 1.657 1.156 0.828 0.836 0.976 1.832 2.951 4.269
flows: Low 1.327 1.233 0.766 1.024 0.676 0.438 0.331 0.286 0.391 0.452 0.614 1.245
(year) 1989 1992 1993 1973 1990 1976 1976 1976 1991 1969 1975 1975
High 7.967 9.085 8.027 6.474 5.657 2.873 2.098 2.456 3.906 6.896 6.168 9.481
(year) 1995 1977 1979 1986 1969 1977 1973 1986 1976 1976 1984 1966
Runoff: Avg. 51 40 37 28 20 13 10 10 11 22 34 50
Low 16 14 9 12 8 5 4 3 4 5 7 15
High 94 97 95 74 67 33 25 29 45 81 70 112
Rainfall: Avg. 87 65 73 61 70 63 60 69 84 85 101 99
Low 22 5 16 4 18 14 15 7 9 16 48 25
High 154 158 131 138 164 132 134 172 276 172 198 186
Summary statistics Factors affecting runoff
1996
For 1996 For record As % of $ Reservoir(s) in catchment.
preceding 1996 pre-1996 $ Flow reduced by industrial and/or
Mean flow 1.795 2.346 77 agricultural abstractions.
Lowest yearly mean 1.266 1975 $ Augmentation from effluent returns.
Highest yearly mean 3.027 1969
Lowest monthly mean 0.424 Sep 0.286 Aug 1976
Highest monthly mean 3.721 Feb 9.481 Dec 1966
Lowest daily mean 0.386 18 Sep 0.241 24 Aug 1976
Highest daily mean 13.350 25 Nov 32.010 26 Sep 1976
10% exceedance 3.963 5.543 71
50% exceedance 1.045 1.307 80
95% exceedance 0.411 0.466 88
Annual total (million cu m) 56.76 74.03 77
Annual runoff (mm) 250 326 77
Annual rainfall (mm) 764 917 83
{1961-90 rainfall average (mm) 916}
Station and catchment description
The divide wall of this (two part) asymmetrical compound Crump weir was lowered in 1986 as debris regularly blocked the
lower part. Current meter calibration took place before and after.
Ill-defined catchment boundary to NE and SE. 25% Carboniferous Limestone. Major loss of water from upper 70 sq.km. in
limestone and mine drainage tunnels. Extensive glacial deposits over Coal Measures.
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