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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