River Wylye Analysis and Modelling of Phosphates
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-S o u th w e s t/aasa FAUl. 5.< YSo^ River Wylye Analysis and Modelling of Phosphates Celia Bartlett & Neil Murdoch May 1998 1 IN T R O D U C T IO N .......................................................................................................... 1 1.1 Background ..............................................................................................................1 1.2 Objectives .................................................................................................................. 1 2 UPPER HAM PSHIRE AVON RIVER SYSTEM ......................................................2 2.1 Location .................................................................................................................... 2 2.2 Point Source Discharges ....................................................................................... 2 2.3 Routine Monitoring Sites ..................................................................................... 3 3 DATA A N A L Y S IS ................................................................................................................ 4 3.1 Selected Data ............................................................................................................ 4 3.1.1 D isch arges..................................................................................................... 4 3.1.2 Tributaries ...................................................................................................4 3.1.3 D eterm inand.................................................................................................4 3.1.4 W ater Quality Monitoring ..................................................................... 5 3.1.5 River F lo w s................................................................................................... 5 3.2 Seasonal and Longitudinal Variations in Phosphate Concentrations ... 6 3.3 Concentrations and Loads - Annual and S u m m er.........................................8 3.3.1 C oncentrations............................................................................................8 3.3.2 L o a d s ............................................................................................................ 14 4 ' M ODELLING ......................................................................................................................20 4.1 A im s .............................................................................................................................20 4.2 M odel Components ...............................................................................................20 4.2.1 D isch arges................................................................................................... 20 4.2.2 Tributaries ................................................................................................. 20 4.2.3 Gauging Stations ......................................................................................21 4.2.4 Calibration and V a lid ation ................................................................... 22 4.2.5 M odelling Scenarios.................................................................................24 5 SUM M ARY and CONCLUSIONS ...............................................................................26 © Environment Agency NATIONAL LIBRARY & INFORMATION SERVICE SOUTH WEST REGION Manley House. Kestrel Way. Exeter EX2 7LQ River Wylye_________________ Draft Model Report 1 INTRODUCTION 1.1 Background This report was written as part of an ongoing study of the Upper Hampshire Avon catchment initiated in response to concerns raised by English Nature about the levels of phosphates in this area. Statutory requirements which may enable the Agency to control phosphate levels are the Urban Waste Water Treatment Directive and the Habitats Directive. The UWWTD can be used to force nutrient stripping at PLC STW discharges if appropriate qualifying conditions are met. The Habitats Directive has been recently introduced and is designed to protect flora and fauna in designated areas. So far, in the Hampshire Avon catchment, Salisbury STW is to have nutrient stripping applied so as to ameliorate the phosphate levels in the lower Avon. This was done under the UWWTD regulations. Other discharges in the catchment which come under the scope of the UWWTD are Christchurch STW and Warminster STW, the latter being situated on the River Wylye. This report is concerned with the River Wylye from its source near Kingston Deverill south of Warminster to its confluence with the Nadder at Wilton. It is known, in general terms, that diffuse and point sources contribute to phosphate levels in the river. Diffuse sources arise from runoff from agricultural land* A rule of thumb appears to be that about 1 % of phosphates put onto the land will find its way into the river. Point sources may be large or small; the large ones being the PLC STWs. The purpose of this report is to examine in some detail the point source contributions to phosphate levels in the Wylye. The intention is to provide information on which decisions about management of the catchment may be based, but not to make those decisions. 1.2 Objectives The objectives are to: A determine the spatial and temporal trends of phosphate concentrations along the River Wylye B quantify the seasonal and annual in-river and discharge phosphate loads C perform discharge modelling to quantify the impact of nutrient stripping 20th May 1998 1 C Bartlett & N Murdoch EA S W River Wylye Draft Model Report 2 UPPER HAMPSHIRE AVON RIVER SYSTEM 2.1 Location The major rivers of the Upper Hampshire Avon catchment are shown below: 2.2 Point Source Discharges The map below shows the monitored discharges in the upper Avon catchment. 20th May 1998 2 C Bartlett & N Murdoch EA SW River Wylye Draft Model Report 2.3 Routine Monitoring Sites The map below shows the river sites routinely monitored in the upper Avon catchment. 20th May 1998 3 C Bartlett & N Murdoch EA SW River Wylye Draft "Model Report 3 DATA ANALYSIS 3.1 Selected Data The present analysis is restricted to the River Wylye, which is shown schematically in Figure 4 from Kingston Deverill to its confluence with the River Nadder. 3.1.1 Discharges The main discharge to the River Wylye is from Warminster STW. Other larger discharges include those from Hurds (Hill Deverill) Fish Farm, Bishopstrow Fish Farm and Great Wishford STW - details of all these are given below. Discharge URN Flow (m3/s) 0) Hurds Fish Farm 30117000 0.11 (MAX) Warminster STW 41406900 0.03 (DWF) Bishopstrow Fish Farm 30135000 0.16 (MAX) Gt Wishford STW 41415900 0.01 (DWF) Table 1 (1) These values are taken from the associated discharge consents 3.1.2 Tributaries The tributaries considered are shown below. In the. case of the Were tributary the monitoring point 30131000 - Were Calveswater - has not been sampled since October 1995 and there is some uncertainty about its location; the concentration levels of phosphate at this URN are relatively high, perhaps indicating some influence from Warminster STW. Tributary URN MeanFlow (m3/s)(2) Shear Water 30179000 0.136 Were 30131000 0.19 Chitteme Brook 30138000 0.668 Till River 30146000 0.896 Table 2 (2) These values are derived from the program Micro Low Flows. 3.1.3 Determinand The determinand studied is ortho-phosphate, which has determinand code number 0180. 20th May 1998 4 C Bartlett & N Murdoch EA SW Figure 4: River Wylye Diagrammatic representation of Point Discharges and Routine Monitoring Points KEY WARMINSTER 38.9km Distance downstream from Kingston Dewrtfl 10km y ' B e ra tn nia B1S9680Q (DWP"ft.4) N — ► ^jlril discharge JScrahvnBr 30133000 (MF-1.57B) • Routine Monitoring F^lnt (tarton S1476000 <«000) QUASAR_TRIB1 MF ■rmcnLkXa 81900800 (<1Q),eo*mny 1 (&JoaorFVw= 257) MIcrolowFlow* Mean Flow (ml/s) amrtbro<* 30100000 (MF-1.S7B) WERE_TRIB MFGS MIcroLowFlows Mean Flow for Gouging Station (ml/s) BbtKDrtrew Mtl 50134000 (MF-1.58*) ADF Gauged Awrege Deify Flow for GS (m3/s) (MF=\19: Qua«ariTcMP.399) FFerm 30115000 (<13«0<J) ' ~ (IrM OWmm>u»» FFvm 30138100) DWF Consented Dry Weather Flow (m3/d) ufcW «C onf 30148000(MF-1.S7) * 0.1km FB 30130000 <Mf=" 1.593; HurtmUo«nS1B7MOO(«11) <15 Indicates Maximum Flow of 15 ml/d HaiftrdMir* 30130000 (MF»1,37) jl S.Okn A Gauging Station WBrmhistar STW 41406900 / © Node used in QUASAR model Quasar Flow Accreted now used in QUASAR model (ml/s) u/»Wm*wt»STW 30129000 <MF*1.37) C?) JobeMB 31848900 (noOo talk) Pnv^nt D'TOKOT n»: A0F=t SHEAR WATER 30127000 (MF-1. QLMSAR_7"R/02 (QuaBaf l ow^ ,96l) <MF=.130. Qu9MtRow=194) ButonVmr 91026900 (*8.4) M M I 30120000 <MF“ 1.177) Crock vton 50176000 CHITTERNE BROOK (MFs.668; OJowrFVw=.663) Shearwater Conf 30170000’ HgytMtaay, W w l H i 31623901 (M l 1-1 3 .8 ) CNtorne, AM mOo 31441900 TILL RIVER htayMury, BUcftnrtte* 31630900 (*13,8) <<«>. (MFi.896; Onwu*fk*«= 1.568) Tleheetf 41420000 KhookCnv 31476900 (<90) V.^<i8£km (DWPNiie).i LmoB0130123000<MF«1.0B2) f 6.3871 utimostw smiooo («is> HgpyBrtg A3B 31879900 (<30). eaafcawy ^ 3 a m BSOOSBr 3012 10 0 0 (M F»1 .062) f 4 Han C od M , HriAHo. 91474000 (4.S), (toavaPH 31643900 (<V) Ohrwrton 41412900 (1W W III Hunj» C m s Bede and Pith Farm M C m M i 3012Q200 (MF-1.092) (Ufl Inn WO*** 31P76900 <<8.0 HQIDvCraMtMdt 97TMCT1/2000 HufdeGnMbede SO1402MMOO CM_Q« m TM i 37043000 (*14790) Ptou^i.Stodrten 81076M0 (<10^, M tknny • (<&79*<4779*<n73) (u/« and d/i Cham* 3014410*200) Um4owU— 91S30900 (<14) >30120100 (MF-V082) f I S k m HWEMTafm 30117D00 (<0100) »127200(UP-4 077) BemtckBUamee 41420900 (tW