067008 Alyn at Pont-y-Capel 1999
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 3.725 4.844 5.614 1.529 1.197 0.762 0.781 0.657 0.600 15.040 3.820 2.512
2 6.623 4.298 7.473 2.343 1.128 2.917 0.716 1.576 0.588 16.400 3.729 2.431
3 6.397 3.819 8.650 1.641 1.102 1.800 0.701 1.070 0.585 20.040 3.109 3.952
4 5.337 3.493 7.294 1.632 1.109 1.302 0.731 0.843 0.575 17.970 2.846 3.282
5 6.270 3.355 6.270 1.595 1.113 1.158 0.700 0.905 0.568 10.460 11.230 3.581
6 5.626 3.372 5.605 1.655 1.106 1.096 0.660 1.012 0.597 7.523 10.740 3.244
7 5.856 3.132 7.153 1.518 1.246 1.031 0.626 1.545 0.808 6.213 7.179 3.026
8 5.224 3.117 6.055 1.367 1.286 0.876 0.598 0.900 0.635 5.303 5.659 4.200
9 4.430 2.776 6.113 1.291 1.168 0.810 0.578 2.314 0.605 4.411 4.696 4.338
10 3.829 2.546 5.651 1.218 1.265 0.780 0.563 1.818 0.551 3.742 3.974 5.098
11 3.437 2.507 4.848 1.355 1.101 0.760 0.554 0.988 0.575 3.202 3.512 8.489
12 3.799 2.479 4.292 1.641 1.058 0.818 0.555 0.819 0.554 2.792 3.182 12.470
13 4.033 2.625 3.733 1.698 1.042 0.739 0.595 0.899 0.534 2.490 2.875 10.700
14 3.808 2.975 3.335 1.537 1.040 0.712 0.579 0.835 0.531 2.262 2.611 8.674
15 8.104 2.907 3.030 1.940 0.984 0.682 0.556 0.705 0.524 2.037 2.674 6.940
16 9.374 2.690 2.786 1.622 0.950 0.652 0.529 0.953 0.545 1.841 5.444 7.356
17 7.926 3.689 2.575 1.494 0.925 0.639 0.519 0.956 0.528 1.666 6.192 8.914
18 7.897 3.473 2.383 1.456 0.913 0.630 0.510 1.592 3.937 1.531 7.314 6.697
19 6.907 2.829 2.228 1.412 0.898 0.633 0.553 1.719 12.620 1.458 5.110 5.521
20 6.693 2.456 2.146 3.522 0.868 0.725 0.568 0.976 16.020 1.387 4.312 4.906
21 5.344 4.671 3.122 3.323 0.867 0.700 0.511 0.790 6.878 1.497 3.767 5.676
22 4.686 5.563 2.855 2.749 0.836 0.654 0.534 0.711 4.660 2.212 3.495 6.750
23 4.314 4.952 2.367 2.134 0.818 0.705 0.519 0.686 6.372 2.121 3.115 6.271
24 4.160 5.576 2.128 1.891 0.863 0.643 0.511 0.739 3.798 14.420 4.733 12.910
25 4.443 4.387 2.316 1.810 0.773 0.599 0.506 1.108 5.098 21.850 5.550 9.842
26 7.345 3.971 2.134 2.413 0.754 0.649 0.492 0.826 5.334 13.340 4.265 10.240
27 8.624 3.534 1.883 1.902 0.797 1.101 0.488 0.702 5.427 8.072 3.671 9.071
28 13.210 3.760 1.753 1.627 0.810 0.711 0.480 0.659 4.007 6.242 3.420 11.450
29 8.164 1.968 1.397 0.747 0.646 0.472 0.639 11.560 5.137 3.016 9.757
30 6.652 1.700 1.299 0.796 0.715 0.471 0.626 11.050 5.165 2.789 12.430
31 5.582 1.557 0.746 0.463 0.622 4.243 9.759
Average 6.059 3.564 3.904 1.800 0.978 0.888 0.568 1.006 3.555 6.841 4.601 7.112
Lowest 3.437 2.456 1.557 1.218 0.746 0.599 0.463 0.622 0.524 1.387 2.611 2.431
Highest 13.210 5.576 8.650 3.522 1.286 2.917 0.781 2.314 16.020 21.850 11.230 12.910
Monthly total
(million cu m) 16.23 8.62 10.46 4.67 2.62 2.30 1.52 2.69 9.22 18.32 11.93 19.05
Runoff (mm) 71 38 46 21 12 10 7 12 41 81 53 84
Rainfall (mm) 131 69 70 68 34 76 19 127 184 152 96 160
Statistics of monthly data for previous record (Jun 1965 to Dec 1998)
Mean Avg. 4.289 3.662 3.114 2.530 1.647 1.205 0.831 0.819 0.980 1.831 2.961 4.205
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 11 22 34 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. 84 65 72 62 69 67 58 70 81 87 102 97
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
1999
For 1999 For record As % of $ Reservoir(s) in catchment.
preceding 1999 pre-1999 $ Flow reduced by industrial and/or
Mean flow 3.413 2.334 146 agricultural abstractions.
Lowest yearly mean 1.266 1975 $ Augmentation from effluent returns.
Highest yearly mean 3.150 1998
Lowest monthly mean 0.568 Jul 0.286 Aug 1976
Highest monthly mean 7.112 Dec 9.481 Dec 1966
Lowest daily mean 0.463 31 Jul 0.241 24 Aug 1976
Highest daily mean 21.850 25 Oct 32.010 26 Sep 1976
10% exceedance 7.727 5.522 140
50% exceedance 2.316 1.290 180
95% exceedance 0.542 0.466 116
Annual total (million cu m) 107.60 73.65 146
Annual runoff (mm) 474 324 146
Annual rainfall (mm) 1186 914 130
{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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