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Hydrological Assessment of the Bellair Development

Report

Version – 4

4 October 2016

Triplo4 Sustainable Solutions

GCS Project Number: 16-0867

Client Reference: GCS Bellair Hydrology

Triplo4 Sustainable Solutions Bellair Development Housing Estate

16-0867 4 October 2016 Page ii

HYDROLOGICAL ASSESSMENT OF THE BELLAIR DEVELOPMENT

Report Version – 4

4 October 2016

Triplo4 Sustainable Solutions

16-0867

DOCUMENT ISSUE STATUS

Report Issue Version - 4

GCS Reference Number GCS Ref - PN 16-0867

Client Reference GCS Bellair Hydrology

Title Hydrological Assessment of the Bellair Development

Name Signature Date

Author Craig Orchard

October 2016

Document Reviewer Robert Verger

October 2016

Unit Manager Karen King

October 2016

Director Pieter Labuschagne

October 2016

LEGAL NOTICE This report or any proportion thereof and any associated documentation remain the property of GCS until the mandator effects payment of all fees and disbursements due to GCS in terms of the GCS Conditions of Contract and Project Acceptance Form. Notwithstanding the aforesaid, any reproduction, duplication, copying, adaptation, editing, change, disclosure, publication, distribution, incorporation, modification, lending, transfer, sending, delivering, serving or broadcasting must be authorised in writing by GCS.


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LIST OF ACRONYMS

Acronym Description

DWS Department of Water and Sanitation

GCS GCS Water and Environment (Pty) Ltd

IWULA Integrated Water Use License Application

mamsl Metres Above Mean Sea Level

m3/month Water consumption – cubic metres per month

MAE Mean Annual Evaporation

MAP Mean Annual Precipitation

MAR Mean Annual Runoff

MIPI Midgley & Pitman Method

NWA The South African National Water Act, 1998 (Act No. 36 of 1998)

RM3 Rational Method Alternative 3

RMF Regional Maximum Flood

SDF Standard Design Flood

Tc Time of Concentration

WR2012 Water Resources of South Africa 2012

WMA Water Management Area

WUL Water Use Licence

WULA Water Use Licence Application


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LIST OF DEFINITIONS

Term Definition

Catchment A catchment defines an area from which water will naturally drain to a defined point.

Flood A flood results from heavy or continuous rainfall that does not infiltrate into soils, but runs off and collects to form extreme high flow rates in rivers or streams that may not be contained within river banks.

Hydrology

Hydrology describes a field of study that analyses natural cycles of water as it passes through the environment. Aspects analysed include rainfall, evaporation, transpiration and runoff. Hydrology also refers to the results of analysis of certain aspects of hydrological cycles, such as river flow, or likely peak floods.

Infiltration The movement of water from the land surface into the soil.

Percentiles

A statistical term indicating the value below which a given percentage of observations in a group of observations fall. For example, the 10th percentile is the value (or score) below which 10% of the observations may be found.

Runoff Surface runoff is defined as the water that finds its way into a surface stream channel without infiltration into the soil and may include overland flow, interflow and base flow.

Watercourse Watercourse refers to a river or spring, a natural channel in which water flows regularly or intermittently, a wetland, lake or dam into which, or from which water flows, and any collection of water.

WR2012

The WR2012 model and database describes the water resources of South Africa, Lesotho and Swaziland. It is the culmination of a number of water resource appraisals that have been carried out over the past four decades (WRC, 2015).


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EXECUTIVE SUMMARY

GCS Water and Environment (Pty) Ltd (GCS) has been appointed by Triplo4 Sustainable

Solutions (Pty) Ltd (Triplo4) to undertake a hydrological, flood line study and surface water

monitoring plan study for a Housing Estate Development in Bellair (The Bellair Development).

The Bellair Development is located in the eThekwini Metropolitan area in the KwaZulu-Natal

Province, South Africa. The Bellair Residential Development project entails the construction

of a series of residential units on two properties. The hydrological and flood line assessment

is a safety evaluation for the housing development, to aid the protection of natural resources,

and is a requirement for a Water Use License Application (WULA).

Baseline Hydrology and Climate

The climate at the Bellair Development site is described as warm and temperate with a

Koppen-Geiger climate classification of Cfa (fully humid and hot summer). Rainfall for the

site is based on 79 years of records at the nearby Louis Botha rainfall gauge (SAWS station:

04808 W) and historical records indicate a long-term average rainfall of 967 mm per annum.

Evaporation data used for this site is based on the 1 200 mm per annum Symons-Pan

evaporation and Evaporation Zone 22A (WRC, 2015).

Runoff from natural (unmodified) catchments in this area is simulated in WR2012 as being

equivalent to 219 mm per annum over the surface area. The design rainfall depths were

obtained from the Louis Botha rain gauge to represent the Bellair Development site in order

to calculate the design flood peaks as input into the flood line calculations.

Flood Lines

Flood lines were calculated for two drainage areas in the proximity of the Bellair

Development site for the 1:50-year and 1:100-year recurrence intervals. Some parts of the

Bellair Development site were found to be within the calculated flood lines. The Bellair

Development will trigger activities under Section 21(c) (crossing a watercourse) and 21(i)

(impeding or diverting flow) of the South African National Water Act (36 of 1998), which

require the application for a Water Use Licence (WUL). It is also important to stress that

there is risk of the development being flooded during flood events. The flood lines calculated

result in the Bellair Development being against the guidleines given by the CSIR (no

development should occur within a defined 1:50-year flood line of a river) and the eThekwini

Municipality (a development is not supported within the 1:100-year flood line).


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Recommendations

To improve the accuracy of the flood lines for construction purposes, it is recommended that

the flood lines be recalculated using more detailed contour data and signed off by a civil

engineer. It is advised that the Bellair Development take the abovementioned legislative

guidelines into consideration when planning for final construction and operational activities

- in particular the placement of infrastructure.

Triplo4 Sustainable Solutions Bellair Development

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CONTENTS PAGE

1 INTRODUCTION .......................................................................................................................... 1

2 SCOPE OF WORK ........................................................................................................................ 2

3 METHODOLOGY ......................................................................................................................... 3

3.1 BASELINE CLIMATE AND HYDROLOGY ................................................................................................. 3 3.2 FLOOD LINES ................................................................................................................................ 3

3.2.1 Legislative and Policy Framework ..................................................................................... 3 3.2.2 Design Flood Peaks ........................................................................................................... 4

3.3 SURFACE WATER MONITORING PLAN ................................................................................................ 8 3.4 SOFTWARE ................................................................................................................................... 8

4 BASELINE HYDROLOGY AND CLIMATE ...................................................................................... 10

4.1 CLIMATE .................................................................................................................................... 10 4.2 CATCHMENT CHARACTERISTICS AND DELINEATION ............................................................................. 12 4.3 RUNOFF ASSESSMENT .................................................................................................................. 14 4.4 DESIGN RAINFALL ........................................................................................................................ 16

5 FLOOD LINES ............................................................................................................................ 17

5.1 DESIGN FLOOD PEAKS .................................................................................................................. 17 5.2 FLOOD LINE RESULTS .................................................................................................................... 17

6 SURFACE WATER MONITORING PLAN ...................................................................................... 20

6.1 PROPOSED MONITORING LOCATIONS AND MONITORING FREQUENCY...................................................... 20 6.2 APPLICABLE PARAMETERS AND STANDARDS ...................................................................................... 21

7 CONCLUSIONS .......................................................................................................................... 23

8 RECOMMENDATIONS ............................................................................................................... 24

9 REFERENCES ............................................................................................................................. 25

LIST OF FIGURES

Figure 1-1: Locality of the Bellair Development ...................................................... 1 Figure 3-1 Summary of the flood line methodology .................................................. 7 Figure 4-1 Monthly rainfall distribution for the Bellair Development (WRC, 2015) ............ 11 Figure 4-2: Monthly evaporation distribution (Symons Pan) for the Bellair Development (WRC, 2005) ......................................................................................................... 11 Figure 4-3: Delineated sub-catchments for the project area ..................................... 13 Figure 4-4: Natural runoff distribution for quaternary catchment U60F (WRC, 2015) ........ 14 Figure 4-5: Monthly runoff distribution for the Bellair Development site ....................... 15 Figure 5-1: Flood line extent for the Bellair Development Residential Development ........ 19 Figure 6-1: Proposed Surface Water Monitoring Plan ............................................... 22

LIST OF TABLES

Table 3-1: Manning’s roughness coefficients (n) assumed for this study ......................... 5 Table 4-1: Identified catchment areas. ............................................................... 12 Table 4-2: Design Rainfall ................................................................................ 16 Table 5-1: Summary of the peak flows calculated for the study ................................. 17 Table 6-1: Proposed monitoring programme and recommended sampling frequencies ...... 20 Table 6-2: List of parameters quarterly analysis .................................................... 21 Table 6-3: List of parameters for annual analysis ................................................... 21


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LIST OF APPENDICES

APPENDIX A ..................................................................................................................................... 26


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1 INTRODUCTION

GCS Water and Environment (Pty) Ltd (GCS) has been appointed by Triplo4 Sustainable

Solutions (Pty) Ltd (Triplo4) to undertake a hydrological, flood line and surface water

monitoring plan study for the Bellair Housing Development (The Bellair Development). The

Bellair Development is located in the southern area of the city of Durban (eThekwini

Municipality) in the KwaZulu-Natal Province, South Africa. The Bellair Development is

situated in quaternary catchment U60F (see Figure 1-1).

The Bellair Development project entails the construction of a series of residential units on

two properties in the Bellair suburb of KwaZulu-Natal. The total development area is

approximately 5.2 ha.

The hydrological, flood line and surface water monitoring plan assessment makes up a part

of a safety evaluation for the housing development, to aid in the protection of natural

resources, and is a requirement for a Water Use License Application (WULA). This report

presents the results of this study.


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Figure 1-1: Locality of the Bellair Development


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2 SCOPE OF WORK

GCS and Triplo4 negotiated a scope of work for this specialist study which includes:

1. Information sourcing/literature review:

o A review of existing information was conducted.

2. Hydrology – the following was assessed:

o General climate and rainfall;

o Catchment characteristics and delineation; and

o Mean Annual Runoff (MAR) analyses.

3. A flood line assessment was undertaken that included:

o 1:50-year and1:100-year flood line calculations using HEC-GeoRAS and HEC-

RAS software;

o Mapping of flood lines together with the proposed infrastructure in order to

identify any potential encroachment.

4. Surface water monitoring plan:

o A surface water monitoring plan will be suggested by identifying sampling

points in affected and surrounding watercourses, and

o By recommending a sampling frequency and chemical suite.

5. A summary report was compiled detailing all the above listed activities.


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3 METHODOLOGY

The methodology that was adopted during this study is described below.

3.1 Baseline Climate and Hydrology

The climate of the Bellair Development was investigated. This was achieved by obtaining

climate data from the South African Weather Service (SAWS) weather station 0240808 W (Louis

Botha) and from the WR2012 database (WRC, 2015).

Sub-catchments of river systems and drainage areas around the site area were reviewed using

5 m topographical contour data (obtained from RSA National Geospatial Institute 1:50 000

Topographical Series: map code 2930 DD) (RSA National Geospatial Institute, 2013) and used

for natural sub-catchment delineation.

Monthly unit runoff distributions were calculated and it has been accepted that runoff

simulated in WR2012 for Quaternary Catchment U30E (see Figure 4-4) adequately represents

local conditions, as the upstream part of the catchment is in a natural state (WRC, 2015).

3.2 Flood Lines

Flood lines on river sections were calculated to evaluate risks associated with potential

flooding of infrastructure and protection of natural resources.

3.2.1 Legislative and Policy Framework

One of the main concerns in South Africa is the sustainability of water provision, and the costs

associated with the prevention and remediation of pollution in a country with a low average

rainfall. The National Water Act, 1998 (Act No. 36 of 1998) (NWA) addresses South Africa’s

water challenges (Section 27 of the Constitution of the Republic of South Africa, 1996).

Land use, development or activities near watercourses and/or wetlands must be conducted in

line with the NWA and these activities should be aligned with the objectives envisioned by the

Act. The NWA regulates the use of water and any activities related to the use of water. The

Act also sets out certain guidelines related to flood line management and are the leading

legislation for this study. Section 144 of the NWA places restrictions on the location of

residential developments or townships and states that no person may establish a township

within the 1:100-year flood line.


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Additionally, for this study the guidelines given by the Council for Scientific and Industrial

Research (CSIR), The Ecologically Sound Urban Development: Town Planning and Townships

Ordinance (Ordinance 15 of 1986) were applied. This guideline states that no development

should occur within a defined 1:50-year flood line of a river. The guidelines further state that

the flood line area should be extended by 32m where the 1:50-year flood line is less than 62m

in total (CSIR, 2005), which is the case in this study.

The Bellair Development is located within the direct confines of the eThekwini Municipality.

The eThekwini Municipality prescribes further guidelines; The Development Assessment

Guidelines published by the eThekwini Municipality (eThekwini Municipality, 2010). These

guidelines suggest that a minimum buffer of 20 m is required between the footprint of

development and the top of the bank of a stream or drainage line. It furthermore suggests

that a development is not supported within the 1:100-year flood line.

A consistent and conservative approach adopted within all of the abovementioned pieces of

legislation is the demarcation of both the 1:50-year and 1:100-year flood lines. The 1:50-year

and 1:100-year flood lines have therefore been plotted within this study. The NWA was used

as the leading legislation for this study and was followed implicitly. Section 144 of the NWA

places restrictions on the location of residential developments or townships and states that

no person may establish a township within the 1:100-year flood line.Additionally the CSIR

guidelines described earlier in this section of the report were followed and the eThekwini

Municipality guidelines were adhered-to.

The abovementioned legislation guided the minimum requirements for placement of

infrastructure pertaining to the Bellair Development in relation to a natural watercourse.

3.2.2 Design Flood Peaks

In order to produce peak runoff input, four Methods were used to determine design flood peaks

for the delineated catchments at the Bellair Development. These methods are the Rational

Method Alternative 3 (RM3), the Standard Design Flood (SDF) Method, the Midgley & Pitman

(MIPI) Method and the Regional Maximum Flood (RMF) method. The Design Rainfall Estimation

Software (Smithers & Schulze, 2000) was utilised in the RM3 to calculate peak flows for the

site. The rainfall depths with durations corresponding to the Time of Concentration (Tc) for

each catchment were used to calculate peak flows for the particular catchments. The design

rainfall depths, which were obtained from the Design Rainfall Software (Smithers & Schulze,

2000), are presented in Table 4-2. The underlying assumption is that the largest possible peak

flow is obtained when the storm rainfall event has a duration equal to the time required for

the whole catchment to contribute runoff at the outlet.

A short description of the above-mentioned methods is given below.


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Rational Method

The Rational Method was developed in the mid-19th century and is one of the most widely used

methods for the calculation of peak flows for small catchments (<15 square kilometres (km2).

The formula indicates that Q = CIA, where I is the rainfall intensity, A is the upstream runoff

area and C is the runoff coefficient. Q is the peak flow. Point precipitation (for the designated

T) is taken from Error! Reference source not found. of the Baseline Receiving Conditions of

the site section.

Standard Design Flood Method

The Standard Design Flood (SDF) method was developed specifically to address the uncertainty

in flood prediction under South African conditions (Alexander, 2002). The runoff coefficient

(C) is replaced by a calibrated value based on the subdivision of South Africa into 26 regions

or Water Management Areas (WMAs). The design methodology is slightly different to that of

the Rational Method and looks at the probability of a peak flood event occurring at any one of

a series of similarly sized catchments in a wider region, while other methods focus on point

probabilities.

Empirical Methods

Empirical methods such as the Midgley and Pitman (MIPI) and Regional Maximum Floods (RMF)

are based on correlation between peak flows and some catchment characteristics. Regional

parameters are then mapped out for South Africa. These methods are mostly suitable for

medium to large catchments (SANRAL, 2013).

3.2.2.1 Flood Line Calculation

The HEC-RAS model simulates the total energy of water by applying basic principles of mass,

continuity and momentum as well as roughness factors between all cross sections. A height

was calculated at each cross-section, which represents the level to which water will rise at

that section, given the design peak flows. This was calculated for the 1:50- and 1:100-year

peak flows on all river sections.

Analyses were performed by modelling flows at the sub-catchment outlet of particular stream

or channel sections first, moving upstream. Manning’s roughness coefficients (n) for the

channels were set at 0.06, and those for river banks were determined to be 0.075 (see Table

3-1). These values were chosen as these values are typically representative for channels and

stream banks in the greater Durban area.

Table 3-1: Manning’s roughness coefficients (n) assumed for this study

RIVER REACH SECTION N

Channel 0.06

River Bank 0.075


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These coefficients were selected based on the Cowan Theory (Cowan, 1956) according to the

following equation:

𝑛=(𝑛𝑏+𝑛1+𝑛2+𝑛3+𝑛4) 𝑚 (3.1)

Where nb is a base value of n for a straight, uniform, smooth natural channel:

n1 is a correction factor for the effect of surface irregularities;

n2 is a value depicting channel cross sectional area variations in shape and size;

n3 is a value for flow obstructions in the channel;

n4 is a value for vegetation and flow conditions; and

m is a correction factor for the meandering of the channel.

Physiographic characteristics of assessed channels were used to estimate roughness

adjustment factors, as described in the aforementioned equation (Cowan, 1956). A summary

of the methodology used in the hydraulic modelling process is presented in Figure 3-1

.


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Figure 3-1 Summary of the flood line methodology

The following limitations were experienced and assumptions have been made in this specialist

study:


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No flow data against which the runoff calculations might be calibrated were available.

The runoff volumes were therefore calculated theoretically (see Section 4.3);

The Manning roughness coefficients (n) were estimated by comparing the vegetation

and nature of the channel surfaces to published data (Hick & Mason, 1991) (Chow,

1959); and

Only 5 m topographical contour data (obtained from RSA National Geospatial Institute

1:50 000 Topographical Series: map code 2930DD) were available and used as input

for the flood line calculations.

3.3 Surface Water Monitoring Plan

The NWA Act explicitly recognises the need for the integrated management of all aspects of

water resources and introduced the concept of Integrated Water Resource Management

(IWRM), comprising all aspects of the water resource, including water quality, water quantity

and the aquatic ecosystem quality (quality of the aquatic biota and in-stream and riparian

habitat).

A surface water quality monitoring programme for the Bellair Development will therefore be

required and developed in accordance with the ISO 5667 – 01 -2006 standard (ISO, 2006) and

The Best Practice Guidelines G3: Water Monitoring Systems (DWA, 2006c). The monitoring

programme will assists with overall water management at the site, including but not limited

to:

Preventing pollution and thereby protecting the receiving water environment;

Developing an understanding of the current water quality on site and monitoring how

it changes over time, and

Assessing performance of pollution prevention measures, i.e. compliance with any

license conditions that may be imposed in the future.

The monitoring programme should be designed according to the on-site developments and

developmental footprint as well as a possible future Water Use License (WUL) or other permit

requirements.

3.4 Software

Software used in the study includes the following:

ArcView 10.1 (ESRI, 2012) for Geographic Information Systems (GIS) work and

mapping;

Hec-RAS V4.1.0 (US Army Corps of Engineers, 1995) modelling software for hydraulic

calculation of flow depths;


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Hec GEO-RAS software for preparation of hydraulic geometry input files for Hec-RAS

model; and

Results of the WR2012 of South Africa Study (WRC, 2015) used for base-line runoff

data.


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4 BASELINE HYDROLOGY AND CLIMATE

The Bellair Development is to take place in the eThekwini Metropolitan Municipality (in the

suburb of Bellair) situated in the province of KwaZulu-Natal of South Africa. The development

is located within the U60F Quaternary Catchment of the Mvoti and Mzimkulu Water

Management Area (WMA). The predominant land use surrounding the site is residential. The

location of the Bellair Development site is shown in Figure 4-3.

4.1 Climate

The climate at Bellair Development is described as warm and temperate with a Koppen-Geiger

climate classification of Cfa (fully humid and hot summer) (Conradie, 2012). The vegetation

biome that dominates this area is Eastern Coastal Bushveld (Kruger, 2004).

The area falls within the summer rainfall zone and receives most of its annual rainfall during

the period from October to March. The Mean Annual Precipitation (MAP) was determined at

967 mm by verifying Louis Botha rainfall gauge (SAWS station: 0240808 W) and using WR2012

see (Figure 4-1). This rain gauge is located 9 kilometres south of the Bellair Development.

Mean Annual Evaporation (MAE) is 1 200 mm based on Symons Pan (S-Pan) evaporation (WRC,

2015) (see Figure 4-2).

The percentiles referred-to in the underlying image indicate the value below which a given

percentage of observations in a group of observations fall. For example, the 10th percentile

is the value of rainfall below which 10% of the monthly rainfall may be found for the Bellair

Development site.


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Figure 4-1 Monthly rainfall distribution for the Bellair Development (WRC, 2015)

Figure 4-2: Monthly evaporation distribution (Symons Pan) for the Bellair Development (WRC, 2005)


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4.2 Catchment Characteristics and Delineation

The total drainage area of the site was divided into sub-catchments based on the topography

of the area. A total of three sub-catchments were delineated and the areas of these are

presented in Table 4-1 and Figure 4-3. Catchments were selected focusing on their proximity

to the proposed Bellair Development as well as their impact on the design floods of the area.

Table 4-1: Identified catchment areas.

CATCHMENT AREA (km2)

2 0.23

3 0.10

When interrogating the available topographic data for the area, it was observed that there is

a watercourse located in close proximity to the western portion of the proposed Bellair

Development and runs adjacent to the National Road designated as the N2. This water course

and catchment is shown in Figure 4-3 as Catchment 1. The watercourse has been altered by

SANRAL to convey stormwater generated away from the N2. This is achieved by the use of

concrete channels and has been designed and sized by SANRAL. As topographical data only

allows for natural water course delineation, this watercourse could not be modelled.


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Figure 4-3: Delineated sub-catchments for the project area


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4.3 Runoff Assessment

Runoff from natural (unmodified) catchments in this area is simulated in WR2012 as being

equivalent to 159 millimetres per annum (mm/annum) over the surface area (WRC, 2015).

This is equal to approximately 16% of the MAP. The natural runoff distribution for Quaternary

Catchment U60F is shown in Figure 4-4.

Figure 4-4: Natural runoff distribution for quaternary catchment U60F (WRC, 2015)

On the Bellair Development site, it is thought that the proposed activities will significantly

alter the natural runoff pattern due to catchment urbanisation. Levelled surfaces and sub-

surface compacted layers are likely to limit infiltration. Surfaces are smoother and will

facilitate increased surface runoff from storm events. These factors were incorporated into a

simulation of runoff for the Bellair Development, which indicates a runoff pattern as shown in

Figure 4-5.

Analysis of trends of runoff in the region estimated that runoff from the Bellair Development

site is likely to have increased to an approximate 50% of rainfall per annum.


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Figure 4-5: Monthly runoff distribution for the Bellair Development site


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4.4 Design Rainfall

The design rainfall depths were obtained for the site in order to calculate the design flood

peaks. These values were obtained using the Design Rainfall Estimation software (Smithers &

Schulze, 2000). This software analyses all the rain gauges in South Africa for data and tabulates

the design rainfall depths for various return periods. The design rainfall depths that were used

for this study were taken from the Louis Botha rainfall gauge (SAWS station: 0240808 W). This

station is approximately 9 km south of the Bellair Development. The design rainfall depths

used in the calculation of the design flood peaks are presented in Table 4-2.

Table 4-2: Design Rainfall

Duration Return Period (years)

(min/hr/day) 2 5 10 20 50 100 200

5 min 9.5 14.2 17.9 21.9 28 33.2 39

10 min 14.6 21.9 27.6 33.9 43.2 51.2 60.2

15 min 18.9 28.3 35.6 43.7 55.7 66 77.7

30 min 25.4 38.1 48 58.8 75 88.9 104.6

45 min 30.2 45.3 57.1 70 89.2 105.8 124.5

1 hr 34.2 51.3 64.6 79.2 100.9 119.8 140.9

1.5 hr 40.7 61.1 76.9 94.2 120.1 142.5 167.7

2 hr 46.1 69.1 87 106.6 135.9 161.3 189.7

4 hr 56.7 85 107.1 131.2 167.3 198.4 233.4

6 hr 64 96 120.9 148.1 188.8 224 263.5

8 hr 69.8 104.6 131.7 161.4 205.8 244.1 287.2

10 hr 74.6 111.8 140.8 172.5 220 261 307

12 hr 78.8 118.1 148.7 182.2 232.3 275.6 324.2

16 hr 85.8 128.7 162.1 198.6 253.2 300.3 353.3

20 hr 91.8 137.5 173.3 212.3 270.6 321.1 377.7

24 hr 96.9 145.2 183 224.2 285.8 339 398.9

1 day 80.6 120.9 152.3 186.5 237.8 282.1 331.9

2 days 101.5 152.1 191.6 234.7 299.2 355 417.6

3 days 116 173.9 219.1 268.4 342.2 406 477.7

4 days 122.1 183.1 230.6 282.5 360.2 427.3 502.8

5 days 127.1 190.5 240 294 374.8 444.7 523.1

6 days 131.3 196.8 247.9 303.7 387.2 459.3 540.4

7 days 134.9 202.2 254.8 312.1 398 472.1 555.4


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5 FLOOD LINES

The following describes a brief summary of calculated flood lines for the defined watercourse

in the vicinity of the proposed Bellair Development.

5.1 Design Flood Peaks

Peak flows for the 1:50- and 1:100-year storm events were calculated for five delineated

catchments. The calculated peak flows can be seen in Table 5-1 and calculation sheets are

provided in Appendix A.

Table 5-1: Summary of the peak flows calculated for the study

Catchment

Method

Rational SDF Midgley and Pitman RMF

1:50yr 1:100yr 1:50yr 1:100yr 1:50yr 1:100yr 1:50yr 1:100yr

(m3/s)

1 16.53 21.46 20.97 26.97 11.34 19.09 17.94 19.75

2 7.73 9.59 9.77 12.56 7.42 12.50 10.52 11.58

The design flood peaks for the SDF method (for all catchments) are higher than the RM3 and

the MIPI method, but within the same order of magnitude. It was decided to use the peak

flows calculated by the RM3 method as input into the HEC-RAS model. This was due to the

catchment areas all being considerably smaller than the 15 km2 size limit for the RM3 (SANRAL,

2013) making the RM3 method the most suitable.

5.2 Flood Line Results

The flood lines calculated and plotted for the Bellair Development are shown in Figure 5-1.

Portions of all 3 erven of the Bellair Development site do fall within the two plotted flood-

lines and CSIR guidelines (see Figure 5-1). As seen below, there is a flooding risk to certain

portions of the housing development. Section 144 of the National Water Act (Act 36 of 1998)

states that no township may be established within the 1:100-year flood line. The Bellair

Development is located within the 1:100-year flood as shown in Figure 5-1.


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The 1:50-year CSIR Guidelines line demarcates the 1:50-year flood line area of the relevant

streams. Certain portions of the 1:50-year flood lines were extended by 32m when the width

of the flood lines was less than 62m. As mentioned earlier in this section, portions of the

Bellair Development fell within these CSIR guidelines of flood lines for housing development.

In addition, the flood lines calculated show that the Bellair development falls within the 1:100-

year flood line which is against the guidelines prescribed by the eThekwini Municipality. These

guidelines are based upon those given by Section 144 of the NWA.

Calculated flood lines will trigger activities under Section 21(c) (crossing a watercourse) and

21(i) (impeding or diverting flow) of the NWA, which require the application for a Water Use

Licence (WUL).


16-0619 4 October 2016 Page 19

Figure 5-1: Flood line extent for the Bellair Development Residential Development


16-0867 4 October 2016 Page 20

6 SURFACE WATER MONITORING PLAN

This section describes the proposed surface water monitoring programme undertaken for the

proposed Bellair Development.

6.1 Proposed monitoring locations and monitoring frequency

Details of the proposed monitoring programme are presented in Table 6-2. Figure 6-1 shows

4 proposed locations for surface water monitoring for the Bellair Development. It is

recommended that samples are taken upstream and downstream of the development. It is

important to stress SW1 and SW2 must be the main sampling points of the proposed

programme.

It is recommended that the receiving environment close to the proposed site will be

monitored for water quality to establish a baseline water quality situation by monitoring on

a quarterly basis (see Table 6-1 and Figure 6-1)

Continuous monitoring at the discharge areas and receiving environment around the proposed

site is recommended after construction to enabling the process to determine possible impacts

upon completion of the project (see Table 6-2 and Table 6-3). This can be established by

sampling on a quarterly basis after construction of the Bellair Development at the proposed

locations. In addition, annual sampling should be undertaken to test for potential

hydrocarbons spills at the discharge points.

Ad-hoc monitoring is recommended during storm events at the sampling points. The

implementation of ad-hoc monitoring is seen as a protocol to assess water quality in between

the frequency based monitoring programme.

Table 6-1: Proposed monitoring programme and recommended sampling frequencies

Water Type Period Details Monitoring Frequency

Receiving Environment

Continuous Monitoring Operations

Sample points at the 4 in-stream localities (see Table 9-3 and Figure 9-1).

Quarterly


16-0867 4 October 2016 Page 21

6.2 Applicable Parameters and Standards

The water samples should be analysed for the parameters (listed in Table 6-2Error!

Reference source not found.) all samples should additionally be tested for hydrocarbons

owing to potential hydrocarbon spills from the (see Table 6-3).

Table 6-2: List of parameters quarterly analysis

pH at 22oC Potassium, K

Conductivity mS/m Total Alkalinity as

CaCO3

Total Dissolved Solids

(TDS) Bicarbonate, HCO3

Calcium, Ca Chloride, Cl

Magnesium, Mg (mg/l) Sulphate, SO4

Sodium, Na Nitrate, NO3

Aluminium (Al) Manganese (Mg)

Iron (Fe) Total Coliforms

The additional parameters which should be analysed for on an annual basis are presented in

Table 6-3.

Table 6-3: List of parameters for annual analysis

Hydrocarbons

BTEX-N

DRO

GRO

The water quality results should be compared to the limits specified in the latest WUL. If a

WUL is not available or limits for some parameters are not specified in the WUL, the following

guidelines and standards should be used, based on the activities associated with the Bellair

Development:

South African Water Quality Guidelines (2nd edition), Volume 1: Domestic Water Use

(Department of Water and Sanitation, 1996), and

SANS 241-1:2015, Drinking water Part 1: Microbiological, physical, aesthetic and

chemical determinants. Specifies the quality of acceptable drinking water, defined

in terms of microbiological, physical, aesthetic and chemical determinants (SANS,

2015).


16-0867 4 October 2016 Page 22

Figure 6-1: Proposed Surface Water Monitoring Plan


16-0867 4 October 2016 Page 23

7 CONCLUSIONS

The following conclusions were derived based on the findings of this study.

Portions of the Bellair Development site do fall within the flood lines plotted for the

1:50 and 1:100-year peak flows and are thus at risk of being flooded.

As the development is located within the eThekwini Municipality, the Bellair

Development is not compliant with the Development Assessment Guidelines.

Calculated flood lines will trigger activities under Section 21(c) and 21(i) of the NWA,

which require the application for a Water Use Licence (WUL).

Four surface water monitoring points are required post-development. These have been

chosen upstream and downstream of the Bellair Development.


16-0867 4 October 2016 Page 24

8 RECOMMENDATIONS

The following recommendations were derived based on the findings of this study:

To improve accuracy for construction level, it is recommended to provide a more

detailed topographical survey and re-do the flood line assessment. Accurate and

current topographical data are required to allow for the modelling, in a future study,

of Catchment 1 – this will allow for a more accurate and representation of the flood

hydrology of the Bellair Development.

It is advised that the Bellair Development take the abovementioned legislative

guidelines into consideration when deciding on the final construction and operational

activities - in particular the placement of infrastructure.

The proposed surface water monitoring plan should be followed as to ensure possible

impacts by the development on the surrounding surface water resources are

minimised.


16-0867 4 October 2016 Page 25

9 REFERENCES

Alexander, J. (2002). The Standard Design Flood. South African Institution of Engineers, 26-30.

Chow, V. (1959). Open Channel Hydraulics. New York: McGraw-Hill. Conradie, D. C. (2012). South Africa’s Climatic Zones: Today, Tomorrow. International Green

Building Conference and Exhibition. Future Trends and Issues Impacting on the Built Environment. Sandton, South Africa.

Cowan, W. (1956). Estimating hydraulic roughness coefficients. Agricultural Engineering Journal 377, 473-475.

CSIR. (2005). Guidelines for Human Settlement Design: Volume 2. Pretoria: CSIR Building and Construction Technology.

Department of Water and Sanitation. (1996). South African Water Quality Guidelines Volume 1 - Domestic Use. Pretoria: DWS.

DWA. (1996). South African Water Quality Guidelines (2nd edition), Volume 5: Agricultural Water Use: Livestock Watering.

ESRI. (2012, May). ArcView10.1. ESRI. eThekwini Municipality. (2010). Development Assessment Guidelines. Durban: eThekwini

Municipality. Hick, D., & Mason, P. (1991). Roughness characteristics of New Zealand Rivers. Water

Resources Survey Paper, 1-13. ISO. (2006). ISO 5667-1:2006 Water Quality – Sampling – Part 1: Guidance on the design of

Sampling Programmes and sampling Techniques. Kruger, A. (2004). Climate of South Africa. Climate Regions. WS45, South African Weather

Service, Pretoria,. RSA National Geospatial Institute. (2013). National Geo-spatial Information: NGI. Department

of Rural Development and Land Reform. SANRAL. (2013). South African Drainage Manual. Pretoria: SANRAL. SANS. (2015). SANS 241-1:2015, Drinking water Part 1: Microbiological, physical, aesthetic

and chemical determinants. Specifies the quality of acceptable drinking water, defined in terms of microbiological, physical, aesthetic and chemical detenninands.

Smithers, J. C., & Schulze, R. E. (2000). Design Rainfall Estimation. UKZN. US Army Corps of Engineers. (1995). HEC RAS Hydraulic Modelling Software. Version 4.1.

California. WRC. (2005). Surface Water Resources of South Africa. WRC Report No. TT 382/08. Water

Research Commission of South Africa. WRC. (2015). http://www.waterresourceswr2012.co.za/resource-centre/. Retrieved from

Water Resources of South Africa, 2012 Study (WR2012).


16-0867 4 October 2016 Page 26

APPENDIX A

Design flood peak calculation sheets

Catchment 2

Date

Size of catchment (A) 0.229

Longest watercourse (L) 0.549

Average slope (Sav) 0.087 Rural (α) Urban (β) Lakes (γ)

Dolomite area (D%) 0 0.1 0.9 0

Mean annual rainfall(MAR) 993

% Factor Cs Description % Factor C2

0.00 0.05 0.00 Lawns

30.00 0.11 3.30 Sandy,flat<2% 0.08 0

30.00 0.20 6.00

Sandy,steep>7

%50 0.16 8

40.00 0.30 12.00Heavy s,flat<2% 0.15 0

100.000.66 21.30

Heavy

s,steep>7%50 0.3 15

% Factor Cp

Residential

Areas

0 0.05 0.00 Houses 100 0.5 50

0 0.1 0.00 Flats 0.6 0

50 0.2 10.00 Industry

50 0.3 15.00 Light industry 0 0.6 0

100 0.65 25.00 Heavy industry 0 0.7 0

% Factor Cv Business

7 0.05 0.35 City centre 0 0.8 0

40 0.15 6.00 Suburban 0 0.65 0

50 0.25 12.50 Streets 0 0.75 0

3 0.3 0.90 Max flood 1

100 0.75 19.75 Total (C2) 200 73

0.526 hours hours

Return Period (years) 2 5 10 20 50 100 PMF

0.723 0.723

0.723 0.723

0.95 1

0.687 0.723

0.687 0.723


40.43436684 49.86688274

377.73 465.8409142

1.000 1.000

377.725 465.841


16.53 21.46

Surface slope

Permeability

m/m

Total

Thick bush & plantation

Semi-permeable

km Area distribution factors

URBAN

%

mm

Rural

Vleis and pans (<3%)

Flat areas (3 - 10%)

Hilly (10 - 30%)

Steep Areas (>30%)

Permeable

km2 Rainfall region 2

RATIONAL METHODDescription of catchment 2

River detail -

Calculated by Craig Orchard 2016-09-15

Physical characteristics

Peak flow (m3/s)

Rainfall

Use Defined watercourse

0.107

Run-off coefficient

Run-off coefficient, C1

Adjusted for dolomitic areas, C1D

Adj factor for initial saturation, Ft

Adjusted run - off coefficient, C1T

Combined run - off coefficient, CT

Area reduction factor (%),ARFT

Average intensity (mm/hour),IT

Light bush & farm-lands

Grasslands

Point rainfall (mm), PT

Point Intensity (mm/h), P it

No vegatation

Very permeable

Overland flow Defined watercourse

Total

Impermeable

Total

Time of concentration (TC)

Vegetation

385.02

1000

87.0

AV

cS

LT

467.0

604.0

av

CS

rLT


16-0867 4 October 2016 Page 27

Date

Size of catchment (A) 0.229 15 days

Longest watercourse (L) 0.549 6.423 minutes

Average slope (Sav) 0.087

SDF Basin

2-year return period rainfall (M) 76

Weather Service Station MAP 910 mm

Weather Service Station no. Coordinates

2 5 10 20 50 100 200

1 day 235 284

Return Period (years), T 2 5 10 20 50 100 200

51.6 59.9

0.95 0.95

455.9 529.0

Calibration factors C2 (%)


0 0.84 1.28 1.64 2.05 2.33 2.58

0.72 0.8

20.97 26.97

Duration

Return Period (years)

Return period factors (YT)

Run-off coefficient, CT

Peak flow (m3/s)

Rainfall

Point precipitation depth (mm) Pt,T



Run-off coefficient

15 C100 (%) 80

Days of thunder per year (R)

km Time of concentration, t

Newlands

240269 27 °09' (Lat) & 30°35' (Long)


TR102 n-day rainfall data

STANDARD DESIGN FLOOD METHODDescription of catchment 2

River detail

m/m Time of

concentration

, Tc

0.107024

mm


km2

467.0

604.0

av

CS

rLT

Date

Size of catchment (A) 0.229 4


Length to catchment centroid 0.452

Average Slope 0.087

Mean annual rainfall (MAP) 993

10 20 50 100

0.95 1.6

11.34 19.09

0.447 0.492

17.94 19.75

40.14

QT/QRMF ratios

Peak flow based on QT/QRMF ratios

QRMF based on Kovacs

m/m

mm

Return period (years)

Constant value for KT

Peak Flow (QT) based on Midgley and Pittman


km2 Kovacs Region

km Catchment parameter with

regards to reaction time © 0.27km


MIDGLEY AND PITMAN EMPIRICAL METHODDescription of catchment 2

River detail -


16-0867 4 October 2016 Page 28

Catchment 3

Date

Size of catchment (A) 0.097


Average slope (Sav) 0.099 Rural (α) Urban (β) Lakes (γ)

Dolomite area (D%) 0 0.1 0.9 0

Mean annual rainfall(MAR) 993

% Factor Cs Description % Factor C2

0.00 0.05 0.00 Lawns

30.00 0.11 3.30 Sandy,flat<2% 0.08 0

30.00 0.20 6.00

Sandy,steep>7

%50 0.16 8

40.00 0.30 12.00Heavy s,flat<2% 0.15 0

100.000.66 21.30

Heavy

s,steep>7%50 0.3 15

% Factor Cp

Residential

Areas

0 0.05 0.00 Houses 100 0.5 50

0 0.1 0.00 Flats 0.6 0

50 0.2 10.00 Industry

50 0.3 15.00 Light industry 0 0.6 0

100 0.65 25.00 Heavy industry 0 0.7 0

% Factor Cv Business

7 0.05 0.35 City centre 0 0.8 0

40 0.15 6.00 Suburban 0 0.65 0

50 0.25 12.50 Streets 0 0.75 0

3 0.3 0.90 Max flood 1

100 0.75 19.75 Total (C2) 200 73

0.374 hours hours


0.723 0.723

0.723 0.723

0.95 1

0.687 0.723

0.687 0.723


25.42673208 29.9665921

417.54 492.0854977

1.000 1.000

417.536 492.085


7.73 9.59

Surface slope

Permeability

m/m

Total

Thick bush & plantation

Semi-permeable

km Area distribution factors

URBAN

%

mm

Rural

Vleis and pans (<3%)

Flat areas (3 - 10%)

Hilly (10 - 30%)

Steep Areas (>30%)

Permeable

km2 Rainfall region 2

RATIONAL METHODDescription of catchment 3

River detail -



Peak flow (m3/s)

Rainfall

Use Defined watercourse

0.061

Run-off coefficient

Run-off coefficient, C1

Adjusted for dolomitic areas, C1D

Adj factor for initial saturation, Ft

Adjusted run - off coefficient, C1T

Combined run - off coefficient, CT



Light bush & farm-lands

Grasslands

Point rainfall (mm), PT

Point Intensity (mm/h), P it

No vegatation

Very permeable

Overland flow Defined watercourse

Total

Impermeable

Total

Time of concentration (TC)

Vegetation

385.02

1000

87.0

AV

cS

LT

467.0

604.0

av

CS

rLT


16-0867 4 October 2016 Page 29

Date

Size of catchment (A) 0.097 15 days

Longest watercourse (L) 0.282 3.654 minutes

Average slope (Sav) 0.099

SDF Basin

2-year return period rainfall (M) 76

Weather Service Station MAP 910 mm

Weather Service Station no. Coordinates

2 5 10 20 50 100 200

1 day 235 284


31.6 36.6

0.97 0.97

502.2 582.8

Calibration factors C2 (%)


0 0.84 1.28 1.64 2.05 2.33 2.58

0.72 0.8

9.77 12.56

Duration

Return Period (years)

Return period factors (YT)

Run-off coefficient, CT

Peak flow (m3/s)

Rainfall

Point precipitation depth (mm) Pt,T



Run-off coefficient

15 C100 (%) 80

Days of thunder per year (R)

km Time of concentration, t

Newlands

240269 27 °09' (Lat) & 30°35' (Long)


TR102 n-day rainfall data

STANDARD DESIGN FLOOD METHODDescription of catchment 3

River detail

m/m Time of

concentration

, Tc

0.060924

mm


km2

467.0

604.0

av

CS

rLT

Date

Size of catchment (A) 0.097 4


Length to catchment centroid 0.250

Average Slope 0.099

Mean annual rainfall (MAP) 993

10 20 50 100

0.95 1.6

7.42 12.50

0.447 0.492

10.52 11.58

23.54

QT/QRMF ratios

Peak flow based on QT/QRMF ratios

QRMF based on Kovacs

m/m

mm

Return period (years)

Constant value for KT

Peak Flow (QT) based on Midgley and Pittman


km2 Kovacs Region

km Catchment parameter with

regards to reaction time © 0.43km


MIDGLEY AND PITMAN EMPIRICAL METHODDescription of catchment 3

River detail -

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