067008 Alyn at Pont-y-Capel 1997
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 1.470 0.748 3.528 0.893 0.717 0.648 4.067 0.728 0.861 0.503 0.531 5.097
2 1.410 0.755 3.358 0.878 0.683 0.629 3.276 0.665 0.672 0.474 0.585 4.014
3 1.332 0.743 2.798 0.856 0.682 0.621 2.745 0.651 0.729 0.463 0.551 3.257
4 1.249 0.784 2.921 0.839 0.730 0.619 2.304 0.625 0.657 0.463 0.580 2.824
5 1.175 0.737 2.748 0.843 1.232 0.607 1.962 0.603 0.590 0.459 0.741 2.557
6 1.126 0.755 2.552 0.836 1.527 0.635 1.727 0.583 0.580 0.572 0.687 2.319
7 1.092 0.946 2.268 0.879 2.612 0.647 1.531 0.570 0.621 0.628 1.189 2.187
8 1.064 0.802 2.031 0.824 6.645 0.591 1.346 0.555 0.602 0.760 2.843 2.282
9 1.029 0.793 1.980 0.793 4.701 0.581 1.180 0.545 0.551 1.061 1.618 2.064
10 0.987 1.016 1.859 0.778 4.732 0.786 1.083 0.814 0.536 0.654 1.570 2.581
11 1.098 1.132 1.695 0.769 5.653 2.168 0.987 0.736 0.535 1.106 1.245 3.706
12 1.432 1.740 1.571 0.753 3.861 2.903 0.959 0.590 0.566 1.103 0.999 3.020
13 1.262 3.334 1.493 0.750 3.046 1.199 0.970 0.826 0.562 0.926 0.913 2.502
14 1.104 1.974 1.504 0.716 2.494 1.118 0.980 0.629 0.523 0.902 0.837 2.252
15 1.029 1.538 1.367 0.701 2.101 0.935 0.938 0.572 0.503 1.402 0.797 2.046
16 1.001 1.834 1.237 0.686 2.008 0.806 1.017 0.543 0.503 1.053 1.069 1.910
17 0.986 2.880 1.135 0.679 2.052 0.725 1.304 0.569 0.507 0.814 1.060 1.930
18 0.941 3.603 1.308 0.682 1.663 0.704 0.911 0.532 0.507 0.707 2.368 6.182
19 0.935 4.031 1.230 0.688 1.558 0.879 0.826 0.533 0.562 0.660 1.867 3.702
20 0.863 3.994 1.100 0.677 1.620 1.101 0.790 0.899 0.516 0.607 1.870 2.901
21 0.844 4.363 1.059 0.675 1.626 1.947 0.753 0.926 0.495 0.580 1.600 2.522
22 0.902 3.390 1.076 0.663 1.279 1.910 0.730 0.708 0.489 0.574 1.299 2.595
23 0.860 3.619 1.160 0.648 1.095 1.151 0.714 0.754 0.483 0.557 1.305 3.285
24 0.841 5.865 1.421 0.694 0.967 1.068 0.784 0.660 0.480 0.548 1.667 3.958
25 0.829 5.304 1.195 1.938 0.869 7.107 0.774 0.585 0.485 0.537 1.580 5.100
26 0.810 6.922 1.086 1.339 0.823 16.200 0.804 0.549 0.479 0.538 1.441 8.185
27 0.786 4.969 1.076 1.028 0.799 12.760 0.740 0.632 0.483 0.534 1.369 7.688
28 0.765 4.025 1.033 1.031 0.758 9.473 0.673 0.780 0.476 0.514 12.200 12.650
29 0.756 0.964 0.890 0.726 6.449 0.666 0.886 0.488 0.510 9.716 11.280
30 0.760 0.931 0.773 0.698 4.776 0.637 0.930 0.532 0.558 6.810 8.735
31 0.745 0.914 0.676 0.714 1.240 0.527 7.097
Average 1.016 2.593 1.664 0.840 1.956 2.725 1.255 0.691 0.552 0.687 2.097 4.272
Lowest 0.745 0.737 0.914 0.648 0.676 0.581 0.637 0.532 0.476 0.459 0.531 1.910
Highest 1.470 6.922 3.528 1.938 6.645 16.200 4.067 1.240 0.861 1.402 12.200 12.650
Monthly total
(million cu m) 2.72 6.27 4.46 2.18 5.24 7.06 3.36 1.85 1.43 1.84 5.43 11.44
Runoff (mm) 12 28 20 10 23 31 15 8 6 8 24 50
Rainfall (mm) 7 101 35 41 92 153 42 85 23 65 112 106
Statistics of monthly data for previous record (Jun 1965 to Dec 1996)
Mean Avg. 4.288 3.767 3.121 2.456 1.646 1.142 0.819 0.827 0.959 1.793 2.959 4.239
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 19 13 10 10 11 21 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. 85 65 72 61 69 62 59 70 82 86 102 98
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
1997
For 1997 For record As % of $ Reservoir(s) in catchment.
preceding 1997 pre-1997 $ Flow reduced by industrial and/or
Mean flow 1.690 2.329 73 agricultural abstractions.
Lowest yearly mean 1.266 1975 $ Augmentation from effluent returns.
Highest yearly mean 3.027 1969
Lowest monthly mean 0.552 Sep 0.286 Aug 1976
Highest monthly mean 4.272 Dec 9.481 Dec 1966
Lowest daily mean 0.459 5 Oct 0.241 24 Aug 1976
Highest daily mean 16.200 26 Jun 32.010 26 Sep 1976
10% exceedance 3.654 5.484 67
50% exceedance 0.936 1.296 72
95% exceedance 0.509 0.463 110
Annual total (million cu m) 53.30 73.50 73
Annual runoff (mm) 235 324 73
Annual rainfall (mm) 862 911 95
{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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