modelling flow pathways, sediment and phosphorus fluxes in ......• pbc: event dynamics appear to...

School of Engineering

Modelling flow pathways, sediment and phosphorus fluxes in two contrasting headwater catchments using high frequency monitoring data

Dr Russell Adams, Dr Paul Quinn, Dr Nick Barber


What are “Demonstration Test Catchments”?

• DTC =‘Catchment scale experiment to evaluate policy tools’ across 3 catchments in UK.

• ‘Evidence based evaluation of policy tools’

• ‘Observatory’• Integration of datasets • To serve Policy & Science• Is it possible to reduce the impact of

agricultural diffuse water pollution cost-effectively while maintaining food security?


Mains power

Ammonium analyser

PumpMeteor telemetry unit

Flow cell

YSI multi-parameter sonde

Total P and Total reactive P analyser

Nitrate probe

ISCO automatic water sampler

LHS view RHS view

High specification kiosks


• The CRAFT runs over the entire Newby Beck Catchment (12.5 km2) and entire Pow Beck Catchment (10.4 km2)

• Similar land-use and climate.

• Different soils and geology• Farming more intensive in

PBC (pigs, poultry etc)

Case Study Overview: Newby Beck & Pow Beck (Eden DTC)


Catchment Runoff Attenuation Flux Tool (CRAFT)Overview

• Flow and nutrient pathways informed by data

• Lumped model with constant Cs in Fast S/S and Slow G/W Pathways, C vs. Q in SR (linear)

• Attenuation can be added to SR pathway, will be used later on…. CRAFT can also remove sediments and particulate nutrients by trapping.

DYNAMIC SURFACESTORE SS

SPLIT

DYNAMIC SOILSTORE SSS

DYNAMICGROUNDWATERSTORE SGW

Rainfall AET

TrapPP, TRP & TSS

SR ATTENUATION STORE SATT

Outlet(Loads and FlowsCombined)

SR

FAST S/S

SLOW G/W


Modelling Overview

• We make use of high resolution data to inform model structure and processes• Many approaches to calibration: Deterministic (“Expert”) vs. full uncertainty

analysis (e.g. GLUE) • Multi-objective criteria. What to use (Flow, Loads, Concentrations , or

a combination of these)?• Validation important too and often overlooked with nutrient models• What’s Important in a model? High flows and loads during events obviously?• Model must inform policy makers in terms of mitigation options down the line


NBC: NSE = 0.79

NBC Observed & Modelled Q plus rainfall (blue)Period 1, calibrationValidation (Period 2) NSE = 0.76

See Adams et al. (STOTEN , 2016) for more details

Modelling Results: 1. NBC – “Expert”0

10

20

300.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

01-Apr-12 21-May-12 10-Jul-12 29-Aug-12

Rai

nfal

l (m

m/h

r)

Q (m

m/h

r)

Obs Mod RainEvents in dashed red ovals areanalysed in more detail

NBC: NSE = 0.79


Modelling Results: 2. PBC -”Expert”

0

10

20

300.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

01-Apr-12 21-May-12 10-Jul-12 29-Aug-12

Rai

nfal

l (m

m/h

r)

Q (m

m/h

r)

Obs Mod RainPBC: NSE = 0.78

PBC: has reasonably similar hydrologicalresponse over these periods to NBC.The CRAFT was recalibrated witha good fit to Q although some overestimation in calibration period.

PBC Observed & Modelled Q plus rainfall (blue) Period 1, calibrationValidation (Period 2) NSE = 0.75


Modelling Results 3:Phosphorus: Single Event at NBC(Multi Objective)

Introduces uncertainty which is popular! Shaded area bounded by 5th and 95th modelled concentration.Blue line shows observed concentrations. Needsuncertainty bounds too due to measurement/equipment errors?

Observed


0

0.1

0.2

0.3

0.4

0.5

0.6

-25%

-20%

-15%

-10%

-5%

0%

5%

10%

15%

20%

25%

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

NSE ()

-Load Error (%)

NBC

LE(TP) NSE

Modelling Results 3: Example of Multi-Objective calibration (for TP)

KSR(PP) Parameter(gives concentration of PP in Surface Runoff Pathway CSR(PP) = qSR x KSR(PP))

High Parameter values overpredicts TP Load and NSETends to zero

“Expert” value 0.9 informed bymultiple simulations

1. NSE (TP Concentration) >=02. Load Error (TP) < ± 20%20000 Model Runs


012345678910

0

5

10

15

20

25

30

28-Jun-12

29-Jun-12

30-Jun-12

P (T

RP

) Lo

ad (k

g/hr

)

P (T

P &

TU

P)

Load

(kg/

hr) Obs TPL

TPL

TUPL

TRPL

TRP(SS)L

NBC

• NBC: Observations indicate flashy TP dynamics with sharp peak in load, rapid decrease follows.• PBC: Event dynamics appear to be different to NBC, more lag observed in TP load • Most of the TP in the NBC is in the form of TUP (i.e. particulate)

The TRP load in the fast S/S pathway is about 5 times greater in the PBC than in the NBC during this event

0

1

2

3

4

5

6

7

8

9

10

0

5

10

15

20

25

30

28-Jun-12

29-Jun-12

30-Jun-12

P (T

RP

) Lo

ad (k

g/hr

)

P (T

P &

TU

P)

Load

(kg/

hr)

Obs TPL

TPL

TUPL

TRPL

TRP(SS)L

PBC

Modelling Results 4:Phosphorus: Loads P Loads are important. When planning Mitigation Measures to reduce them, Surface Runoff pathway is easiest to targetCRAFT supplies loads by flow pathway. Plots show Fast S/S load and total load from model (TP & TRP) and Observed TP Load


Modelling Results 5: Suspended Sediment (SS)

• NBC: Left pane, SS and TP event dynamics are similar. Model response more damped. • PBC: Right pane, small event in terms of SS export from Pow. Fast S/S component higher than in NBC for this

event but SR component lower

0

50

100

150

200

250

300

350

400

0.0E+00

2.0E+03

4.0E+03

6.0E+03

8.0E+03

1.0E+04

1.2E+04

1.4E+04

1.6E+04

28-Jun-12

29-Jun-12

30-Jun-12

01-Jul-12

Mod

TS

S L

oad

(Fas

t S/s

) (kg

/hr)

TSS

Load

(kg/

hr)

TSSL

Obs TSSL

TSS(SS)L

NBC

0

50

100

150

200

250

300

350

400

0.0E+00

2.0E+03

4.0E+03

6.0E+03

8.0E+03

1.0E+04

1.2E+04

1.4E+04

1.6E+04

28-Jun-12

29-Jun-12

30-Jun-12

01-Jul-12

TSS

Loa

d (F

ast S

/S) (

kg/h

r)

TSSL

Obs TSSL

TSS (SS)L

PBC

SS Loads are important. When planning Mitigation Measures to reduce them, Surface Runoff pathway easiest to targetCRAFT supplies loads by flow pathway, here we show Fast S/S load and total load


0

100

200

300

400

500

600

TSS

Yiel

d (k

g/ha

/yr )

SR

Fast S/S

Slow G/W

PBC Period 1

Modelling Results 6:Smart Export Coefficients

0.0

0.5

1.0

1.5

2.0

2.5

3.0

TRP TP

Yiel

d (k

g/ha

/yr P

)

Slow G/W Fast S/S SR

NBC Period 1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

TRP TP

Yiel

d (k

g/ha

/yr P

)

PBC Period 1

0

100

200

300

400

500

600

TSS

Yiel

d (k

g/ha

/yr )

Modelled SS Transport PathwaysSlow G/W Fast S/S SR

NBC Period 1


Conclusions

• The two catchments are hydrologically similar (runoff)• Flow pathways and P export differ (PBC > NBC in terms of TRP)• Fast subsurface pathway in PBC equally important too (For PP and SS)• Variability in “Smart” export coefficients quite high• Mitigation options in PBC may be focussed on drain flow and soils to

target SRP as well as particulates?• High-resolution data enables detailed forensics of event P dynamics• Our capability to model hourly concentrations unmatched by other

models to date.


Thank you!

modelling flow pathways, sediment and phosphorus fluxes in ......• pbc: event dynamics appear to...

Documents