Final River Fushoge Catchment Report Rev 1

School of Engineering
Department of the Built Environment
BEng (Hons) in Civil Engineering, 2014
River Fushoge Catchment Report
Seán Bolton
Date Submitted: 02/05/2014 Word Count: 5,023

Table of Contents
1.0 Introduction................................................................................................................................1
1.1 General Overview of Catchment...................................................................................................1
2.0 Brief Catchment Description......................................................................................................3
3.0 Precipitation & Recharge Analysis.............................................................................................6
3.1 Calculations...................................................................................................................................6
3.2 Discussion on Calculations............................................................................................................6
3.3 Recharge .......................................................................................................................................7
3.3 HydroTools Output........................................................................................................................8
4.0 Estimating Flood Flow................................................................................................................9
4.1 Calculations...................................................................................................................................9
4.2 Discussion......................................................................................................................................9
5.0 Applying HEC-RAS Software to Estimate Flood Levels............................................................10
5.1 Introduction ................................................................................................................................10
5.2 Observations Made on Site Investigation...................................................................................11
5.3 Conclusions Drawn From Site Visit .............................................................................................14
5.4 Data From Field Study.................................................................................................................15
5.5 Conclusions Drawn From HEC – RAS Output ..............................................................................18
5.6 Comments on Process.................................................................................................................18
6.0 Surface Water Quality..............................................................................................................19
7.0 Groundwater Investigation......................................................................................................21
7.1 Bedrock Aquifer Designation ......................................................................................................21
7.2 Gravel Aquifer Designation.........................................................................................................22
7.3 Catchment Vulnerability .............................................................................................................23
7.4 Proposed Well For Domestic Dwelling........................................................................................24
7.41 Discussion..............................................................................................................................26
8.0 Assimilative Capacity ...............................................................................................................26
8.1 Septic Tank Site Investigation .....................................................................................................27
8.2 Site Classification Form...............................................................................................................28

Table of Figures
Figure 1-1- Catchment Map....................................................................................................................1
Figure 1-2 - River Segment Map .............................................................................................................2
Figure 3-1 - Recharge Map......................................................................................................................7
Figure 3-2 - Flow Duration Curve............................................................................................................8
Figure 5-1 - Upstream View of River Section........................................................................................11
Figure 5-2 - Downstream View of River Section ...................................................................................11
Figure 5-3 - Waterlogging of Agricultural Land Adjacent to River Section ...........................................12
Figure 5-4 - View of River From Under the Bridge at the Cross-Section Location................................12
Figure 5-5 - Vegetation Observed Along River Bank.............................................................................13
Figure 5-6 - View of Steeply Sloped Catchment Area...........................................................................13
Figure 5-7 - Vegetation in Stream.........................................................................................................14
Figure 5-8 - Resedential Area Adjacent to River Stream ......................................................................14
Figure 5-9 - Upstream Cross-Section ....................................................................................................16
Figure 5-10 - Downstream Cross-Section .............................................................................................16
Figure 5-11 - 3D River Section...............................................................................................................17
Figure 5-12 - Longitudinal Section ........................................................................................................17
Figure 5-13 - Rating Curve.....................................................................................................................17
Figure 6-1 - River Water Quality Sections Along Fushoge ....................................................................19
Figure 7-1 - Bedrock Aquifer Map.........................................................................................................21
Figure 7-2 - Gravel Aquifer Map ...........................................................................................................22
Figure 7-3 - Catchment Vulnerability Map............................................................................................23
Figure 7-4 - Location of Proposed Well.................................................................................................24
Figure 7-5 - Location of Proposed Site as Viewed From the River........................................................24
Figure 7-6 - Image of Proposed Site in Relation to Existing Well..........................................................25
Figure 7-7 - Existing Well Pumping Results...........................................................................................25
Table of Tables
Table 3-1 – Actual Recharge Calculation.................................................................................................6
Table 4-1 - Soil Factor Calculation...........................................................................................................9
Table 4-2 - Q100 Calculation...................................................................................................................9
Table 5-1 - HEC-RAS Input Data ............................................................................................................15
Table 5-2 - Channel Geometry..............................................................................................................15
Table 8-1 - Assimilative Capacity Calculation Input Data......................................................................26
Table 8-2 - Assimilative Capacity Calculation........................................................................................27

Seán Bolton – River Fushoge Catchment Report – C00128310
Jer Keohane – Environmental Engineering – Civ. Eng. (Y5) – I.T. Carlow Page 1
River Fushoge Catchment Report
1.0 Introduction
In this report the River Fushoge and the geological conditions of its catchment area located in Co.
Laois will be investigated. The stream investigation will be undertaken at a downstream section of
the river, near to a proposed site requiring a water source and wastewater treatment system.
How the river conditions influence and indeed are influenced by the surrounding catchment area
will also be investigated. This investigation will be based on information as provided by the
Environmental Protection Agency and Ordinance Survey Ireland.
1.1 General Overview of Catchment
The catchment is located in the south-eastern corner of Co. Laois, near the border with Co. Carlow.
The catchment area encompasses a generally steeply sloped region to the west, with a large portion
of flow within the river fed from the runoff and throughflow of water from this region.
Figure 1-1- Catchment Map

The illustration on the previous page clearly outlines the catchment area whilst highlighting the
furthest downstream section which will be examined within this report. It must be noted that the
river continues for several kilometres downstream before it enters the River Barrow.
As such, the overall catchment area is significantly larger than what will be examined for the purpose
of this report. This section of the catchment was chosen due to its close proximity to the site on
which a wastewater system was proposed to be constructed. This would allow for the importance of
this river be determined as a measure of water flow volume. The presence of a bridge also meant
that visual inspections could be easily made when required.
Figure 1-2 - River Segment Map

2.0 Brief Catchment Description
The following is a brief summary of the findings of the report and those produced by the hydrotools
resource. A more detailed description of each section may be found within the report, if such
detailed description is necessary.
Catchment Area: 32.7 m2
.
Main Stream Length: 58.4km
Average Slope of Catchment: 7.2%. This steep ground will generate faster run-offs run-off meaning
that times of concentration will be faster and flood peaks higher. This explains the rapid increase in
flow within the river after heavy periods of rainfall as discussed further within this report.
Catchment Orientation: Northwest –Southeast Orientation. The prevailing wind is from south-west.
Shape of Catchment: Long, relatively straight main stream. Smaller streams join from up-gradient
reaches of catchment. Shape indicates long time for all parts of catchment to contribute to river
flow.
Stream Frequency: approximately 35 individual streams upstream of monitoring point. Many
reasonably large streams within catchment area, stream density is therefore considerable. There is a
total of 1.786km of stream per m2
of catchment area.
Lake & Reservoir Area: No considerable lake area, with the exception of a relatively small reservoir
area which previously served as a storage pond for the Carlow Town water treatment system.
FARL Index: 1.0. This rating indicates little or no flood attenuation by reservoirs & lakes, therefore
indicating that water runoff enters the stream exceptionally quickly.
Land Use: Land use is primarily rural. There are some regions of forestry, although recent local
deforestation of farmed trees has considerably reduced this area.
Climatic Factors: Typical of region. There may be increased evaporation due to reduced drainage
into the water table as a result of the poorly drained soil of the region.
Precipitation: Mainly rain. Some sleet or snow in winter months, this is highly variable annually.

Figure 2-1 - Catchment Descriptors
The soil information in the table shows that in general the soil of the catchment is poorly drained.
From this it was assumed that potential problems may exist with regard to the installation of a
domestic waste water treatment system.
There are also significant regions where soil is well drained, however these zones are in the minority.
It can also be seen that there is a small amount of peat material within the region, meaning slope
stability and soil bearing capacity may be an issue in certain regions.

Figure 2-2 - Subsoil Permeability
It can be seen that there are large areas of this catchment where there is no subsoil present and
bare rock is exposed at the surface. This is consistent with what would be expected in an upland
region. This exposed rock is possibly what causes rapid flow within the river after periods of heavy
rainfall as water runs directly off the rock and into the stream. Further reporting on the implications
this has on groundwater vulnerability is dealt with later in this report.
Of the subsoil which is present much of this can be seen to be of low to moderate permeability. This
confirms the difficulties anticipated with regard to the proposed wastewater treatment site. From
this it can be concluded that should a septic tank system be installed within the subsoil of this region
strict guidelines would have to be followed to avoid adversely influencing the surrounding
environment. This again is dealt with further in a later section of the report.
The majority of the catchment lies in a region designated as being a poor aquifer. Whilst a small
percentage of the catchment is situated in regionally or locally important aquifer regions, the vast
majority of this catchment area is unsuitable for large scale groundwater abstraction. Locally
productive zones must therefore be located for any proposed domestic water source.

3.0 Precipitation & Recharge Analysis
3.1 Calculations
Average Annual Rainfall 840 mm
Estimated P.E. 459 mm
Estimated A.E 436 mm
Rainfall Losses 349 mm
Estimated Actual Recharge 87 mm
Table 3-1 – Actual Recharge Calculation
Catchment Area : 32.7 km2
32700000 m2
Rainfall Losses : 0.349 m2
Estimated Flow : 0.361 m3
/s
Actual 50%ile Flow: 0.375 m3
/s
Table 3-2 - 50%ile Flow Calculation
3.2 Discussion on Calculations
From the calculations it can be seen that the calculated flow was estimated to be relatively close to
that which was recorded and published on the EPA Hydrometric Data System; HydroTools. These
results are illustrated on the following page. This proves that the method of calculation used is
accurate in predicted actual flows along the river, within the catchment in question.
The soil in this catchment is said to be largely poorly-drained, meaning that water which falls on the
catchment would be expected to be retained in the soil, attenuating peak discharge in the river. The
catchment is also, however, of significantly steep gradient, meaning that overland flow would lead
to rapid peak flows within the river.
Should the poorly drained soil become saturated during periods of heavy rainfall it could be
expected that peak flows after heavy rainfall would be relatively flashy. This is true as the voids in
the saturated soil would already be full of water, resulting in the excess rainwater running directly
into the river as a consequence.
This assumption can be confirmed by observation of the river after periods of heavy rain, with flow
having been observed to increase rapidly during the hours after such periods.

3.3 Recharge
Figure 3-1 - Recharge Map
The map shown above illustrates the recharge data for the River Fushoge catchment area under
investigation. The catchment area is largely confined to the area of relatively poor recharge to the
east of Carlow Town, with recharge values for the catchment area rarely exceeding 100mm. This
coincides with the recharge value of 87mm which was estimated earlier in this report. This verifies
the calculation method used, whilst further reinstating the consensus that the River Fushoge
catchment area is generally poorly drained and rather boggy in places.
This poor drained soil is reflected in the recharge values, with a relatively small quantity of water
entering the groundwater table through seepage into the soil. This means that overland runoff
within this region is likely to be reasonably large, given the steeply sloped nature of this poor
draining soil.
It may therefore be concluded that the flashy nature of flow within the River Fushoge as outlined
previously is due to the poor recharge highlighted within this section of the report. This means that
overland runoff may be disproportional to groundwater recharge, increasing the risk of flooding
within the river during periods of heavy prolonged rainfall.

This poor recharge may also mean that this region is not suitable if a ground water source was to be
required, as groundwater levels may be slow to recharge should they be depleted as a result of
pumping for water supply provision.
Another consequence of this poor recharge may be that this region is possibly largely unsuitable for
the installation of basic domestic waste treatment systems. Poor recharge may result in poor
percolation of effluent and could result in ponding of this effluent at the surface should a basic
treatment system be installed. Further investigation may be required to determine whether this is,
in fact, the case.
3.3 HydroTools Output
Figure 3-2 - Flow Duration Curve
From The information provided above it can be seen that the river has a 95%ile flow of
approximately 0.05 m3
/s, with this low flow is exceeded 95% of the time. It can be seen from the
information shown above that this is a relatively small river, with flow rarely exceeding 1.4 m3
/s.
The results produced confirm what was estimated by the calculations shown previously, affirming
the validity of the calculation approach used.

4.0 Estimating Flood Flow
4.1 Calculations
Soil Type Area (km2
) Soil % Soil Factor Soil Factor Contribution
2 10.114 30.93 0.3 0.0928
4 7.243 22.15 0.45 0.0997
5 15.343 46.92 0.5 0.235
Table 4-1 - Soil Factor Calculation
4.2 Discussion
The tables above illustrate the
calculations carried out in order
to obtain the estimated
maximum flow that would be
expected in the river annually,
with a return period of 100 years
(Q100). These figures are taken to
represent those expected within
the River Fushoge Catchment
area, located as shown.
Total Area = 32.7 km2
Total Soil Factor= 0.427
SAAR= 830 mm/yr
Qbar= 10.844 m3
/s
Multiply by factor of 1.96
Q100= 21.2543 m3
/s
Add 20% for climate change
New Q100 = 25.505 m3
/s
Table 4-2 - Q100 Calculation
Figure 4-1 - Catchment Location Map

The proportion of soil type within the
catchment was calculated by superimposing
an outline of the catchment area onto a soil
map of Ireland, as illustrated. By calculating
the area of each soil type which is present
within the Fushoge Catchment area it was
possible to define the percentage of each by
dividing the individual soil areas by the
overall area of the catchment.
From this it was possible to calculate the contribution factor of each soil type by multiplying the
percentage quantity of the soil type by a predefined soil factor. Each individual factor was then
added to give a total soil factor for the catchment area. By obtaining the Standard Average Annual
Rainfall (SAAR) value from hydrotools Qbar for the catchment could be calculated using a standard
equation. The annual maximum d=flow was then calculated by multiplying Qbar by a growth factor of
1.96 to give Q100.
This figure was then increased by 20% to allow for rainfall intensity increases predicted as a result of
future climate change, to give a design Q100 value of 25.505 m3
/s for the River Fushoge, based on the
catchment parameters. This value could be used as the basis for making general long-term design
assumptions should they be required.
5.0 Applying HEC-RAS Software to Estimate Flood Levels
5.1 Introduction
A site visit was undertaken on 02/01/2014 to establish the physical properties of a section of the
River Fushoge, this section measuring approximately 50m in length. This section was chosen due to
its close proximity to a relatively densely populated residential area, which would be especially
susceptible to flooding, should this found to be a potential problem.
For health and safety reasons observations were made from a bridge which crosses the river
approximately mid-way along the section under examination. This was done due to the high rate of
flow within the river channel as a consequence of a prolonged period of stormy weather in the days
and weeks prior to the date on which the inspection was undertaken.
These observations were supported by minor supplementary observations made from a position on
the river bank immediately adjacent to the bridge mentioned above.
Figure 4-2 - Catchment Outline Map

5.2 Observations Made on Site Investigation
The following images illustrate the conditions on the river section examined on the day of the site
investigation.
Figure 5-1 - Upstream View of River Section
Figure 5-2 - Downstream View of River Section

Figure 5-3 - Waterlogging of Agricultural Land Adjacent to River Section
Figure 5-4 - View of River From Under the Bridge at the Cross-Section Location

Figure 5-5 - Vegetation Observed Along River Bank
Figure 5-6 - View of Steeply Sloped Catchment Area

5.3 Conclusions Drawn From Site Visit
The site visit allowed for a rough estimate of river cross section parameters to be estimated. This
includes channel dimensions along with the roughness coefficient which was to be inputted into the
HEC – RAS software package.
The roughness factor of the river was assumed to be relatively high, due to the presence of large
amounts of weeds and brush along the river banks, and also due to the presence of a fallen tree
within the downstream river section. This tree extended across the stream to approximately ¾ of the
total stream width. This is reflected in the roughness value which was inputted into HEC – RAS, as
illustrated in the next section of the report.
Figure 5-7 - Vegetation in Stream
Figure 5-8 - Residential Area Adjacent to River Stream

The width of the stream was estimated by roughly measuring out the length of bridge which crossed
the river stream, with a small allowance made to take account for the curvature of the bridge which
would increase the measured distance. This was done as safe access to the river was not possible on
the day of the site visit, as outlined previously.
This site was chosen due to the proximity of the residential area, making this area especially
susceptible to damage as a result of flooding, meaning flood avoidance is of increased priority. This
section of the river is also immediately upstream of a noted decrease in water quality, as outlined in
an earlier section of this report.
5.4 Data From Field Study
The following data was used in the HEC – RAS programme for calculating the flood risk of the river
section.
Parameter Value
Section Length 50m
Upstream n Value (LOB) 0.07
Upstream n Value (Channel) 0.045
Upstream n Value (ROB) 0.05
Downstream n Value (LOB) 0.07
Downstream n Value (Channel) 0.1
Downstream n Value (ROB) 0.07
Main Channel Bank Stations (LB) 3
Main Channel Bank Stations (RB) 11
Contraction Coefficient (Steady Flow) 0.1
Expansion Coefficient (Steady Flow) 0.3
Table 5-1 - HEC-RAS Input Data
The estimated channel dimensions which were used are illustrated in the table below.
Cross Section Coordinates
Station Elevation
0 100
3 98
4 96
10 96
11 98
14 100
Table 5-2 - Channel Geometry
It was assumed, from observation that the channel was approximately of the same dimensions for
the entire 50m stretch of the river under inspection. The resulting cross-sections are illustrated
below, which may be considered to represent a reasonable approximation of the river as observed.

Figure 5-9 - Upstream Cross-Section
Figure 5-10 - Downstream Cross-Section

Figure 5-11 - 3D River Section
Figure 5-12 - Longitudinal Section
Figure 5-13 - Rating Curve

5.5 Conclusions Drawn From HEC – RAS Output
The results from the HEC – RAS program indicate that in the 1 in 100 storm scenario the river level
will exceed its channel as defined on the site visit. The river will not flood over into the surrounding
area, however, due to the height of the steeply sloping river banks on either side of the river
channel. It can therefore be concluded that the HEC – RAS program suggests that the residential
area located in the river section is not in danger of flood damage.
This assumption is supported by local knowledge, with there being no record of this river causing
flooding in the locality. Some flooding has been known to occur as a result of waterlogging of the
nearby poorly drained agricultural land, such as that illustrated in a previous section of this report.
The longitudinal section illustrates the gradual channel slope, whilst the computed rating curve
shows a linear relationship between stage and flow in this section of river.
5.6 Comments on Process
He river dimensions chosen appear excessive on second inspection. A channel width of 6m may
have been an overestimation, as the images appear to suggest. If this river section was to be tested
in practice appropriate surveying equipment would be necessary to ensure accurate measurements
are recorded.
For the purely academic nature of this exercise, however, these figures were useful in allowing for
the use of the HEC – RAS program to estimate flood risk. As the results indicated the surrounding
land was not at risk of flooding damage, a fact supported by local knowledge, it may be said that the
results do still provide a certain level of accuracy.
The roughness coefficient was also noted as being a particularly subjective area, with this being
largely down to individual interpretation. A small difference in this value can have dramatic
consequences on results, meaning that great care should be taken to ensure accuracy in the
assumptions of n value made. Adequate site investigation is required to best provide for accuracy in
this vital parameter should the HEC – RAS program be used in future.

6.0 Surface Water Quality
Figure 6-1 - River Water Quality Sections Along Fushoge
Q 4 –Good Status
Q3 – 4 – Moderate Status
Q2 – 3, Q3 – Poor Status
In Fig. 6-1 the River Fushoge flows from north to south, starting approximately at the station which
shows good water quality status, to the left of centre at the background of the image. The river flows
to the station in which water of poor status was recorded, in the right foreground of the image,
where it joins the River Barrow.
It can be seen that in the upstream portion of the river water quality is generally of good status, with
this gradually deteriorating downstream within the river. It can therefore be concluded that as the
stream flows through the catchment area, a degree of pollutants are being discharged into the river.
It is noted that the recording station which indicates water of moderate status is located
immediately downstream of a relatively densely populated residential area, with a hygiene systems
production plant located nearby. This is also the point at which the catchment study outlined earlier
in the report is concentrated.
This change in water quality may indicate that there is pollutant being discharged into the river
within this section of the river stream. It may be worthwhile to carry out an investigation into
possible sources of contamination within this section of the catchment.

Water quality is again recorded as being of good status at a station located further downstream of
this point. This further suggests the likelihood of some form of point source pollution near the
upstream recording station.
The final station on the river, located immediately prior to the Fushoge joining the River Barrow
indicates water of poor status. As this is located immediately downstream of a station where water
is of good status, further pollution of the river at this point is possible. It may also be possible that a
backwater effect from the River Barrow, where water quality is lower immediately outside Carlow
Town, occurs at this point. Due to the close proximity to the confluence with the River Barrow, it is
possible that this data indicates a transitional section.
A slight concern if the above theory is to be true is the fact that water quality in the River Barrow
immediately upstream of the confluence is recorded as being of moderate rather than poor status.
This sudden quality drop may indicate that pollution is in fact the cause of the deterioration in water
quality on the river. This is also a region of relatively dense population along the river Fushoge, a
possible source of pollution.
Although further investigation is required for confirmation, it may be concluded from this study that
within regions of relatively dense residential and industrial activity pollution of the River Fushoge is a
potential source of water quality deterioration. If this is found to be the case mitigating measure
should be taken to reduce or eliminate direct pollution of the river stream.

7.0 Groundwater Investigation
7.1 Bedrock Aquifer Designation
Figure 7-1 - Bedrock Aquifer Map
The map shown above illustrates the bedrock aquifer designation of the section of catchment under
investigation. This map illustrates what was described earlier in the report, with it being clear from
the map that a large section of the catchment area is located in an aquifer designated as a poor
aquifer.
This map also illustrates the section of the catchment which lies within a zone designated as being
regionally and locally important. These can be seen to be located to the eastern and western most
extremes of the catchment area. Should a large scale groundwater water scheme be required it
would therefore be advisable to develop within these regions.

7.2 Gravel Aquifer Designation.
Figure 7-2 - Gravel Aquifer Map
The map above illustrates that the catchment area is not generally located on a region of significant
gravel deposits. It can be seen that there is a large region of significant gravel aquifer to the east of
the site, running through Carlow town.
This zone does not generally protrude into the River Fushoge catchment, with only small regions to
the south-eastern corner of the catchment being situated in close proximity to this geological
formation.

7.3 Catchment Vulnerability
Figure 7-3 - Catchment Vulnerability Map
The map shown above illustrates the vulnerability designation of the section of catchment under
investigation. From this map it can be concluded that much of the catchment area, especially regions
to the north, have been designated as being of high or extreme vulnerability. This means that much
of the catchment area is susceptible to groundwater contamination due to the thin layer of soil over
bedrock in these regions. This high vulnerability is due largely to the shallow regional overburden
depth.
A region to the south of the catchment can be seen to have been designated as being of moderate
to low vulnerability. As these regions are known to be in a more lowland area of the catchment it
can be concluded that the lower vulnerability is due to a thicker layer of soil being present over the
bedrock in this region.
From this information it can be concluded that when developing a septic tank and wastewater
treatment system in the north of the catchment great care must be taken to avoid contamination of
the groundwater table. When such a system is to be installed to the southern extremes of the
catchment area, however, a more standard design scheme can be adopted due to the significantly
lower vulnerability of the groundwater table within this region of the catchment area.

7.4 Proposed Well For Domestic Dwelling
It was decided to investigate the potential of the site chosen for a water treatment system to also
source water for the proposed domestic house to be constructed. This site is located as indicated on
the map shown below.
This site is located approximately 5 km west of Carlow Town, and approximately 1.6km west of the
River Fushoge, in the mid-lower section of the steeply sloped region. A view of the site relative to
the river is shown below. This photo was taken at the river during the flood study investigation.
Figure 7-5 - Location of Proposed Site as Viewed From the River
Figure 7-4 - Location of Proposed Well

This site was selected as it is in close proximity to a well where water production data is known. As
the majority of the catchment area is designated as a poor aquifer, the success of a bored well is
almost equal at any location. Successful water sources are reliant on the presence of locally
productive zones being located.
Figure 7-6 - Image of Proposed Site in Relation to Existing Well
The location of the proposed house site is shown above. Data is known for the existing house to the
north-east of the site, data for this well is shown below. An existing well is also present for the
existing house to the south-east of the site. Data for this well is unavailable.
Figure 7-7 - Existing Well Pumping Results

7.41 Discussion
The proposed water source must be located up-gradient of the proposed wastewater treatment
system. This must be of sufficient distance to ensure no contamination of drinking water occurs. This
site is located in an area dealt with in the Shanragh Water Body Report. This document is included in
the appendices of the report.
The data known from the existing well to the north-east of the proposed site provides an indication
of the aquifer conditions which are probable in the case of the proposed site. This data indicates that
bedrock is extremely close to the surface, approximately 0.6m deep. This is supported by the
vulnerability data, which suggests extreme contamination vulnerability in this region due to the lack
of overburden soil.
Based on the data from the existing well it may be assumed that any groundwater source for this
site will be most likely suitable for domestic use only, with only relatively poor yields being available.
It may be expected to encounter water at approximately 10-13m, based on the known data,
although this data may not necessarily be true for this site, due to the severely sloping topography of
the region. A locally productive zone should be identified prior to drilling to ensure an adequate
supply source is located for the site.
The underlying layers of shale, along with small amounts of coal deposits in the region, may mean
that a filter should be positioned on the water intake of the borehole pump. This may avoid the
presence of solid mineral deposits in the water, which have been reported to cause clogging of
domestic taps in the existing houses within the region.
8.0 Assimilative Capacity
Calculation of assimilative capacity was undertaken using the parameters as outlined within the
table below.
Discharge 70 m3
/day
BOD 10 mg/l
95%ile 0.041 m3
/s
Cmax 4 mg/l
Assume
Cback 2 mg/l
Table 8-1 - Assimilative Capacity Calculation Input Data
Due to the lack of available information it was decided to assume values for effluent discharge, BOD,
Cmax and Cmin with the actual recorded value of 95%ile flow being used. The use of these given values
allowed for an example assimilative capacity calculation to be carried out in accordance with the

Discharge to Surface Waters guidance document published by the Local Authority National Training
Group.
The calculation exercise resulted in the following figures being obtained;
Assimilative Capacity
7.08 kg/day
Effluent Load
0.7 kg/day
% Assimilative Capacity
9.88 %
Mass Balance
2.04 mg/l
Table 8-2 - Assimilative Capacity Calculation
Based on the given parameters it was estimated that the assimilative capacity of the stream at
95%ile flow was approximately equal to 7kg/day. Using the discharge concentration figures as
illustrated, it was determined that an effluent load of 0.7kg/day would be discharged into the
system, an assimilative capacity usage of approximately 10%.
Mass balance was then calculated as being approximately 2mg/l, with this providing a reference
value which can be compared directly with the water quality standard (EQS) to determine whether
the discharge will cause an exceedance of the EQS value.
8.1 Septic Tank Site Investigation
Having completed the catchment assessment it was decided to investigate a site towards the west of
the catchment area, in the lowlands of the steeply sloping area of the catchment. This site is
mentioned earlier in the report, and is located on the satellite images provided. The following site
classification form describes the suitability of the site for use in private water treatment in the form
of a septic tank. This site classification form is shown on the following pages.

8.2 Site Classification Form

The data from the following maps was used for completion of the site classification form.

Final River Fushoge Catchment Report Rev 1

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