"Tidal Wave" (caused by heavy rain) progressing 60 miles down the Dorset Stour in 35 hours through Milton-Gillingham-Hammoon-Blandford- Bear Mead-Wimborne-Ensbury-Throop Remove cattle and sheep from Eyemead, phone **** See also Dorset Stour Catchment Flood Management Plan by Environment Agency (Summary Report December 2009) Locations: Colesbrook (ST 807 278) | Hammoon (ST 820 147) | Loverley (SU 006 085) | Walford (SU 008 007) | Throop (SZ 113 958) | Hurn Court (SZ 126 969) |

Travel delays

Rain= -7 hrs 3298 Wincanton=0 hrs 3297 Milton on Stour=0 hrs 3296 Gillingham=+2 hrs 3306 Hammoon=+19 hrs 3305 Blandford=+23 hrs (3299 Walford Mill=+2 hrs) 3302 Wimborne=+2 and +30 hrs [Double surge (Allen then Stour) with Canford sluice lowered in between] 3295 Ensbury=+6 and +34 hrs 3303 Throop=+7 and +35 hrs

Travel times

The spread of travel times along the Dorset Stour. Moving peaks are first seen at Gillingham. Environment Agency advise:"Travel time in rivers is a combination of factors particularly the roughness (Mannings n) which is a factor of vegetation growth etc... The first event December 13th was the first big 'flush' of the season. This is likely to have flushed away a lot of dead or dying vegetation reducing frictional losses (Mannings n) shortening the travel time."

Recording Stations along Dorset Stour (run by Environment Agency) used in this report.

Manning's formula for Stream Flow V= n-1R2/3S1/2 V=mean velocity of flow, (metres per sec). n=Mannings coefficient of roughness. R=hydraulic radius (metres). S=slope of energy grade line (metres per metre). H=river height above AOD in metres. dH=fall along a section in metres. D=distance along river in kms. dT=travel time of peak along the section in hrs. Section H dH D kms dT V S R Gillingham 68.11 27.21 34.0 23 0.41 1249 3.2 Hammoon 40.9 9.9 17.32 10 0.48 1749 8.5 Blandford 31 13.0 19.18 8 0.67 1475 13.5 Bear Mead 18 3.39 5.2 2 0.72 1534 9.2 Wimborne 14.61 4.61 11.14 6 0.52 2416 10.5 Ensbury 10 5.0 5.46 1 13.8 Throop 5 ------ ----- ----- --- ---- ---- ---- 63.11 92.30 50 0.51 1462 10.5

Method of Prediction

METHOD Get time and height of a significant surge peak from Environment Agency website for Gillingham Choose a curve from Travel Times graph which matches the new surge peak, based on: Height of peak at Gillingham | Time before last good rainfall | Season of year (vegetation) | Suddenness of rain | Direction of rain. Apply delays on chosen curve to places downstream: Hammoon-Throop to make prediction. Follow the surge downstream using the EA website to correct and update your predictions.

DATA-1 STOUR peak heights (metres) & surge delays (hours) 2011 13dec 16dec 31dec 01jan 03jan 24jan 05feb 10feb 04mar Place 01 02 03 04 05 06 07 08 09 Gill 1.28 0.72 0.58 0.52 1.02 0.56 0.42 0.39 0.75 22 16 18 15 22 19 12 18 16 Hamm 2.56 1.71 0.52 0.81 2.30 0.55 0.52 0.46 1.51 11 6 5 6 6 7 4 5 5 Blan 1.09 0.87 0.65 0.71 1.01 0.59 0.85 0.52 0.57 7 7 7 5 5 8 6 6 8 BM 282 230 190 ? 260 170 230 ? 170 2 2 2 1 1 2 1 2 3 Wimb 0.96 0.76 0.72 0.75 0.96 0.66 0.76 0.61 0.65 7 3 3 5 6 2 4 6 2 Ensb 2.07 1.55 1.00 1.13 1.93 0.75 1.41 0.55 0.69 1 1 3 1 2 2 1 1 3 Thro 0.91 0.78 0.63 0.67 0.87 0.56 0.75 0.52 0.56 Tot [50] [35] [38] [33] [42] [32] [33] [38] [32] DATA-2 STOUR peak heights (metres) and surge delays (hours) 25apr 29apr 01may 10may 07jun 11jun 15jun 22jun 24jun 2012 11 12 13 14 15 16 17 18 19 Place 1.33* 1.42* 1.40* 0.58 0.65 0.56 1.08 0.68 0.86 Gill 6 15 19 7 19 22 13 13 17 3.02* 2.98* 2.82* 1.37 1.39 2.34 0.63 1.51 1.71 Hamm 9 8 9 5 6 7 5 5 5 1.87* 1.85* 1.47* 0.86 0.81 1.09 0.68 0.87 0.92 Blan 22 21 15 5 6 8 8 8 8 360* 376* 360* 244 225 282 193 237 246 BM 5 4 5 2 4 4 4 1 2 1.34* 1.40* 1.26* 0.84 0.80 0.94 0.70 0.84 0.90 Wimb 9 7 6 4 5 6 4 4 4 2.88* 2.95* 2.80* 1.63 1.59 2.18 1.26 1.60 1.85 Ensb 3 6 5 2 1 2 1 1 1 1.25* 1.31* 1.19* 0.82 0.69 0.87 0.62 0.73 0.77 Thro [54] [61] [59] [25] [43] [49] [35] [32] [37] Tot DATA-3 STOUR peak heights (metres) & surge delays (hours) 2012 04jul Place 20 21 22 23 24 25 26 27 28 Gill 0.91 21 Hamm 1.67 5 Blan 0.91 9 BM 244 2 Wimb 0.90 5 Ensb 1.87 2 Thro 0.76 Tot [44] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] DATA-4 STOUR peak heights (metres) and surge delays (hours) 2012 31 32 33 34 35 36 37 38 39 Place Gill Hamm Blan BM Wimb Ensb Thro [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] Tot

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