018005 Allan Water at Bridge of Allan 1998
Measuring authority: SEPA Grid reference: 26 (NS) 786 980 Catchment area (sq km): 210.0
First year: 1971 Level stn. (m OD): 11.20 Max alt. (m OD): 633
Daily mean gauged discharges (cubic metres per second)
DAY JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
1 16.610 3.924 7.512 5.605 3.207 2.332 2.292 2.742 20.350 13.750 6.493 7.422
2 14.950 3.649 9.528 5.913 2.985 1.990 2.030 2.553 13.530 6.665 7.206 6.451
3 44.220 4.258 13.480 21.340 2.796 1.819 1.885 18.160 5.944 4.073 8.507 5.780
4 24.650 5.584 10.320 56.220 2.671 1.705 1.790 5.482 4.512 3.428 6.329 5.168
5 15.570 6.059 7.733 30.450 2.887 1.651 1.739 4.022 3.584 3.163 10.000 4.699
6 11.970 8.918 7.091 15.690 2.924 2.418 1.673 6.399 3.137 2.867 7.318 4.261
7 14.150 9.049 12.900 19.000 10.190 4.862 1.585 12.630 2.976 2.592 6.964 10.620
8 12.380 12.380 9.744 28.330 4.740 3.248 1.569 11.320 11.300 2.363 8.916 18.790
9 26.500 16.780 7.682 12.470 3.489 10.200 1.586 5.506 15.140 8.640 27.830 7.461
10 13.930 13.720 18.710 8.598 3.014 8.653 1.597 4.516 8.004 4.570 12.170 12.220
11 12.120 68.870 11.110 6.942 2.778 4.901 1.584 4.852 5.607 4.120 8.631 15.290
12 10.120 20.330 8.228 5.948 2.700 3.375 4.376 4.541 4.616 4.752 13.150 12.130
13 12.360 20.050 7.086 5.271 2.564 2.767 4.549 3.860 3.852 6.384 16.680 19.710
14 15.450 24.670 5.884 4.779 2.463 2.428 2.388 5.829 3.317 6.335 8.289 17.840
15 17.030 17.930 5.225 4.434 2.405 2.694 1.921 4.502 2.963 6.287 6.496 17.790
16 11.010 12.620 4.963 4.220 2.292 3.559 2.053 6.750 2.707 44.370 5.625 13.380
17 23.260 8.969 4.698 3.780 2.156 3.187 5.276 8.584 2.559 20.920 5.077 18.450
18 23.750 7.598 4.141 3.515 2.050 2.496 3.888 4.075 2.712 14.660 4.814 11.760
19 13.340 6.996 3.843 3.368 2.053 2.555 20.930 3.421 2.473 9.929 4.467 7.955
20 9.119 18.110 3.637 3.406 2.132 2.284 12.110 5.082 2.306 53.850 8.584 6.392
21 9.142 9.941 3.424 3.468 2.049 1.944 8.855 4.024 2.189 72.720 20.110 5.837
22 12.300 9.962 3.257 4.826 1.945 1.982 9.543 3.015 2.124 58.080 27.330 8.598
23 12.030 16.760 3.148 5.898 1.922 3.079 9.857 3.853 2.067 38.700 12.360 8.803
24 8.133 9.418 3.217 4.381 1.875 5.551 5.112 4.005 2.011 52.030 14.420 24.310
25 6.844 7.067 3.261 4.665 1.857 2.980 3.934 2.925 1.965 17.280 10.120 26.980
26 5.900 8.348 16.320 6.422 1.876 5.016 4.830 2.594 1.956 15.090 23.140 49.500
27 5.259 19.240 6.765 5.967 1.941 6.404 5.022 2.389 2.628 32.430 22.250 31.320
28 4.874 9.053 5.004 4.602 1.968 4.364 3.711 2.273 3.071 24.140 35.150 12.050
29 4.547 15.050 3.954 2.020 3.209 4.562 2.177 2.478 12.190 11.230 10.780
30 4.329 16.890 3.497 2.055 2.769 4.056 2.066 3.515 9.223 8.800 11.720
31 4.137 7.302 2.564 3.280 2.031 7.608 8.532
Average 13.550 13.580 7.973 9.899 2.728 3.547 4.503 5.038 4.853 18.170 12.280 13.610
Lowest 4.137 3.649 3.148 3.368 1.857 1.651 1.569 2.031 1.956 2.363 4.467 4.261
Highest 44.220 68.870 18.710 56.220 10.190 10.200 20.930 18.160 20.350 72.720 35.150 49.500
Monthly total
(million cu m) 36.29 32.85 21.35 25.66 7.31 9.19 12.06 13.49 12.58 48.66 31.83 36.46
Runoff (mm) 173 156 102 122 35 44 57 64 60 232 152 174
Rainfall (mm) 150 168 110 118 54 113 131 108 93 249 170 181
Statistics of monthly data for previous record (Jul 1971 to Dec 1997)
Mean Avg. 12.070 9.895 9.908 5.183 3.725 2.660 2.201 2.887 4.795 7.505 8.920 10.230
flows: Low 4.073 3.631 3.152 1.655 1.189 0.945 0.726 0.649 0.906 0.972 3.641 3.709
(year) 1997 1986 1975 1974 1980 1974 1984 1984 1972 1972 1972 1975
High 28.570 22.490 24.460 10.410 15.430 5.424 6.309 12.390 15.180 15.060 17.760 22.420
(year) 1993 1995 1994 1993 1986 1972 1985 1985 1992 1995 1984 1994
Runoff: Avg. 154 115 126 64 48 33 28 37 59 96 110 130
Low 52 42 40 20 15 12 9 8 11 12 45 47
High 364 259 312 129 197 67 80 158 187 192 219 286
Rainfall: Avg. 159 112 132 68 76 74 80 90 121 138 136 144
Low 52 21 42 4 13 17 17 13 6 29 42 40
High 379 317 299 123 201 151 218 223 249 255 258 270
Summary statistics Factors affecting runoff
1998
For 1998 For record As % of $ Flow reduced by industrial and/or
preceding 1998 pre-1998 agricultural abstractions.
Mean flow 9.124 6.655 137
Lowest yearly mean 4.270 1975
Highest yearly mean 9.090 1986
Lowest monthly mean 2.728 May 0.649 Aug 1984
Highest monthly mean 18.170 Oct 28.570 Jan 1993
Lowest daily mean 1.569 8 Jul 0.578 27 Aug 1984
Highest daily mean 72.720 21 Oct 139.300 16 Jan 1993
10% exceedance 18.990 15.340 124
50% exceedance 5.691 3.948 144
95% exceedance 1.936 0.889 218
Annual total (million cu m) 287.70 210.00 137
Annual runoff (mm) 1370 1000 137
Annual rainfall (mm) 1645 1330 124
{1961-90 rainfall average (mm) 1335}
Station and catchment description
Velocity-area station; recorder sited in natural reach with vertical stone wall on rb. Lb steep to 2.6m. Flood rating
stable but large boulders make c/m a problem at low flows. As site is within a caravan park the low flow control is
susceptible to rearrangment by children. Station useful for obtaining flood data, as flooding frequently occurs in the
town of Bridge of Allan.
The Allan Water occupies a broad flat valley with steep lateral tributaries. Geology: predominantly Old Red Sandstone.
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