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Introduction Tab
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Somerset Levels and
Moors Phosphorus Budget Calculator V2.1
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Following the
Dutch Nitrogen Case which ruled that where a site is failing to achieve
condition due to pollution, the potential for a new development to add to the
nutrient load is "necessarily limited". Special Areas of
Conservation (SAC) sites are internationally important areas defined by the
National Planning Policy Framework (NPPF) and given special protection under
the European Union's Habitats Directive, which was transposed into UK law by
the Habitats and Conservation of Species Regulations 2010. This was updated
by the Conservation of Habitats and Species (Amendment)(EU Exit) Regulations
2019. As such, Natural England's view is that any development proposal that
adds nutrients into the catchment of internationally important sites, such as
the Somerset Levels and Moors, is likely to have a significant effect.
Proposed developments likely to affect European Sites should be subject to
Habitats Regulations Assessment to assess the Likely Significant Affect on
the SAC. Applications within the catchment that will have a Likely Effect and
will require an Appropriate Assessment (i.e. the nutrient calculator) to
assess the implications of the proposal on the designated sites.
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This
tool is designed to quantify the nutrient loading of an area of land subject
to a change of land use and population, in order to identify is proposed
developments will be 'nutrient neutral'. Where the proposed development will
generate additional nutrients into the system, solutions in how to offset the
excess nutrients and achieve neutrality are presented.
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This tool is only
necessary for proposed developments that have the potential to increase
nutrient loading to rivers that flow into the Somerset Levels and Moors.
Where a site drains to a Water
Recycling Centre (WRC) outside of the catchment then no likely significant
effects can be determined. However, SuDS should still be considered.
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When using the
findings of this tool for a nutrient neutrality assessment, users should
either print the pages as a pdf or screenshot each page, and present this as
evidence of the nutrient budget calculations.
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The methodology
employed within this tool was, in part, guided by Natural England's advice on
nutrient neutrality in relation to the Stodmarsh designated sites (published
in November 2020) and the Natural England provided calculator (published
March 2022).
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This
tool consists of eight main worksheets:
Stage 1 - Identifies the additional nutrients as a result of changes in the
population
Stage 2 - Calculates the nutrient load from current land use
Stage 3 - Calculates the nutrient load from future land uses
Stage 4 - Calculates the total change in nutrient loading as a result of
the proposed development
Mitigation - current -Offers guidance on potential solutions to achieve
nutrient neutrality under current wastewater permit limits
Mitigation - post 2025 - Offers guidance on potential solutions to achieve
nutrient neutrality under AMP7 wastewater permit limits
Mitigation - post 2030 - Offers guidance on potential solutions to achieve
nutrient neutrality under AMP8 wastewater permit limits
Mitigation land use comparison - Calculates the difference in mitigation
solutions between current wastewater permit limits and post-2030 permit
limits
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This nutrient
budget calculator is designed to allow the user to:
- Calculate the nutrient budget for a proposed development, and if, in its
current form, the proposed development is nutrient neutral; and
- Assess the various mitigation options if the proposed development is not
nutrient neutral.
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The tool has been designed so that the user is
able to update the data and methods in light of any new research or
understanding
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The information
supplied in this tool is for guidance purposes only and is not intended to
provide an exact budget calculation due to the limitations and assumptions of
the model. The user is responsible for ensuring the accuracy and completeness
of all data entered, be it manually or automatically, and used by this tool.
The user is also responsible for any commercial decisions taken on any of the
outputs of this tool.
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Royal HaskoningDHV
will not be liable for any of the following arising from the use of this tool
(including from any negligence on the part of Royal HaskoningDHV):
(i) loss of anticipated profits or expected future business;
(ii) damage to reputation or goodwill;
(iii) damages, costs or expenses payable by the user to any third
party;
(iv) loss of any order or contract; or
(v) indirect or consequential loss of any kind.
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This nutrient budget calculator has been developed
by Royal HaskoningDHV on behalf of Somerset Council.
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Phosphorus budget calculator, v2.1 (Released
February 2023)
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The Tool uses the following colour coding to
indicate the functionality to the user. These colours are:
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The user needs to input a value here
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This contains fixed or calculated values and the
user does not need to input a value
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Stage 1
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This stage
calculates the change in nutrient loading as a result of changes in the
population of a site.
Step 1: The user should input the additional number of units that are
proposed by the development. This is then multiplied by the occupancy rate
per dwelling.
Step 2: This automatically calculates the wastewater volume for the
development. British flows and loads can be used for calculating bespoke wastewater volumes.
Step 3: The user has the option to select whether sewage from the proposed
development will be handled by water recycling centres or by Onsite treatment
plants. The user must select one or the other, both options cannot be used.
Step 3a: If the proposed development is to use WRC, then the user should
select 'Yes' from the drop down box. Following this, the user should select
the WRC that the development will connect to. This will select the discharge
concentration from the chosen WRC.
Step 3b: If the proposed development is to use Onsite treatment plants,
then the user should select 'Yes' from the drop down box. Following this, the
user should input the final effluent quality of the onsite treatment plant.
If the efficiency is unknown then the user should input a precautionary
default values. Higher removal rates can be achieved through Package
Treatment Plants (PTPs) but these will typically require additional phosphate
reduction such as chemical dosing that standard PTPs may not include.
Step 4: This automatically calculates the Total Phosphorus (TP) and Total
Nitrogen (TN) loading from wastewater
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Stage 2
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This stage calculates the nutrient load from the current
land use.
Step 1: The user should select the appropriate catchment, drainage type,
rainfall band and NVZ.
Step 2: The user should input the area (hectares) of the current land uses
that make up the total area of the development site. A GIS viewer can be used
to identify the land uses on a coarse scale (https://gridreferencefinder.com/). However, if more detail is known about the site land uses
then this should be manually inputted by the user. The % removal from any
existing SuDS can be inputted. Where the existing land use falls in the 'low
density residential urban' category, a standard removal of 85% should be
applied.
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Stage 3
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This stage
calculates the nutrient load from the future land use.
Step 1: The user should input the proposed land uses that make up the total
area of the development site. Any pre-determined on-site mitigation should
also be inputted here.
Bespoke banking coefficients should be inputted for constructed wetland
that can be evidenced
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Stage 4
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This stage
provides a summary of the nutrient loads calculated in stages 1-3 and
presents the nutrient budget for the proposed development.
A 20% precautionary buffer is included to account for uncertainties in the
runoff coefficients used.
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Mitigation - Current
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This stage
calculates the area and land uses of the mitigation site required for the
proposed development to be nutrient neutral, under current WRC permit
limits.
Step 1: The nutrient budget to be mitigated will be automatically shown
Step 2: The user should either select 'Yes' for on-site mitigation (step
2a) or 'Yes' off-site mitigation (step 2b). For on-site mitigation, the user
should select the land use which the mitigation land will be replacing. Where
the exact land use type is unknown, an average value can be used. For off-site mitigation, the catchment,
soil drainage type, rainfall band and NVZ should be selected for the
mitigation land and the most appropriate land use(s) selected.
Step 3: This will automatically show the area required for mitigation to
achieve neutrality for each land use type.
Step 4: The user has the option to select the amount of nutrient load to be
offset by the various land uses, which will then calculate the relevant area
of land (Hectares) that needs to be changed.
Step 5: The user has the option to input the required area of land
(hectares) to be mitigated until the project is nutrient neutral, which will
then calculate the equivalent nutrient load for each land use.
The banking coefficients for wetlands uses a value for guidance purposes
only. A site bespoke site-specific value will need to be calculated.
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Mitigation - Post 2025
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This stage
calculates the area and land uses of the mitigation site required for the
proposed development to be nutrient neutral, under post-2025 WRC permit
limits. This only applies to TP. The steps are the same as 'Mitigation -
current'.
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Mitigation - post 2030
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This stage
calculates the area and land uses of the mitigation site required for the
proposed development to be nutrient neutral, under post-2025 WRC permit
limits. This stage is for guidance purposes only. The steps are the same as
'Mitigation - current'.
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Mitigation comparison
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This stage
provides a summary in the differences in mitigation land use area between the
current WRC permit limits and the post-2030 WRC permit limits.
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The land uses presented in this tool followed the
CORINE 2018 land use data. Definitions of key land uses are presented below:
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Land Use
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Description
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Residential urban
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Areas
of houses and associated infrastructure. This is inclusive of roads,
driveways, grass verges and gardens.
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Low density
residential urban
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Rural communities are classed under low density
residential land. Low density residential developments will typically have
less than 25 units per hectare.
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Commercial /
industrial
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Land used for commercial establishments (the
primary purpose of buying, selling or trading of merchandise or services
including, without limitation, shopping malls, office complexes, restaurants,
hotels, motels, grocery stores, automobile service stations, petroleum
distribution operations, dry cleaning operations, municipal yards,
warehouses, law courts, museums, churches, golf courses, government offices,
air and sea terminals, bus and railway stations, and storage associated with
these uses) , manufacturing plants, public utilities, mining, distribution of
goods or services, administration of business activities, research and
development facilities, warehousing, shipping, transporting, remanufacturing,
stockpiling of raw materials, storage, repair and maintenance of commercial
machinery or equipment, and waste management.
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Urban open
space
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Area of land in urban areas used for various
purposes, e.g. leisure and recreation - may include open land, e.g. sports
fields, playgrounds, public squares or built facilities such as sports
centres.
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Allotment and
City farms
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Wholly
or mainly cultivated for the production of vegetable or fruit crops for
consumption by the tenant or local community. In some cases the land will
also be used for ornamental plants and the keeping of hens or bees.
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Dairy
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Holdings on which dairy
cows account for more than two thirds of their total standard output.
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Cereals
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Agricultural
areas on which cereals, combinable crops and set aside are farmed.
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Horticulture
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Holdings
on which fruit (including vineyards), hardy nursery stock, glasshouse flowers
and vegetables, market garden scale vegetables, outdoor blubs and flowers and
mushrooms account for more than two thirds of their total standard output.
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Pig Farming
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Holdings on which pigs
account for more than two thirds of their total standard output.
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LFA
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Holdings
on which cattle, sheep and other grazing livestock account for more than two
thirds of their total standard output except holdings classified as diary. A
holding is classified as LFA if more than 50% of its total area is in the
Less Favoured Area (LFA).
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Lowland grazing
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Holdings
on which cattle, sheep and other grazing livestock account for more than two
thirds of their total standard output except holdings classified as diary. A
holding is classified as lowland if less than 50% of its total area is in the
Less Favoured Area (LFA). A paddock is classified as a small enclosures used
for grazing horses.
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Mixed
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Holdings
for which none of the other categories account for more than two thirds of
total standard output.
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Poultry farming
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Holdings on which poultry
account for more than two thirds of their total standard output.
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General Arable
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Agricultural
areas on which arable crops (including field scale vegetables) are farmed.
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Greenspace
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Natural
and semi-natural outdoor spaces provided for recreational use where
fertilisers will not be applied and dog waste is managed, e.g. semi-natural
parks. This does not include green infrastructure within the built urban
environment as this is included in the urban categories.
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Woodland
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Tree-covered
areas which either arose naturally or as a result of plantations. This
includes conifer woodland, mixed woodlands and broad-leaved woodlands etc.
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shrub /
heathland / bracken / bog
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Land
that contains extensive areas of either shrubs, heath or bracken. A bog
refers to land that is a wetland area of muddy ground that can accumulate
peat.
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Water
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Areas of surface water, including rivers, ponds
and lakes.
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Meadow / semi
natural grassland
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A
meadow is a field habitat vegetated by grass and other non-woody plant that
has an open character and is not grazed by livestock
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Wetland
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Land
use specific to constructed wetland only and does not include ponds or SuDS.
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WRCs with a
phosphorus permit are assumed to discharge at 90% of the permit. Measured
data was used to derive the posphorus dicharge for unpermitted WRCs. 2025 and 2030 permit limits are
incorporated into the calculator. Note that Broadway WRC & Ilminster were
upgraded by December 2023, prior to 2025 deadline.
Please note that the calculator has adopted the stretch
targets agreed for the WRCs in the catchment, as
published by Wessex Water.
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The drainage
characteristics of soil has a control over the dominant flow pathways for
pollutant losses and as such controls the loading of Phosphorus into surface
water bodies. Therefore the runoff coefficients from various land uses are
different in freely draining soil compared to impermeable soil. For
impermeable soil under Arable land use, it is assumed that man made drainage
systems would be in place, whereas rough grazing and woodland areas would not
be drained. For free-draining soil, the majority of the flow would be to
groundwater, and it is assumed that drainage would not be required.
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b) Zoom into the
development site on the map
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c) Once the area
has been located, click on the map where the development is located to find
out the ID number and name of the soil type.
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d) Make note of
this and determine the drainage type using the below table
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The following
table is used to identify the dominant drainage type of the proposed
development from the soil type identified above. The drainage type should
then inform Stage 2 of the calculator
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Free draining
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Impermeable
- drained for arable
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Impermeable - drained
for arable & grassland
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Colour
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ID
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Name
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Colour
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ID
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Name
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colour
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ID
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Name
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3
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Shallow lime-rich soils over chalk or limestone
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1
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Saltmarsh soils
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17
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Slowly permeable seasonally wet
acid loamy and clayey soils
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4
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Sand dune soils
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2
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Shallow very acid peaty soils over rock
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18
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Slowly permeable seasonally wet
slightly acid but base-rich loamy and clayey soils
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5
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Freely draining lime-rich loamy soils
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8
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Slightly acid loamy and clayey soils with impeded drainage
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19
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Slowly permeable wet very acid
upland soils with a peaty surface
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6
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Freely draining slightly acid loamy soils
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9
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Lime-rich loamy and clayey soils with impeded drainage
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7
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Freely draining slightly acid but base-rich soils
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15
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Naturally wet
very acid sandy and loamy soils
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10
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Freely draining slightly acid sandy soils
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16
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Very acid loamy upland soils with a wet peaty surface
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11
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Freely draining sandy Breckland soils
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20
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Loamy and clayey floodplain soils with naturally high
groundwater
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12
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Freely draining floodplain soils
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21
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Loamy and clayey soils of coastal flats with naturally high
groundwater
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13
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Freely draining acid loamy soils over rock
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22
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Loamy soils with naturally high groundwater
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14
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Freely draining very acid sandy and loamy soils
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23
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Loamy and sandy soils with naturally high groundwater and a
peaty surface
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24
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Restored soils mostly from quarry and opencast spoil
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25
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Blanket bog peat soils
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26
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Raised bog peat soils
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27
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Fen peat soils
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b) This will give a
high-level view of operational catchments Use the zoom feature to find the
exact location of the development.
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c) Click on the
light blue area on the map in which the development is located. This will
inform the user of the operational catchment name
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d) Make note of the name of the Operational
Catchment and select it from the dropdown list in the relevant cell.
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b) Enter the location of the development site in
the search bar.
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c) Once the area
has been located, click on the map where the development is located to find
out if is within an NVZ.
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d) Make note of this and select this in the
dropdown list.
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HaskoningDHV UK
Ltd., a company of Royal
HaskoningDHV
1 Emperor Way, Exeter Business Park
Exeter, Devon, EX1 3QS
Registered in England 1336844
W: www.royalhaskoningdhv.com
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