EIS 137

Coffs Harbour coastal planning study.

NSW DEPT PR1AR? INDUSTRIES

11 11~~ 1~~ 1I

AA056928

Cof fs Harbour Coastal Planning

Study

RLUtEiIIFLE PA-I1III 4 Hydrology

NSW Planning & Environment Commission Grafton Office January, 1980

' 79/27

COFFS HARBOUR COASTAL PLANNING STUDY

Working Paper 4: HYDROLOGY

Prepared by P. Mitchell

This paper is published for the information of and assessment by Council's Liaison Committee, the Planning and Environment Commission's Review Committee and the Study Team.

The paper is accompanied by a map at 1:50,000 scale which is held in the Grafton Office of the Planning and Environment Commission. This map shows flood prone land.

NSW Planning and Environment Commission Grafton Office January 1980 reprinted August 1980. 79/2 7

ISBN 720 4528 7

iORE WORD

This paper is the fourth in a proiected series of fifteen arising from the Coffs Harbour Coastal Planning Study, initiated by the State Government to assist in the formulation of the Coffs Harbour sub-Regional Environmental Plan.

It describes various aspects of water resources in the study area and advises on land management practices capable of reducing pollution of the sub-region's waterways.

The Government recommends a reading of all papers in the series to those interested in environmentally sound manage-ment of the State's coastline.

ERIC BEDFORD Ninister for Planning and Environment.

A. SURFACE WATER 5

1. IntroductiOn 5

2. Quantity 5

3. variability of Stream Flow 6

4. Surface Water Quality 7

5. Flooding 11

B. GROUNDWATER HYDROLOGY 14

1. Groundwater Quantity 14

unconsolidated Sediments

Bedrock Geollogy

2. Groundwater Quality 15

3. Site Selection for Septic Tanks 16

4. Site Selection for Waste Disposal 17

VJXPS

Location

Study Area

. Groundwater Bearing Potential 18

I. Hydrology - Areas Subject to 19

Surface Water Inundation

TABLE S

i. Average Annual Discharges 5

variability of Stream Flow 6

Water Quality in Boambee Creek 8

REFERENCES

LOCATION MAP

MAP1

RED ROCK

d 0

ARRAWARRA

MUL LA WAY

) WOOLGOOLGA

SANDY BEACH 0

EMERALD BEACH

MOONEE BEACH

SAPPHTRE BEACH

KORORA BAY Q

COFFS HARBOUR

0

Airport

SAWTELL

0 0

STUDY AREA

Bundageree Head

MAP2

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A. SURFACE WATER

Introduction

The study area is traversed by a number of streams which rise in the coastal ranges and flow across narrow alluvial plains to the Sea. Generally the streams are small but they perform a variety of important functions, including being a source of town and agricultural water supply, and acting as recreational resources which allow activities such as swimming, fishing and in the larger streams, boating. With their associated wetlands they also provide habitat for fish, tortoise, platypus and a variety of birds.

Many of the streams end in lagoons and swamps behind the beach and dune systems. This is partially a consequence of their mouths beinq frequently blocked by accumulations of sand and sediment. Another characteristic is that the tidal influence in streams is restricted to the lower coastal reaches. These characteristics, combined with others mentioned elswhere in the paper, make the streams and lagoons highly vulnerable to pollution.

Quantity

Average surface water runoff for the study area is more than double the average runoff for coastal New South Wales and nearly nine times the average for the State per unit area per year. This is fundamentally a consequence of the high annual rainfall. Although there has been monitoring of only one stream in the study area, woolgootyCreek, data for a number of other streams within Coffs Harbour Shire is available to illustrate typical surface water discharge rates. Generally these are low and the volumes are insufficient to support large settlements. This intormation is presented in Table 1 below.

Table 1: Average Annual Discharges

Stream Station Catchment Mean Annual Discharge area (Km2) Ml Depth of

runoff from Catchment (mm)

oolgoo1qa Creek Woolqoolqa 10.9 7,200 660

Crara River Karangi No.2 132 183,000 1,390

Little Nymboida River Timrnsvale .1 32,000 1,030

Bobo Creek Bobo Nursery 80 90,000 1,130

TJrumliluni Creek Dairyville 18 37,000* 2,050

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* Only two complete years of records have been computed and this figure has been strongly influenced by the 197E flood year.

3. Variability of Stream Flow

This has relevance to the probable extent to which surface water resources can be utilized without the construction of storage works and also to water quality management as it indicates the degree of water turnover in streams. Within the study area records of flow are only available for woolgoolga Creek but figures are available for a number of similar creeks elsewhere in Cofts Harbour Shire. Stream flow data is presented in Table 2.

Table 2: Variability of Stream Flow

Stream Station Complete Recorded Discharges Years of (Ml/d Computed Records Max. Mm. Mean.

oo1qoo1qa Creek Woolqoolga 8 8,800 0 20

Orara River Iarangi No.2 19 61,200 1 500

Little Nymboida River Timmsvale 12 22,800 0.5 87

Hobo Creek Hobo Nursery 21 80,700 7 250

Ururnbilum Creek Dairyville 2 101800 0.5 100

A substantial degree of flow variability is evident. High flows occur after periods of heavy rain but are generally of short duration. Contrasting with this, woolgoolga Creek has ceased to flow on sevral occasions with conditions of no flow lasting for up to three months. This condition has not occurred in other creeks but very low flows have been recorded.

Thus it is apparent that constructiOn of storage structures will be necessary to enable dependence on coastal streams for water supply. In addition, extreme care is warranted in water quality management as potntial pollutants delivered to streams by irrigation and domestic runoff will tend to accumulate to unacceptable levels in times of low flow.

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L • Surface Water Qualit

Surface waters have a varying ability to absorb potential pollutants. This is largely dependent upon the volume of stream flow, the rate at flow in a stream, the degree of interchange between a stream and the ocean and water chemistry.

Within the study area pollution is derived from both urban and agricultural runoff. Urban runoff containing as it does oils, greases, detergents, metals and various chemicals, as well as effluents from septic tanks and waste disposal sites, typically contributes a greater pollution load per unit area than does agricultural runoff.

Runoff from rural areas contains herbicides and pesticides, fertilizer nutrients applied to the soil, nutrients and organic compounds naturally occurring in the soil, decayed leaf and plant residue and wastes from pastured animals and ildiife. In addition, sediment, particularly that produced from eroded topsoil, serves as a transporting agent for pollutants such as nitrogen, phosphorus, organic matter, pesticides and pathoqens. In the study area, agricultural runoff is likely to be the greatest contributor of pollutants to surface waters, primarily because of the greater areal extent and the intensity of cultivation of agricultural lands.

Comprehensive water quality data is available only for Boambee Creek. In the absence of other data it is necessary to assume that this data is typical of water quality in all streams within the study area. It is thought that this is a valid assumption, (1) although variation from stream to stream is expected. The basis of this assumption is that land use and other critical factors determining water quality do not vary substantially from catchment to catchment.

(1) Personal communication with W. Pradhan, S.P.C.C. 10/7/79

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Table 3: Water Quality in Boambee Creek

Position

England' s Pd., N of tip

Pacific H'way (Cordwells Creek)

Lincisays Rd.

Pacific H'way (Newports Creek)

Picnic Point

F.coli 14,000 52 32 28 0

Coliform (per 1 OOml) 22,000 3,200 4,700 4,900 0

Total Colony Count 130,000 7,000 9,000 3,000 21

pH 6.91 6.64 7.45 7.10 8.26

(mg/i) 7 20 6 7 5

Turbidity (Ftu) 18 9 5 8 3

NTI3 -N (mg/i) 1.06 0.01 0.01 0.01 0.01

Aib - N (mg/i) 0.96 0.09 0.04 0.13 0.01

NO3 - N 0.01 0.02 0.10 0.03 0.006

NO2 - N

Phos - P (mg/1) 0.188 0.054 0.067 0.043 0.029

Source; Proposal to Classify the Waters of Boambee Creek Catchrnent Area, S.P.C.C.

In Boambee Creek water quality varies along the streams Jenqth. cenra1iy, pollution problems are minimal in the

lower reaches of the stream and this can be attributed to regular tidal interchange. Similar conditions can be expected to occur in other streams where the river mouth is not blocked by sediment. However, outside tidal reaches there are a number of water quality problems and the stream cannot be considered fit for domestic use, body contact recreation or fish propagation.

The results show that levels of faecal bacteria and Biological Oxygen Demand (BOD) are high. It is also known (2) that high faecal bacteria levels have occurred regularly in Coffs Creek. The presence of faecal coliform organisms fEscherichia coli)in a water sample indicates recent and possibly dangerous pollution from sewerage effluent. BOD is a measure of the amount of oxygen required to remove waste organic matter from water through the process of decomposition by aerobic bacteria and provides an index of the degree of organic pollution of water. The measurements indicate low levels of dissolved oxyqen in the upper reaches of the stream.

Surface runoff and soil erosion from banana plantations are of particular concern. This is because of the steep lands used, the incidence of high intensity rain storms and the quantity and type of chemicals applied to crops. igriculturai chemicals used on banana plantations include the fertilizers nitrogen, phosphorus, potassium, dolomite and lime, the pesticides dieldrin, nemacur and mocap, miscible oil as a fungicide and the heavy metals zinc sulphate and copper. All of these substances are potential pollutants if they are allowed to accumulate in streams. Nitrogen and phosphorus are nutrients that may cause eutrophication of surface waters. Diedidrin is a highly toxic and persistent chemical that is lethal to both fish and mammals in small quantities and the same is true of zinc and copper.

In view of the vulnerability of the coastal streams to pollution and the high demands on them for recreational use, especially fishing and swimming, careful water qualtiy management is warranted. It is therefore thought that the catchrnents of the streams should be managed so as to achieve Class C, Controlled Waters, in the tidal zone and Class P, Protected Waters, above tidal limit.

This would involve imposition of restrictions on the quantity and composition of wastes that may be discharged into creek systems. Unfortunately, this form of management does not

(2) personal communication with Mr. F.B. Smith, Health & Building Inspector, Cotfs Harbour Shire Council.

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cover non-point sources of pollution and, as has been previously suggested, these would be the major source of pollution. For this reason, in addition to the relevant provisions of the Clean ¶aterS Act it is suggested that the following land management practices should be encouraged in existing rural areas:

(a) Practices to control erosion and runoff -

To increase soil infiltration rates encourage agronomic practices that result in dense vegetation cover, abundant mulch or litter, high soil organic matter content, good soil structure and good subsurface drainage.

Employ contour strip cropping and contouring of fields and pastures.

Clear and prepare new plantations in the drier months of the year.

Stabilize channels running from fields by establishing a qrass cover.

Establish detention basins where suitable sites are available on drainage channels leading from intensively used land. Water collected in these ponds should be used for irrigation.

Establish a 50 to 100 metre natural vegetation preservation and reveqetatiOfl zone around major stream channels.

Construct roadways to traverse contours rather than cut across them and ensure that roads are sealed. provide regular outlets for runoff from roadways into gravel filled detention basins overlying well drained soils.

Adopt measures to control erosion from contructiOn sites including minimising site clearance, removal and storage of topsoil, temporary mulching of cleared areas, construction of temporary detention ponds in drainage swaes leading from construction sites and mirnirniSing site distu:bance activities at that time of the year when rainfall is highest.

(b) Nutrient Practices

1. Avoid fertilizer application when there is the likelihood

of heavy rain and runoff potential is high, that is, during February and March, and to a lesser extent during January and April.

Tvoid fertilizer application in places that are poorly drained or where runoff rates are high, that is, within drainage swales or in areas of high water table.

Make small applications of fertilizer more often rather than single, large applications.

L • Locate intensive agricultural activities such as poultry farms and piggerieS outside the catchments of lower order streams. Ensure that effluents from these facilities are to Class O c t Controlled Waters standard and that discharge is into the lower tidal reaches of streams.

(c) pesticide Management Practices

When applying pesticides, place them in narrow bands below the soil surface or directly into seed furrows rather than spreading them over the soil surface.

Encourage the use of pesticides that have a low toxicity, are not persistent and do not build up through the food chain.

5. Flooding

The study area consists of a flat plain backed by steep mountains and over this area severe storms bringing torrential downpours are a regular occurrence. Substantial surface water runoff is generated during these storms and this moves quickly down the steep slopes, spreading over the flat plains below. in addition, the natural rates of surface water runoff have been increased through the activities of man, particularly the clearing of vegetation and construction of impermeable surfaces in land development.

P% characteristic of rivers is that they cannot form a channel that will convey without overflow all possible flow events. In fact, generally the channel can contain within its banks only a discharge of modest size. Greater discharges must overflow into the valley floor within which the channel is located. For this reason the floodplain is in fact part of

the channel during major storm events. When man uses this part of the valley for urban purposes, he is encroaching on the river and the structures located there may be damaged or destroyed when overflow occurs.

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within the study area the catchrnent areas of coastal streams are not large and therefore flooding is not a severe problem in that the duration of flood events is likely to be relatively short. Much of the flooding that does occur is in the form of localised surface water inundation in poorly drained locations. Despite the lack of severity, flooding that does occur is a significant constraint to development. This is because of the direct damage to buildings and the indirect damage caused by poor foundations where major fluctuation in the height of the water table occurs. In addition, there are the costs of drainage and filling necessary to overcome these problems and with this the destruction of environments that are often valuable habitat for water birds.

ccurate mapping (3) of flood prone lands has been difficult to achieve because of the lack of settlement in many areas and the absence of hydrologic data for streams except Coffs and ooiqoolga Creeks. The method employed has been to use historical information provided by lonq standing residents and to detect regular inundation from soils and vegetation data. Thus where soils were found to have a water table within 600mm of natural surface level and where the soil profile showed evidence of a consistently high water table and also where the vegetation in the same area was dominated by species known to depend upon periodic inundation, these areas were designated as flood prone.

This analysis showed that substantial areas in the north and south of the study area are subject to flooding. The largest area is that stretching from Red Rock through to Arrawarra, generally to the east of the Pacific Highway. Aside from elevated land in the vicinity of Corindi Beach almost all of this natutally poorly drained area appears to be subject to regular inundation.

Cther areas of major flood hazard are the low lying lands surrounding the coastal reaches of Boambee, Pine and Bonville Creeks. Less extensive areas also appear to be flood prone around Moonee Creek.

The remainder of the study area appears to be relatively free of flood problems. This is because well elevated, undulating land reaches the coastiin. However, even in these locations a narrow flood plain is present at the base of all valleys.

(3) The >ception is Coffs Creek where a 1 in 100 year flood plain has been identified by the Department of Public works and Laurie, Montgomerie & Pettit Pty. Ltd.

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YEAR F' 'PO PLAINflL' 'MG

HOU PFWVKMLY

LEVEL

EFFECT OF FILLING APPROX 501 OF CROSS SECTIONAL AREA OF FLOOD PlAIN

FLOOD NGE

REGULATORY FLOOD LEVEL

EXAMPLE OF FLOOD PLAIN ZONING USING A FLOOD FRINGE DISTRICT

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B. GROUNDWATER HYDROLOGY

1. Gtoundwater Quantity

Groundwater bearing potential is extremely variable, being dependent upon geology, elevation and slope of the bore site, the amount and distribution of rainfall, vegetation coverage and the permeability of the overlying soil type. Generally, supplies from bedrock are relatively small. Much of the study area is steeply sloping and it is therefore assumed that groundwater recharge in these areas would be low. As well as this, the bedrock is mostly impermeable, offering only secondary openings in the form of fractures, cracks, joints and partings. The most significant groundwater resources come from the Quaternary sediments.

During the winter months irrigation water is applied to bananas and other crops unless rain falls. Because of this need to irrigate many crops in winter, groundwater resources are potentially a valuable support' to the agricultural industry. in addition, groundwater can be used to supplement town water supplies or as the water source for semi-rural estates and thus may help to overcome the imposition of water restrictions in summer.

(a) Groundwater from

Quaternary unconsolidated marine sand and aeolian deposits and alluvial gravel, sand, silt and clay beds have the most potential for supply of substantial quantities of water. Coastal sand deposits are capable of yielding more than 5 litres per second while the numerous bores on the alluvial flats yield between 0.2 to 1.9 litres per second.

Sithin the study area there are fairly extensive areas of marine sand and aeolian deposits, particularly in the area running from Bundagaree ileadland to Sawtell and behind Boambee Beach. The thickness of these deposits varies, exceeding fifteen metres in large dunal areas south of Sawtell but being less than three metres in the northern parts of the study area.

The water in storage in the southern coastal areas, assuming an average saturated thickness of ten metres, would be 5•4 x

lO litres per square kilometre, with the available yield per square kilometre being in the order of 5.0 x 106 litres per

annum.

This water has accumulated mainly through direct infiltration of rainfall. Minor contributions have come from infiltration of surface water runoff and direct recharge from coastal streams.

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(b) Groundwater from Bedrock Geolo

The Brookiana Formation, which is composed of mostly massive argillites, can be regarded as not being a potential source of groundwater. The Coramba Beds are known to contain some saturated strata. However, the rock is generally massive and groundwater supplies are expected to be negligible.

Contrasting with this the Narnbucca Phyilites are a formation that contains many old bedding planes and fractures and has been deeply weathered. Fault zones within this unit are likely to provide useful quantities of groundwater and thus in the Bonville area around the Crossmaqlen Fault groundwater supplies should be significant. The total salinity of water from these strata is expected to be in the order of 1000 milligrams per litre.

2. GROUNDWATER QUALITY

salt levels in qroundwaters vary from 70 to 870 milligrams per litre in dunal locations and from 75 to 200 milligrams per litre in alluvial locations. These quantities are thought to be acceptable for both domestic and agricultural use. However, salt water incursion into groundwater has been recorded in the Woolgoolqa area. Thus care should be exercised in limiting the rate at which water is taken from groundwater, especially in locations close to the ocean or estuaries.

part from measurements of salt content, no empirical data on groundwater quality exists. Howevr, it is possible to make some qeneraliSatiOnS. It is known that the leachate from waste disposal sites, effluents from septic tanks and agricultural. fertilizers and pesticides are the major causes of groundwater pollution in locations outside metropolitan

areas. These materials are leached through the soil as groundwater is recharged.

It is also known that soils have a varying ability to retain these materials. where there is a high organic matter or clay content, the cation exchange capacity of the soil particles is likely to be .;ufficient to retain pesticides, organic wastes and toxic inorqanic compounds especially if the soil has a

high pH. This property is enhanced where the soil body is deep, has a high elevation above the water table, drains at a moderate rate, is flood free and is located on flat to undulating soils, -

soil to the he

.groundwater-j and land. Elsewhere, in more inert, rapidly draining or shallow soils, pollutants leach through the soil to the qroundwrit'r and later appear as concentrations in

surface waters. This hazard is also present in areas where the water table is close to the surface.

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OF EF!UNT SPRING POLLUTED MY WtU POLLUTED MY UNDERGROUND SEEPAGE TQI FROM SEPTIC TANK. CONThMM4AIW GROIJNO SPRING POLLUTES STREAM. .'MTER THROUGH AQUIFER.

WELL DRAINED

DRAI

SECTION TO SH(IW THE ORIGIN OF POLLUTK)N OF WELLS AND S4mICE WATER FROM SEPTIC TANI(S OR SEWER LEAKAGE ON WELL DRAWEX) SOIL

On this basis, within the study area where residential areas using septic tanks or rubbish tips are located on sandy soils or poorly drained alluvial soils, groundwater bodies are

likely to contain excessive nutrient levels and possibly pathogenic bacteria. Thi.s would make these water supplies unfit for domestic use and could possibly lead to eutrophication of surrounding surface waters.

. SITE SELECTION FOR SEPTIC TANK

As has been previously indicated many soils are unsuitable for septic tank usage. Failure of septic tanks takes three forms:

Hydraulic failure where a soil cannot absorb the waste water flowing into it and thus either overflows in the house or comes to the ground's surface in the area surrounding the septic tank.

Delivering excessive numbers of potentially pathogenic bacteria and viruses to water bodies.

(C) Causing increased nitrogen arid phosphorus inputs in ground and surface water bodies, which may in turn enhance eutrophication of surface water of cause potentially toxic nitrate levels in town water siipplies.

However, a properly operating soil absorption field can treat and nearly completelv purify septic tank effluent. The soil can be very effective in removing Bio1qiCal Oxygen Demand (BOO) , phosphorus, pathogenic bacteria and viruses.

It is therefore considered that tjje fo1loiinq standards should be adopted in selecting sites suitable for on site sewerage disposal:

Nrcolation rate: less than 25 minutes for 2.5 centimetres fall in water level, from a hole 1 metre

deep.

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Bedrock: at least 90 centimetres of soil over bedrock on 80% of lot area and 180 centimetres of soil over bedrock on the remaining 20%.

Slope: over 80% of the site being no greater than 12% slope.

Groundwater: highest estimated level of the water table at least 100 centimetres below the bottom of the absorption trenches.

Flooding: sites must not be subject to flooding, 90% of the lot area must be at least 70 centimetres above flood elevation.

Absorption Capacity: cation exchange capacity greater than 10 m.e. per 100 grams, preferably with a high pH value.

in addition, it should also be realised that septic tanks cannot be considered to be a viable long-term solution to sewage disposal. Even on well suited soils disposal of effluent causes clogging of soil pores, resulting in a gradual reduction in permeability and a loss in assimilative capacity. For this reason residential lots using septic tanks should be large enough to permit installation of a parallel and a second system after a certain period of time. Where the conditions set out above are met a settlement density of approximately 6 persons per hectare is possible.

L • SITE SELECTION FOR WASTE DISPOSAL

The objective is to utilize sites that will not allow leachate to enter ground or surface water in a polluted state. Sites suitable for this purpose are flat, well elevated above the water table and are removed from wetlands and surface waters, In addition, soils should be predominatly deep clays, preferably with a low shrink-swell characteristic. Thus, abandoned brick clay quarries or clay deposits underlain by bedrock are likely to be the most suitable sites.

IO ROCK

,-

j WOOLGOOLGA

/ J

/

MA P 3

I

) GROUNDWATER

BEARING POTENTIAL

'4 GH

/ [IlI• S UTNES I SECORO

SSNTELL EI3II 02-19 LPTRESI SECOND

[J11 SGNIIEANT CKJANTITIES

LOWE_Ill

Jr 9

+ 4 4 4 4•4-

4

Sck 0 2 4 6 0km

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REFERENCES

Beatty M.T. and Bouma J. APPLICATION OF SOIL SURVEYS TO SELECTION OF SITES FOR ON SITE DISPOSAL OF LIQUID HOUSEHOLD WASTES, Geoderma, 10, 1973.

Brady, N.C. THE NATURE AND PROPERTY OF SOILS, MacMillan publishing Company, 1974L

Center for Ecological Research in Planning and Design, University of PennsyVaflia, MEDFORD, 1974.

4 Communication between Water Resources Commission and Miss D. Madden, Planning and Environment CommissiOn, 23rd December, 1977.

Leopold L. WATER, W.H. Freeman & Co., 1974.

Laurie, Montgomerie and Pettit Pty. Ltd., REPORT ON COFFS CREEK FLOOD INVESTIGATION, 1978.

Personal Communication with Mr. G. Mounser, Department of Public Works, Coffs Harbour.

Personal Communication with Dr A. Johnson, Department of Landscape Architecture and Regional Planning University of Pennsylvania, 26/6/79.

Personal Communication with Dr D. Turner, Aistonville Tropical Fruit Research Station, Department of Agriculture.

lo. Personal Communication with Mr N. Hamey, Sawtell.

Personal Communication with Mr R. Hicks, Soil Conservation Service, 26/7/79.

Ringis, J. UNDERGROUND WATER IN COASTAL SANDS RED ROCK - COFFS HARBOUR, The Geological Survey of New South Wales, 1965.

Soil Conservation Service, URBAN EROSION AND SEDIMENT CONTROL, 1978.

Personal Communication with Mr W. Pradhan, State Pollution Control Commission, Armidale.

University of Delaware Water Resources Centre, WATER RESOURCES PROTECTION MEASURES IN LAND DEVELOP14ENT - A HANDBOOK, U.S. Department of the Interior, 1974.

U.S. Environment Protection Agency, CONTROL OF WATER POLLUTION FROM CROPLJ\Nfl, 1975.

U.S. Environment Protection Agency, THE BENEFICIAL USE OF STORMWATER, 1973.

U.S. Environmental Protection Agency, STREPM QUALITY PRESERVATT ON THROUGH PLANNED URBAN DEVELOPMENT, 1973.

U.S. (eolOgical Surv(n.y, A PRIMER ON WATER QUALITY, 1965.

I) Wct (;,ve rfl pefli Pifl te C. New Sut h Wales I 9 ll()