067008 Alyn at Pont-y-Capel 1998
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 9.054 2.370 1.190 1.364 2.519 1.088 0.968 0.724 0.730 4.988 6.786 2.463
2 7.936 2.334 1.209 3.688 2.287 3.307 0.927 0.714 0.607 3.408 7.381 2.307
3 11.020 2.217 9.987 5.139 2.077 1.677 0.891 0.930 0.592 2.705 6.944 2.288
4 17.770 2.061 13.840 3.887 1.989 1.179 0.875 0.719 0.592 2.274 6.639 2.253
5 14.050 1.931 8.437 3.256 2.058 1.109 0.873 0.631 0.592 1.938 5.766 2.353
6 10.450 1.952 15.870 2.873 1.929 1.316 0.879 0.597 0.533 1.626 4.954 2.069
7 12.880 1.939 9.719 2.545 1.777 1.267 0.820 0.588 0.556 1.411 4.473 2.035
8 13.740 1.819 7.366 5.990 1.631 1.285 0.799 0.577 0.577 1.184 4.865 2.300
9 9.769 1.715 5.710 6.671 1.512 1.299 0.818 0.572 2.087 1.177 4.416 2.029
10 7.678 1.594 5.096 6.711 1.560 1.771 0.793 0.572 1.284 1.266 3.525 2.237
11 6.405 1.489 5.770 9.848 1.521 3.487 0.852 0.552 1.440 1.161 3.204 2.162
12 6.111 1.392 4.923 8.454 1.412 1.764 0.862 0.536 10.410 0.985 3.455 3.680
13 8.974 1.318 4.518 7.465 1.307 2.572 0.846 0.543 9.290 0.941 3.948 3.702
14 10.210 1.299 3.859 7.744 1.257 2.975 0.840 0.574 5.164 1.036 5.116 3.308
15 7.143 1.273 3.479 11.250 1.212 2.108 0.764 0.554 3.600 0.909 3.843 3.392
16 6.544 1.208 3.174 14.300 1.154 1.841 0.742 0.522 2.684 2.021 3.331 2.964
17 5.943 1.159 2.909 14.760 1.107 1.939 0.821 0.518 2.104 2.695 3.059 2.759
18 11.240 1.155 2.617 11.390 1.082 2.884 0.746 0.512 1.703 2.377 2.826 3.535
19 9.361 1.131 2.401 10.100 1.063 1.985 0.793 0.510 1.438 2.131 2.587 6.131
20 6.744 1.137 2.244 8.601 1.038 1.636 0.949 0.512 1.221 3.175 2.365 4.883
21 6.507 1.194 2.095 7.735 1.025 1.381 0.878 0.568 1.069 2.869 2.183 3.838
22 5.594 1.178 1.973 7.237 1.002 1.172 0.762 0.546 0.962 6.998 2.409 3.498
23 4.798 1.106 1.868 6.377 1.016 1.143 0.777 1.647 0.893 9.353 2.438 3.285
24 4.225 1.073 2.060 5.243 1.014 1.201 0.726 1.212 0.861 12.400 2.709 3.049
25 3.769 1.056 2.579 4.614 1.000 1.046 0.689 0.875 0.850 10.640 2.267 3.080
26 3.476 1.055 2.041 4.604 1.085 1.038 0.774 0.912 0.869 7.174 3.507 3.258
27 3.224 1.177 1.755 4.136 1.009 1.653 0.767 0.728 0.846 9.455 2.792 3.104
28 2.994 1.303 1.590 3.528 1.000 1.286 0.709 0.653 0.808 8.182 2.869 3.644
29 2.800 1.604 3.100 0.959 1.059 0.649 0.625 0.815 7.476 3.377 3.125
30 2.644 1.503 2.774 0.922 1.023 0.791 0.602 7.357 8.882 2.748 2.919
31 2.492 1.355 0.929 0.705 0.613 6.852 2.689
Average 7.598 1.487 4.346 6.513 1.369 1.683 0.809 0.675 2.084 4.184 3.893 3.043
Lowest 2.492 1.055 1.190 1.364 0.922 1.023 0.649 0.510 0.533 0.909 2.183 2.029
Highest 17.770 2.370 15.870 14.760 2.519 3.487 0.968 1.647 10.410 12.400 7.381 6.131
Monthly total
(million cu m) 20.35 3.60 11.64 16.88 3.67 4.36 2.17 1.81 5.40 11.21 10.09 8.15
Runoff (mm) 90 16 51 74 16 19 10 8 24 49 44 36
Rainfall (mm) 129 26 104 133 22 128 54 61 125 142 76 72
Statistics of monthly data for previous record (Jun 1965 to Dec 1997)
Mean Avg. 4.185 3.730 3.076 2.405 1.656 1.190 0.832 0.823 0.947 1.759 2.933 4.240
flows: Low 1.016 1.233 0.766 0.840 0.676 0.438 0.331 0.286 0.391 0.452 0.614 1.245
(year) 1997 1992 1993 1997 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. 49 40 36 27 20 14 10 10 11 21 33 50
Low 12 14 9 10 8 5 4 3 4 5 7 15
High 94 97 95 74 67 33 25 29 45 81 70 112
Rainfall: Avg. 83 66 71 60 70 65 58 70 80 85 102 98
Low 7 5 16 4 18 14 15 7 9 16 48 25
High 154 158 131 138 164 153 134 172 276 172 198 186
Summary statistics Factors affecting runoff
1998
For 1998 For record As % of $ Reservoir(s) in catchment.
preceding 1998 pre-1998 $ Flow reduced by industrial and/or
Mean flow 3.150 2.309 136 agricultural abstractions.
Lowest yearly mean 1.266 1975 $ Augmentation from effluent returns.
Highest yearly mean 3.027 1969
Lowest monthly mean 0.675 Aug 0.286 Aug 1976
Highest monthly mean 7.598 Jan 9.481 Dec 1966
Lowest daily mean 0.510 19 Aug 0.241 24 Aug 1976
Highest daily mean 17.770 4 Jan 32.010 26 Sep 1976
10% exceedance 7.642 5.436 141
50% exceedance 2.037 1.269 161
95% exceedance 0.587 0.464 127
Annual total (million cu m) 99.34 72.86 136
Annual runoff (mm) 437 321 136
Annual rainfall (mm) 1072 908 118
{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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