Tracing and tracking sediment sources in river catchments

Transcription

1 Insert image here Insert image here Tracing and tracking sediment sources in river catchments Adrian Collins and Yusheng Zhang Delivering the WFD 1

2 The sediment problem information on sediment SOURCES is urgently required to target mitigation options information on the EFFICACY of mitigation options is urgently required Understanding sediment sources 2

3 The measurement/monitoring problem 3

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5 The measurement/monitoring problem INDIRECT APPROACH - erosion mapping - surveying - profilometers - erosion pins/peep - GPS - photogrammetry - erosion plots - bounded / unbounded The measurement/monitoring problem DIRECT APPROACH - SEDIMENT TRACING 5

6 Sediment fingerprinting Sediment source classification 6

7 Spatial sources geological zones Spatial sources tributary subcatchments River monitoring sites 7

8 Spatial sediment sourcing dual-pronged sediment sampling instantaneous bed sediment remobilisation time-integrated sampling using retrievable baskets Generic sediment source types pasture topsoils cultivated topsoils damaged road verges channel banks/subsurface sources STWs 8

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10 Sediment source discrimination Sediment fingerprints high Source 1 single component Source 2 Concentration Source 3 Sediment low 10

11 Sediment fingerprints composite 11

12 Sediment source apportionment Revised numerical mass balance modelling particle size selectivity organic matter selectivity within-source variation in tracer properties tracer discriminatory power prior information on bank erosion inputs uncertainty in characterising input property values for sources and sediment combination of local and global optimisation tools 12

13 Revised uncertainty analysis random sampling with conventional statistics random sampling with robust statistics LHS sampling with conventional statistics LHS sampling with robust statistics pdfs for sources and sediment Histogram for Random Numbers

14 Local and global optimisation Date 29/10/02-19/11/02 19/11/02-17/12/02 17/12/02-7/01/03 7/01/03-4/02/03 4/02/03-11/03/03 11/03/03-3/07/03 Random start 5 out of out of out of out of out of out of 5000 Local start 12 out of out of out of out of out of out of

15 Local and global optimisation Sub-catchment Upper Axe Temple Brook River Synderford Blackwater River Kit Brook River Yarty Local start Select GA Y Y Y N Y Y Improving the resolution of sediment source information work to date provides generic information e.g. % input from grassland need to improve the resolution to assist mitigation targeting further 15

16 Higher resolution arable sources wheelings interwheelings cultivated fields pasture fields channel banks downstream suspended sediment load Higher resolution grassland sources poached gateways poached cattle tracks cultivated fields pasture fields channel banks downstream suspended sediment load wider poaching /pugging 16

17 Higher resolution bank sources poached banks natural fluvial scour cultivated fields pasture fields channel banks downstream suspended sediment load Coupling to CSF capital grant options 17

18 Sediment tracking labelling of target areas using synthetic tracers Sediment tracking 11,000 gauss magnets inserted in watercourses 18

19 Sediment tracking 19

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21 Biglands Bog: high resolution sources configurations of high risk in grassland wider poached areas poached cattle tracks poached gateways The approach conventional source fingerprinting particle tracking particle tracking 21

22 Biglands Bog: high resolution sediment sources % c o n trib u tio n grassland = ~75% total load 0 wider areas of hoofing damage poached cattle tracks poached gateways High resolution grassland sediment source High resolution arable and bank sources (River Glaven, Norfolk) arable = ~30% total load banks = ~35% total load % contribution wheelings inter-wheelings poached river banks natural river bank fluvial scour High resolution sediment source 22

23 Assessing the efficacy of sediment mitigation options Mitigation method effectiveness ID Mitigation Method Arable Clay Loam Sandy Loam Grass Clay Loam Sandy Loam 1 Convert arable land to extensive grassland Establish cover crops in the autumn Cultivate land for crop establishment in spring, not autumn Adopt minimal cultivation systems Cultivate compacted tillage soils Cultivate and drill across the slope Leave autumn seedbeds rough Avoid tramlines over winter Establish in-field grass buffer strips Loosen compacted soil layers in grassland fields Maintain and enhance soil organic matter levels Allow field drainage systems to deteriorate Reduce overall stocking rates on livestock farms Reduce the length of the grazing day or grazing season Reduce field stocking rates when soils are wet Move feed and water troughs at regular intervals Fence off rivers and streams from livestock Construct bridges for livestock crossing rivers and streams Re-site gateways away from high-risk areas Establish new hedges Establish riparian buffer strips Establish and maintain artificial (constructed) wetlands

24 Efficacy of river bank fencing 24

25 Insertion of basket samplers Insertion of basket samplers use of coloured string to mark inserted basket 25

26 Retrieval of basket samplers use of outer sleeve to prevent the winnowing of fine interstitial sediment during basket removal from the river bed 26

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28 Efficacy of river bank fencing success undermined by insertion of drinking bays Efficacy of river bank fencing success undermined by poor maintenance 28

29 Insert image here The Demonstration Test Catchment project Insert image here The project components 29

30 Experimental design Organic and inorganic sources in a single framework source apportionment of organic sources using fluorescenceexcitation-emissionspectra (EEMS) and PARAFAC analysis NIR reflectance TC, TN, TOC analysis bulk stable isotopes for 15 N and 13 C potential organic sediment sources agriculture slurries, manures damaged road verges (decaying vegetation) banks (decaying riparian and instream vegetation point sources (STWs / septic tanks 30

31 Mitigation options stream bank fencing improved maize management improved slurry storage improved cultivation timings feeder ring management Advantages of the developing framework applicable at a range of scales links inorganic, organic and high resolution sources to channels (not edge of field) encourages assessment of multiple sources / pollutants / configurations of risk contributor to weight of evidence on catchment scale sediment sources and mitigation option efficacy 31

32 THANK YOU! 32