041019 Arun at Alfoldean 1997
Measuring authority: EA Grid reference: 51 (TQ) 117 331 Catchment area (sq km): 139.0
First year: 1970 Level stn. (m OD): 21.40 Max alt. (m OD): 294
Daily mean gauged discharges (cubic metres per second)
DAY JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
1 0.432 0.558 2.123 0.350 0.272 0.196 0.538 0.234 0.268 0.147 0.185 1.800
2 0.408 0.557 1.912 0.343 0.268 0.193 0.436 0.185 0.215 0.167 0.191 5.261
3 0.410 0.524 1.935 0.335 0.263 0.208 0.481 0.212 0.180 0.149 0.220 4.043
4 0.410 1.069 5.149 0.318 0.409 0.203 0.403 0.269 0.252 0.152 0.224 2.309
5 0.415 2.114 3.506 0.337 0.419 0.208 0.321 0.206 0.192 0.153 0.440 1.698
6 0.407 1.316 2.369 0.303 0.797 0.413 0.282 1.274 0.179 0.163 1.142 1.430
7 0.393 1.123 2.262 0.294 0.431 0.531 0.250 0.669 0.174 0.531 0.670 1.655
8 0.395 1.000 1.358 0.244 0.464 0.280 0.232 0.336 0.178 1.117 1.163 10.220
9 0.425 0.933 1.144 0.277 0.419 0.203 0.224 0.246 0.165 1.082 10.390 5.495
10 0.398 2.668 1.025 0.275 0.462 0.223 0.210 0.199 0.166 0.820 5.403 9.025
11 0.388 2.589 1.025 0.266 0.386 0.293 0.211 0.190 0.173 1.031 2.704 4.807
12 0.457 4.646 0.979 0.255 0.331 0.223 0.198 0.191 0.259 0.934 1.238 2.707
13 0.574 5.132 0.906 0.256 0.293 0.239 0.194 0.189 0.201 0.503 0.851 1.907
14 0.561 2.683 0.795 0.262 0.278 0.232 0.214 0.178 0.168 0.560 0.668 1.544
15 0.487 1.731 0.720 0.267 0.273 0.202 0.183 0.174 0.177 1.646 0.864 1.363
16 0.448 1.868 0.666 0.246 0.287 0.196 0.182 0.164 0.169 0.841 1.021 1.243
17 0.498 5.067 0.635 0.255 0.333 0.269 0.188 0.180 0.138 0.482 0.948 1.268
18 0.606 8.582 0.637 0.245 0.330 0.274 0.187 0.149 0.155 0.385 7.739 10.760
19 0.968 5.663 0.621 0.241 0.382 0.312 0.201 0.162 0.221 0.296 6.231 5.222
20 0.797 4.796 0.509 0.233 0.504 0.563 0.174 0.156 0.210 0.264 7.207 2.862
21 0.687 2.705 0.528 0.238 0.406 0.672 0.177 0.155 0.175 0.236 4.765 1.851
22 2.104 2.188 0.478 0.240 0.334 1.696 0.174 0.155 0.168 0.227 4.033 1.960
23 2.956 2.050 0.503 0.227 0.302 1.064 0.170 0.160 0.162 0.223 4.490 3.794
24 1.529 8.257 0.488 0.220 0.266 0.492 0.170 0.152 0.155 0.221 2.514 10.770
25 1.068 13.810 0.453 0.242 0.235 0.778 0.176 0.661 0.152 0.248 1.630 8.671
26 0.857 7.915 0.439 0.299 0.232 1.273 0.228 0.273 0.151 0.249 1.398 4.859
27 0.754 3.537 0.433 0.301 0.231 1.789 0.206 0.274 0.166 0.225 3.324 2.919
28 0.655 2.574 0.395 0.267 0.220 1.221 0.186 0.499 0.155 0.222 11.510 2.068
29 0.619 0.358 0.263 0.210 0.667 0.166 0.466 0.153 0.198 4.399 1.812
30 0.581 0.350 0.248 0.216 0.527 0.248 0.848 0.154 0.190 2.494 2.483
31 0.547 0.348 0.201 0.203 0.374 0.184 5.837
Average 0.717 3.488 1.131 0.272 0.337 0.521 0.239 0.309 0.181 0.447 3.002 3.988
Lowest 0.388 0.524 0.348 0.220 0.201 0.193 0.166 0.149 0.138 0.147 0.185 1.243
Highest 2.956 13.810 5.149 0.350 0.797 1.789 0.538 1.274 0.268 1.646 11.510 10.770
Monthly total
(million cu m) 1.92 8.44 3.03 0.70 0.90 1.35 0.64 0.83 0.47 1.20 7.78 10.68
Runoff (mm) 14 61 22 5 7 10 5 6 3 9 56 77
Rainfall (mm) 20 93 16 7 44 113 22 80 16 83 139 104
Statistics of monthly data for previous record (May 1970 to Dec 1996----incomplete or missing months total 0.1 years)
Mean Avg. 4.122 2.803 2.144 1.644 0.978 0.632 0.343 0.351 0.590 1.723 2.355 3.113
flows: Low 0.528 0.689 0.418 0.277 0.223 0.131 0.138 0.078 0.161 0.150 0.167 0.492
(year) 1992 1981 1993 1976 1976 1976 1976 1976 1971 1972 1978 1971
High 10.770 9.828 4.413 3.829 3.313 3.054 1.274 1.618 5.443 11.580 10.030 7.022
(year) 1988 1990 1981 1983 1981 1971 1991 1985 1974 1987 1974 1993
Runoff: Avg. 79 49 41 31 19 12 7 7 11 33 44 60
Low 10 12 8 5 4 2 3 2 3 3 3 9
High 207 171 85 71 64 57 25 31 102 223 187 135
Rainfall: Avg. 89 54 64 53 52 53 47 55 71 83 84 85
Low 16 7 7 4 3 8 12 2 13 9 15 19
High 183 138 127 110 115 147 103 155 201 224 209 167
Summary statistics Factors affecting runoff
1997
For 1997 For record As % of $ Augmentation from effluent returns.
preceding 1997 pre-1997
Mean flow 1.203 1.730 70
Lowest yearly mean 0.589 1973
Highest yearly mean 2.845 1974
Lowest monthly mean 0.181 Sep 0.078 Aug 1976
Highest monthly mean 3.988 Dec 11.580 Oct 1987
Lowest daily mean 0.138 17 Sep 0.051 8 Aug 1983
Highest daily mean 13.810 25 Feb 64.770 2 Oct 1993
10% exceedance 3.128 3.860 81
50% exceedance 0.397 0.572 69
95% exceedance 0.160 0.148 108
Annual total (million cu m) 37.94 54.60 69
Annual runoff (mm) 273 393 69
Annual rainfall (mm) 737 790 93
{1961-90 rainfall average (mm) 806}
Station and catchment description
Asymmetrical compound Crump profile weir (crests: 4.0m and 6.0m broad). Crest tapping not currently used; over-estimation
of high flows (structure drowns frequently); but post-1995 flows truncated at c15 cumecs. Stilling well leakage can
influence water levels. Limited impact of artificial influences on runoff - small net augmentation due to sewage
effluent, which can significantly affect low flow patterns.
Principally an impervious (Weald Clay) catchment - mainly rural but includes Horsham.
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