067008 Alyn at Pont-y-Capel 2001
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 6.951 3.103 2.545 3.428 2.463 1.405 0.876 0.683 0.976 1.899 2.729 2.154
2 8.710 3.391 2.428 3.578 2.279 1.527 0.845 0.809 0.828 1.260 2.387 1.959
3 6.321 4.270 2.306 6.434 2.251 1.388 3.547 0.950 0.915 1.053 2.215 2.875
4 5.806 9.655 2.183 9.729 2.045 1.325 2.220 0.857 0.919 1.010 2.102 4.134
5 4.971 8.003 2.060 9.979 1.887 1.301 1.241 0.929 1.298 1.185 1.986 3.236
6 4.429 7.928 2.700 9.260 1.781 1.295 1.162 1.437 1.343 1.405 1.974 3.014
7 4.244 11.140 3.695 9.514 1.708 1.293 1.145 2.406 1.035 4.926 3.297 2.860
8 4.675 7.411 2.745 9.211 1.617 1.377 1.034 1.405 1.294 4.862 4.236 2.529
9 4.080 5.756 2.432 7.693 1.598 1.261 0.965 0.974 0.916 8.031 2.879 2.328
10 3.765 5.222 2.283 7.003 1.680 1.221 0.985 0.857 0.816 4.666 2.539 2.180
11 3.472 6.377 2.181 5.622 1.517 1.200 1.025 0.831 0.766 3.597 2.441 2.046
12 3.241 11.160 2.142 4.913 1.450 1.116 0.907 0.912 1.050 2.834 4.018 1.942
13 3.014 6.547 2.016 4.304 3.051 1.095 0.902 0.843 1.813 2.390 3.529 1.835
14 2.851 5.450 1.935 5.964 8.084 1.167 0.853 0.788 1.464 2.188 3.027 1.703
15 2.764 4.769 1.864 5.362 6.661 1.449 0.826 1.050 1.419 1.953 2.664 1.628
16 2.616 4.250 2.024 4.075 3.801 1.211 0.809 1.103 1.577 1.724 2.456 1.579
17 2.472 3.856 2.330 4.094 6.729 1.134 1.050 0.840 1.526 1.669 2.301 1.495
18 2.381 3.537 2.353 3.781 3.950 1.047 2.476 1.045 1.235 1.980 2.166 1.471
19 2.280 3.286 2.151 3.324 3.181 1.046 1.427 1.963 2.265 3.934 1.997 1.542
20 2.197 3.081 2.083 3.028 2.767 1.023 1.029 1.509 2.021 16.210 1.871 1.701
21 2.267 3.022 2.724 2.850 2.458 0.989 0.935 1.046 1.439 7.896 1.840 1.717
22 3.906 3.159 8.796 7.600 2.196 0.976 0.882 0.866 1.180 5.536 1.758 1.561
23 6.971 3.286 7.812 5.248 1.958 0.961 0.830 0.796 1.081 4.754 1.625 1.500
24 4.758 2.944 5.761 5.313 1.772 0.949 0.811 0.816 1.666 3.779 1.520 1.891
25 3.604 2.757 4.550 4.719 1.653 0.928 0.790 0.772 1.781 3.996 1.917 2.175
26 4.072 2.861 3.901 3.870 1.620 0.928 0.769 0.734 1.351 5.298 1.758 1.971
27 3.347 2.900 8.917 3.480 1.612 0.897 0.746 0.700 1.369 3.790 2.078 2.083
28 3.088 2.770 7.515 3.335 1.458 0.923 0.728 0.689 1.240 3.067 2.105 1.931
29 3.054 5.483 3.039 1.342 0.931 0.704 0.671 1.074 2.711 2.612 1.959
30 3.292 4.338 2.741 1.456 0.887 0.697 0.892 1.895 2.935 2.193 2.043
31 3.076 3.908 1.428 0.695 1.845 3.631 1.709
Average 3.957 5.068 3.554 5.416 2.563 1.142 1.094 1.033 1.318 3.747 2.407 2.089
Lowest 2.197 2.757 1.864 2.741 1.342 0.887 0.695 0.671 0.766 1.010 1.520 1.471
Highest 8.710 11.160 8.917 9.979 8.084 1.527 3.547 2.406 2.265 16.210 4.236 4.134
Monthly total
(million cu m) 10.60 12.26 9.52 14.04 6.87 2.96 2.93 2.77 3.42 10.04 6.24 5.59
Runoff (mm) 47 54 42 62 30 13 13 12 15 44 27 25
Rainfall (mm) 59 86 71 125 70 32 81 116 98 133 55 59
Statistics of monthly data for previous record (Jun 1965 to Dec 2000)
Mean Avg. 4.342 3.629 3.110 2.558 1.622 1.196 0.885 0.833 1.065 2.034 3.307 4.409
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 6.513 5.657 2.873 3.008 2.456 3.906 6.896 13.800 9.481
(year) 1995 1977 1979 1998 1969 1977 2000 1986 1976 1976 2000 1966
Runoff: Avg. 51 39 37 29 19 14 10 10 12 24 38 52
Low 12 14 9 10 8 5 4 3 4 5 7 15
High 94 97 95 74 67 33 35 29 45 81 158 112
Rainfall: Avg. 85 66 71 65 67 67 59 72 84 91 105 100
Low 7 5 16 4 18 14 15 7 9 16 48 25
High 154 158 131 138 164 153 146 172 276 172 242 186
Summary statistics Factors affecting runoff
2001
For 2001 For record As % of $ Reservoir(s) in catchment.
preceding 2001 pre-2001 $ Flow reduced by industrial and/or
Mean flow 2.766 2.411 115 agricultural abstractions.
Lowest yearly mean 1.266 1975 $ Augmentation from effluent returns.
Highest yearly mean 4.016 2000
Lowest monthly mean 1.033 Aug 0.286 Aug 1976
Highest monthly mean 5.416 Apr 13.800 Nov 2000
Lowest daily mean 0.671 29 Aug 0.241 24 Aug 1976
Highest daily mean 16.210 20 Oct 49.040 6 Nov 2000
10% exceedance 5.550 5.669 98
50% exceedance 2.092 1.340 156
95% exceedance 0.807 0.469 172
Annual total (million cu m) 87.23 76.09 115
Annual runoff (mm) 384 335 115
Annual rainfall (mm) 985 932 106
{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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