067008 Alyn at Pont-y-Capel 2000
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 7.786 2.309 3.450 1.260 2.891 1.073 1.334 1.298 1.150 1.654 10.640 7.793
2 6.601 2.198 4.804 4.321 2.567 1.233 2.600 1.155 1.040 2.253 13.030 5.953
3 5.726 2.003 5.188 8.641 2.340 3.870 1.808 1.197 0.879 1.738 9.013 5.280
4 5.293 1.943 3.704 5.054 2.143 3.432 3.361 1.039 0.825 1.752 11.850 6.513
5 4.933 1.826 3.335 4.728 1.987 1.919 4.911 0.997 0.864 2.989 18.130 8.654
6 4.609 1.784 3.070 4.266 1.828 1.491 2.534 0.988 0.775 2.604 49.040 6.800
7 4.149 1.993 2.907 3.657 1.652 1.240 1.935 1.044 0.774 3.006 30.700 14.860
8 3.739 1.877 2.675 3.212 1.507 1.122 3.058 1.250 0.761 2.573 24.160 20.700
9 3.396 1.751 2.454 2.858 1.396 1.646 2.947 1.087 0.735 4.056 24.980 19.140
10 3.236 2.557 2.354 2.601 1.314 1.229 16.110 1.022 0.723 4.798 24.320 17.580
11 2.983 2.268 2.147 2.840 1.233 1.034 10.880 0.967 0.708 3.194 19.410 16.270
12 11.510 3.205 2.007 3.509 1.187 0.978 6.216 0.987 0.689 3.293 16.410 15.710
13 10.400 2.496 1.867 4.854 1.168 0.939 4.838 1.593 0.687 3.412 10.950 15.670
14 7.120 2.757 1.815 4.051 1.123 1.406 3.758 2.290 0.706 3.700 9.599 14.330
15 5.631 3.322 1.684 3.318 1.089 1.153 3.017 1.546 1.224 3.228 8.266 11.250
16 4.906 3.383 1.599 3.457 1.127 1.021 2.565 1.296 1.170 3.017 7.435 9.074
17 4.353 3.385 1.647 7.546 1.364 0.945 2.181 1.112 1.192 2.851 7.230 7.646
18 3.931 3.885 1.565 5.157 1.336 0.882 1.891 1.060 1.995 2.623 6.769 6.566
19 3.576 3.423 1.476 4.393 1.154 0.832 1.643 0.988 1.787 2.267 7.956 6.263
20 3.306 2.930 1.418 3.767 1.238 0.841 1.459 0.979 2.399 2.061 12.910 5.557
21 3.092 2.709 1.387 3.348 1.139 0.904 1.305 1.644 1.526 1.837 12.570 4.931
22 3.049 2.489 1.345 3.480 1.037 1.070 1.170 1.375 1.254 1.700 12.010 4.586
23 2.745 2.352 1.960 2.987 1.045 0.884 1.089 0.998 1.029 1.675 8.426 4.334
24 2.597 2.203 1.732 4.698 1.023 0.908 1.036 0.894 1.546 1.672 7.123 5.522
25 2.427 2.048 1.476 6.850 1.079 0.842 1.046 1.020 3.265 1.730 9.970 4.670
26 2.440 1.935 1.713 5.989 1.550 0.804 1.037 1.098 3.707 1.553 10.700 4.158
27 2.374 3.045 1.508 5.190 1.435 0.778 1.203 0.875 3.023 1.791 8.075 3.838
28 2.356 3.536 1.378 4.388 1.167 0.769 1.843 1.032 2.872 5.090 8.705 3.646
29 2.480 3.777 1.308 4.083 1.029 0.771 1.458 0.939 2.216 11.870 7.172 3.396
30 2.666 1.265 3.345 0.999 0.788 1.213 0.837 1.825 24.710 6.448 3.202
31 2.296 1.243 1.023 1.811 1.026 17.730 4.007
Average 4.378 2.600 2.177 4.262 1.425 1.227 3.008 1.149 1.445 4.143 13.800 8.642
Lowest 2.296 1.751 1.243 1.260 0.999 0.769 1.036 0.837 0.687 1.553 6.448 3.202
Highest 11.510 3.885 5.188 8.641 2.891 3.870 16.110 2.290 3.707 24.710 49.040 20.700
Monthly total
(million cu m) 11.73 6.51 5.83 11.05 3.82 3.18 8.06 3.08 3.75 11.10 35.77 23.15
Runoff (mm) 52 29 26 49 17 14 35 14 16 49 158 102
Rainfall (mm) 58 78 35 133 48 70 146 78 91 167 242 149
Statistics of monthly data for previous record (Jun 1965 to Dec 1999)
Mean Avg. 4.341 3.660 3.137 2.508 1.628 1.195 0.824 0.824 1.054 1.974 3.008 4.288
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 2.098 2.456 3.906 6.896 6.168 9.481
(year) 1995 1977 1979 1998 1969 1977 1973 1986 1976 1976 1984 1966
Runoff: Avg. 51 39 37 29 19 14 10 10 12 23 34 51
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. 86 65 72 63 68 67 57 72 84 89 101 99
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
2000
For 2000 For record As % of $ Reservoir(s) in catchment.
preceding 2000 pre-2000 $ Flow reduced by industrial and/or
Mean flow 4.016 2.365 170 agricultural abstractions.
Lowest yearly mean 1.266 1975 $ Augmentation from effluent returns.
Highest yearly mean 3.413 1999
Lowest monthly mean 1.149 Aug 0.286 Aug 1976
Highest monthly mean 13.800 Nov 9.481 Dec 1966
Lowest daily mean 0.687 13 Sep 0.241 24 Aug 1976
Highest daily mean 49.040 6 Nov 32.010 26 Sep 1976
10% exceedance 8.907 5.602 159
50% exceedance 2.365 1.311 180
95% exceedance 0.852 0.468 182
Annual total (million cu m) 127.00 74.63 170
Annual runoff (mm) 559 329 170
Annual rainfall (mm) 1295 923 140
{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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