OR/13/031 Material and methods - Revision history

Ajhil: /* Meteorological and gauged river flow data */

2021-10-19T08:16:27Z

Meteorological and gauged river flow data

← Older revision		Revision as of 09:16, 19 October 2021
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	[[Image:OR13031fig6.jpg\|thumb\|center\|400px\| '''Figure 6'''    Distributed mean daily precipitation in the Nene Catchment, averaged over the period 1962–2001. ]]		[[Image:OR13031fig6.jpg\|thumb\|center\|400px\| '''Figure 6'''    Distributed mean daily precipitation in the Nene Catchment, averaged over the period 1962–2001. ]]

	[[Image:OR13031fig7.jpg\|thumb\|center\|~~500px~~\| '''Figure 7'''     Gauged river flow data for the Orton (Blue) and Upton (red) stations. Note the differing flow scales on the vertical axis. ]]		[[Image:OR13031fig7.jpg\|thumb\|center\|700px\| '''Figure 7'''     Gauged river flow data for the Orton (Blue) and Upton (red) stations. Note the differing flow scales on the vertical axis. ]]

	For the calibration, a daily cycle of model output was specified for the calculation of groundwater level (mAOD), base flow (m<sup>3</sup> day<sup>-1</sup>), recharge (m<sup>3</sup> day<sup>-1</sup>) and surface water (m<sup>3</sup> day<sup>-1</sup>). To assess the errors associated with differing water flow routes, and to simplify the process, time series of simulated groundwater and surface flow were calibrated to observed data separately. The first phase of calibration removed the simulated base flow component from surface flows. These where compared to a base flow separated flow records from the Orton and Upton gauging stations for the surface component analysis. Once an acceptable agreement was achieved, the second phase of calibration was implemented, where the base flow component was re-instated in the simulation and a comparison to the non-separated gauged river flow dataset used for analysis. The same river gauging stations were used for both phases of the calibration.		For the calibration, a daily cycle of model output was specified for the calculation of groundwater level (mAOD), base flow (m<sup>3</sup> day<sup>-1</sup>), recharge (m<sup>3</sup> day<sup>-1</sup>) and surface water (m<sup>3</sup> day<sup>-1</sup>). To assess the errors associated with differing water flow routes, and to simplify the process, time series of simulated groundwater and surface flow were calibrated to observed data separately. The first phase of calibration removed the simulated base flow component from surface flows. These where compared to a base flow separated flow records from the Orton and Upton gauging stations for the surface component analysis. Once an acceptable agreement was achieved, the second phase of calibration was implemented, where the base flow component was re-instated in the simulation and a comparison to the non-separated gauged river flow dataset used for analysis. The same river gauging stations were used for both phases of the calibration.
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	Following the first phase of calibration, there is an acceptable match between simulated and observed river flows with the base flow component removed (see Figure 8 for the comparison at the Orton gauging station). The timing of large flow discharge events shows excellent agreement; however, the representation of peak discharge values is not as good. The disparity most likely arises from the misrepresentation of true rainfall and surface frictional characteristics under the current discretisation scheme, and would be improved with input data at a higher spatial resolution. Although the peak discharges are not fully represented in the simulation, the average peak discharge value is very similar to the observed value. Following the second phase of calibration, where base flow is introduced, the match between simulated and observed river flows is in some places poor (Figure 9). The worst representation occurs during recession of the river, where groundwater recession rates are not fully representative of the system. This suggests that the parameterisation of the groundwater model is not accurate. However, the simulated peak flow values show close agreement with the observed values. For this study the latter is the most important attribute of the calibrated output, as it is during these periods where the majority of sediment is transported.		Following the first phase of calibration, there is an acceptable match between simulated and observed river flows with the base flow component removed (see Figure 8 for the comparison at the Orton gauging station). The timing of large flow discharge events shows excellent agreement; however, the representation of peak discharge values is not as good. The disparity most likely arises from the misrepresentation of true rainfall and surface frictional characteristics under the current discretisation scheme, and would be improved with input data at a higher spatial resolution. Although the peak discharges are not fully represented in the simulation, the average peak discharge value is very similar to the observed value. Following the second phase of calibration, where base flow is introduced, the match between simulated and observed river flows is in some places poor (Figure 9). The worst representation occurs during recession of the river, where groundwater recession rates are not fully representative of the system. This suggests that the parameterisation of the groundwater model is not accurate. However, the simulated peak flow values show close agreement with the observed values. For this study the latter is the most important attribute of the calibrated output, as it is during these periods where the majority of sediment is transported.

	[[Image:OR13031fig8.jpg\|thumb\|center\|~~500px~~\| '''Figure 8'''    Base flow separated surface runoff derived from the Orton gauged river flow dataset (blue) compared to the simulated runoff (red) from 1970–1979. These datasets were used to calibrate the surface flow characteristics of the CDP. ]]		[[Image:OR13031fig8.jpg\|thumb\|center\|700px\| '''Figure 8'''    Base flow separated surface runoff derived from the Orton gauged river flow dataset (blue) compared to the simulated runoff (red) from 1970–1979. These datasets were used to calibrate the surface flow characteristics of the CDP. ]]

	[[Image:OR13031fig9.jpg\|thumb\|center\|~~500px~~\| '''Figure 9'''    Surface flow (m<sup>3</sup> s<sup>-1</sup>) from the Orton gauged river flow dataset (blue) compared to the simulated runoff (red) from 1970–1979. These datasets were used to calibrate the groundwater surface flow characteristics of the CDP. ]]		[[Image:OR13031fig9.jpg\|thumb\|center\|700px\| '''Figure 9'''    Surface flow (m<sup>3</sup> s<sup>-1</sup>) from the Orton gauged river flow dataset (blue) compared to the simulated runoff (red) from 1970–1979. These datasets were used to calibrate the groundwater surface flow characteristics of the CDP. ]]

	===Simulation projection===		===Simulation projection===

Ajhil: /* Water partitioning */

2021-10-19T08:15:46Z

Water partitioning

← Older revision		Revision as of 09:15, 19 October 2021
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	====Water partitioning====		====Water partitioning====
	The partitioning of rainfall between, evaporation, runoff and recharge to groundwater in the CDP is achieved using a soil water balance model (Wang et al., 2012<ref name="Wang 2012">Wang, L, Barkwith, A, Jackson, C R, and Ellis, M A. 2012. SLiM: an improved soil moisture balance method to simulate runoff and potential groundwater recharge processes using spatio-temporal weather and catchment characteristics. 12th UK CARE Annual General Meeting, UK Chinese Association of Resources and Environment, Bristol, UK, 8 Sept 2012.</ref>). We implement a simple technique that represents potential groundwater recharge and runoff processes based on spatio- temporally distributed soil moisture conditions. Soil moisture is a function of; rainfall, potential evapotranspiration, soil moisture condition, topography, soil types, crop type and base flow index (BFI). The method we use represents these soil water processes responding to variable soil water storage properties (see Rushton, 2003<ref name="Rushton 2003">Rushton, K R. 2003. Groundwater hydrology: conceptual and computational models. John Wiley and Sons Ltd, West Sussex, England.</ref>) and vegetation growth stages (see Allen et al., 1998<ref name="Allen 1998">Allen, R, Pereira, L A, Raes, D, and Smith, M. 1998. Crop evapotranspiration: guidelines for computing crop water requirements. FAO, Irrigation and Drainage Paper No.56. FAO, Rome, Italy.</ref>). When soil moisture reaches field capacity and is unable to store further additions of water, water drains freely in the saturated soil. Additional water inputs to the soil result in lateral runoff (routed by Lisflood), if a gradient exists towards adjacent locations, and if required as percolation downwards through the saturated soil (groundwater recharge). If the rainfall intensity is greater than the capacity of soil to maintain infiltration, water accumulates on the soil surface and becomes surface runoff. Water not accounted for in soil storage, evapotranspiration or uptake by vegetation is termed excess water. Excess water is divided between runoff and recharge to groundwater based on a base flow index parameter. Base flow index is an average surface to subsurface water partitioning ratio reflecting the permeable nature of the catchment in addition to other catchment characteristics. The base flow index parameter is estimated, by performing a baseflow separation on a river flow time-series, and further refined through an iterative calibration process. In general, greater runoff and reduced recharge is observed in areas with steeper slopes. Consequently, average and nodal terrain gradient are factored into the calculation of recharge and runoff.		The partitioning of rainfall between, evaporation, runoff and recharge to groundwater in the CDP is achieved using a soil water balance model (Wang et al., 2012<ref name="Wang 2012">Wang, L, Barkwith, A, Jackson, C R, and Ellis, M A. 2012. SLiM: an improved soil moisture balance method to simulate runoff and potential groundwater recharge processes using spatio-temporal weather and catchment characteristics. 12th UK CARE Annual General Meeting, UK Chinese Association of Resources and Environment, Bristol, UK, 8 Sept 2012.</ref>). We implement a simple technique that represents potential groundwater recharge and runoff processes based on spatio-temporally distributed soil moisture conditions. Soil moisture is a function of; rainfall, potential evapotranspiration, soil moisture condition, topography, soil types, crop type and base flow index (BFI). The method we use represents these soil water processes responding to variable soil water storage properties (see Rushton, 2003<ref name="Rushton 2003">Rushton, K R. 2003. Groundwater hydrology: conceptual and computational models. John Wiley and Sons Ltd, West Sussex, England.</ref>) and vegetation growth stages (see Allen et al., 1998<ref name="Allen 1998">Allen, R, Pereira, L A, Raes, D, and Smith, M. 1998. Crop evapotranspiration: guidelines for computing crop water requirements. FAO, Irrigation and Drainage Paper No.56. FAO, Rome, Italy.</ref>). When soil moisture reaches field capacity and is unable to store further additions of water, water drains freely in the saturated soil. Additional water inputs to the soil result in lateral runoff (routed by Lisflood), if a gradient exists towards adjacent locations, and if required as percolation downwards through the saturated soil (groundwater recharge). If the rainfall intensity is greater than the capacity of soil to maintain infiltration, water accumulates on the soil surface and becomes surface runoff. Water not accounted for in soil storage, evapotranspiration or uptake by vegetation is termed excess water. Excess water is divided between runoff and recharge to groundwater based on a base flow index parameter. Base flow index is an average surface to subsurface water partitioning ratio reflecting the permeable nature of the catchment in addition to other catchment characteristics. The base flow index parameter is estimated, by performing a baseflow separation on a river flow time-series, and further refined through an iterative calibration process. In general, greater runoff and reduced recharge is observed in areas with steeper slopes. Consequently, average and nodal terrain gradient are factored into the calculation of recharge and runoff.

	====Surface water routing====		====Surface water routing====

Ajhil at 08:15, 19 October 2021

2021-10-19T08:15:24Z

← Older revision		Revision as of 09:15, 19 October 2021
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	The river Nene is the UK’s 10th longest river and rises close to the village of Badby near Daventry, flowing in a north-easterly direction out to the Wash via the town of Northampton and City of Peterborough (Figure 1). It is 161 km long and has a catchment area of 2270 km<sup>2</sup>. The catchment for the upper six water bodies of interest in this study has an area of 1590 km<sup>2</sup>. The river is navigable from the sea as far as Northampton where it connects with the Grand Union Canal. The floodplain is relatively wide (from a few hundred meters to a couple of km) and the channel frequently bifurcates and rejoins (Williams & Fawthrop, 1988<ref name="Williams 1988">Williams, J J R, and Fawthrop, N P. 1988. A mathematical hydraulic model of the river Nene — a canalized and heavily controlled river. Regulated Rivers: Research and Management, 2, 517–533.</ref>; Meadows, 2007<ref name="Meadows 2007">Meadows, I. 2007. Hydrology. In Synthetic Survey of the Environmental Archaeological and Hydrological record for the River Nene from its source to Peterborough. eds. Allen, P, Boismier, W A, Brown, A G, Chapman, A, and Meadows, I. Northamptonshire Archaeology, Report PNUM 3453.</ref>). A major characteristic of the catchment is that the river generally has very slow flow. The river course falls from ~160 m AOD at source to ~6 m AOD at Peterborough. The majority of this fall occurs in the first 9.5 km, with the channel lying at 80 m AOD at Weedon (Meadows, 2007<ref name="Meadows 2007"></ref>). In the first section the river drops 1 m in 270 m and by the time it reaches Northampton it drops 1 m every 1500–2000 m and then by Thrapston it drops 1 m in every 3000 m (Meadows, 2007<ref name="Meadows 2007"></ref>).		The river Nene is the UK’s 10th longest river and rises close to the village of Badby near Daventry, flowing in a north-easterly direction out to the Wash via the town of Northampton and City of Peterborough (Figure 1). It is 161 km long and has a catchment area of 2270 km<sup>2</sup>. The catchment for the upper six water bodies of interest in this study has an area of 1590 km<sup>2</sup>. The river is navigable from the sea as far as Northampton where it connects with the Grand Union Canal. The floodplain is relatively wide (from a few hundred meters to a couple of km) and the channel frequently bifurcates and rejoins (Williams & Fawthrop, 1988<ref name="Williams 1988">Williams, J J R, and Fawthrop, N P. 1988. A mathematical hydraulic model of the river Nene — a canalized and heavily controlled river. Regulated Rivers: Research and Management, 2, 517–533.</ref>; Meadows, 2007<ref name="Meadows 2007">Meadows, I. 2007. Hydrology. In Synthetic Survey of the Environmental Archaeological and Hydrological record for the River Nene from its source to Peterborough. eds. Allen, P, Boismier, W A, Brown, A G, Chapman, A, and Meadows, I. Northamptonshire Archaeology, Report PNUM 3453.</ref>). A major characteristic of the catchment is that the river generally has very slow flow. The river course falls from ~160 m AOD at source to ~6 m AOD at Peterborough. The majority of this fall occurs in the first 9.5 km, with the channel lying at 80 m AOD at Weedon (Meadows, 2007<ref name="Meadows 2007"></ref>). In the first section the river drops 1 m in 270 m and by the time it reaches Northampton it drops 1 m every 1500–2000 m and then by Thrapston it drops 1 m in every 3000 m (Meadows, 2007<ref name="Meadows 2007"></ref>).

	[[Image:OR13031fig1.jpg\|thumb\|center\|~~500px~~\| '''Figure 1'''    Map of the sampling locations in each of the six water bodies of the River Nene referred to in this study. The symbols for each water body are colour coded to represent the ‘Ecological status’ for that water body (Green = good; Orange = moderate; Red = poor). ]]		[[Image:OR13031fig1.jpg\|thumb\|center\|700px\| '''Figure 1'''    Map of the sampling locations in each of the six water bodies of the River Nene referred to in this study. The symbols for each water body are colour coded to represent the ‘Ecological status’ for that water body (Green = good; Orange = moderate; Red = poor). ]]

	==Bedrock geology==		==Bedrock geology==
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	'''''Whitby Mudstone formation:''''' Medium and dark grey fossiliferous mudstone and siltstone, laminated and bituminous in part, with thin siltstone or silty mudstone beds and rare fine-grained calcareous sandstone beds. Dense, smooth argillaceous limestone nodules are very common at some horizons and phosphatic nodules are found at some levels. Nodular and fossiliferous limestones occur at the base in some areas.		'''''Whitby Mudstone formation:''''' Medium and dark grey fossiliferous mudstone and siltstone, laminated and bituminous in part, with thin siltstone or silty mudstone beds and rare fine-grained calcareous sandstone beds. Dense, smooth argillaceous limestone nodules are very common at some horizons and phosphatic nodules are found at some levels. Nodular and fossiliferous limestones occur at the base in some areas.

	[[Image:OR13031fig2.jpg\|thumb\|center\|~~500px~~\| '''Figure 2'''    Bedrock geology map of the main six water bodies of the River Nene based on the BGS 625k scale geological map. ]]		[[Image:OR13031fig2.jpg\|thumb\|center\|700px\| '''Figure 2'''    Bedrock geology map of the main six water bodies of the River Nene based on the BGS 625k scale geological map. ]]

	==Superficial geology==		==Superficial geology==

Dbk: 1 revision imported

2016-12-07T11:03:03Z

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← Older revision	Revision as of 12:03, 7 December 2016
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Ajhil: /* Estimating the annual mass of orthophosphate adsorbed/desorbed to each water body and across all water bodies */

2016-11-30T12:20:13Z

Estimating the annual mass of orthophosphate adsorbed/desorbed to each water body and across all water bodies

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