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INFORMATION Received 200913 ~1 DEPARTMENT OF INFRASTRUCTURE PLAN!!tiQ pl)q 'WILDING r.ONTROL ~C -'1jIl~N 1tJWn and Countrv PI-?n.,in:"1 ,:,:;;. -'<')99 o SEP 20~3 .' ';"",-',"":' Mallards, Santon Proposed Botanic Gardens Hydrology Planning Statement ~~9SeP13 - 1709 - Private Dwelling, Santon - Estate Masterplan ~ BURROUGHS STEWART ASSOCIATES M
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1709 INFORMATION Mallards, Santon Proposed Botanic Gardens Hydrology Planning Statement 18/09113 Alistair Burroughs Piers Burroughs --1 ;9SeP13 ~ BURROUGHS STEWART ASSOCIATES M
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'109. I'f" ••• o...Jir"'l,sar-
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, lOR I'n¥a ~ S;inolo\ - h •• l ••••.• l","~~",,,~ 6.0 PA 13/00833/8: Garden: Area C 6.1 Hydrology 62 Construction 63 Operatlon 6.4 Default 7.0 Conclusion Appendices ~ BURROUGHS STEWART ASSOCIATES ~ Creation of Gardener's Compound and Sensory Appendix A Mallards, Botanical Gardens: Areas of the Planning Applications
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l/W 1'n'0IIl~5.orJlDI
E••• ",_P'oof1
I••...,~
_~l!Ql;R:
~
Planning Applications
~
BURROUGHS
STEWART
ASSOCIATES
~
PA 13/00830/8:
Creation of Production
House and Walled Garden: Area E
PA 13/00831/8:
Creation of Water Cascade and Amphitheatre:
Area 0
PA 13/00832/8:
Creation of Meadow, Orchard, Lake, Wetlands,
Boglands and Glen: Area
B
PA 13/00833/8:
Creation of Gardener's
Compound
and Sensory Garden: Area C
Hydrology Planning Statement
CA R.D IFF
UNIVERSITY
The Hydro-environmental
Research
Centre at Cardiff University,
School of Engineering,
led by Professor
Falconer FREng has provided preliminary
expert hydrology assessment
and input and are happy to provide lead hydrology expertise for this project.
The Hydro-
environmental
Research
Centre
has an international
reputation
in environmental
water
management.
with collaborative
work being undertaken
in over 19 countries,
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Ii'O'lPol_ D-.g StMo" htao lol_pl'" T.••",_-~G;w 1.0 Introduction ~ BURROUGHS STEWART ASSOCIATES ~ Mallards Botanical Garden is an Estate with associated buildings thai will contribute significantly to the Island's heritage and create a Botanical Garden of global standing and worthy recognition. This supplementary Statement is in support of the above Planning Applications: it has been prepared to review the approach to the design issues for the management of hydrology that will evolve, but have yet to be established, to demonstrate a recognition of the issues and how they will be managed, as part of the design development process in advance of construction should planning approval be given. The areas of the application are diverse in nature and intent, the issues are different, and where they are different they have been dealt with separately. The overriding intent is to achieve the vision without adversely impacting upon the existing hydrology; this is not to say that there will be no impact, as consideration will be given to the management of existing natural flows, ensuring that at times of low flow, existing flows are maintained and that where sensible with river flows in spate, the forward flows are managed to help minimise the adverse impact of a storm. However, the basic criteria that shall be deployed throughout the design and construction process will be to manage the flows through development to achieve the concept but to maintain the status quo. It is considered that several elements of the proposed works will fall under the existing Land Drainage Regulations, so the approach, modelling and calculations will form part of a package that will be submitted to the Water and Sewerage Authority for approval. t'ilIlO 1III I,
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1109Pl-.•• ~ s..--E.-~ ''''''''_ I~",-,Io_c:.._ ~ BURROUGHS STEWART ASSOCIATES ~ 2.0 Scope of the Works to the Existing and Proposed Water Courses 2.1 The Riverthat FlowsthroughArea B, Existing This is an existing river that passes through Area B. It is not proposed that the course of the river will be altered either during or after the works. 2.2 The StreamalongsideBallavaleRoad and through the Ashdowne House Estate, Existing This too is an existing stream. It presently receives surface water from Ballavale Road, water off the railway and from the bottom of the valley; it is not proposed that the course of this stream will be altered either during or after the works. 2.3 The Cascade,Poolsand Pond,Proposed This is a proposed self contained feature which, in addition to being a visual amenity, will be used to naturally aerate the water to outdoor and indoor pond and swimming poo1. 2.4 The Springand StreamaroundAshdowneHouse,Existing This is an existing stream which will be retrained to pass through the lake and wetlands to be returned to the river that passes through Area B down stream of its present connection point. In order to maintain the flow, natural aeration and visual appearance, a recirculation system will be incorporated for times of low flow with borehole water being used to supplement low flows at times of drought conditions. The use of boreholes is subject to testing.
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111J9P'"iIlOD-..g SOiIbn- E.talel,lamrpi •• I MeMoIl.a. - ",,,,,&.oocI tIatan<; G.",,", ~ BURROUGHS STEWART ASSOCIATES ~ 3.0 PA 13/00830/8: Creation of Production House and Walled Garden: Area E 3.1 Hydrology It is nol anticipated that the creation of the Production House and Walled Garden will present any unmanageable or unusual issues that will adversely impact on the existing hydrology. The creation of this aspect of the Gardens will result in a rescaping of the existing topography to a small degree. perhaps revealing the water table; management of the water table, if required, will be through a system of land drains. The land drains will facilitate the suppression of the water table below the Production House, but will facilitate reintegration of ground water and potentially irrigation of the Gardens. 3.2 Construction It is not expected that any construction activity will impact adversely on existing surface or ground water flows. The area is small; rainwater collected on the surface will be directed around the areas of activity towards the nearest catchment oriented field ditch. Care will be taken to temporarily retain flows so that they are maintained at the same rate as green field runoff and to ensure that the possibility of pollution is avoided. In order to freely create the Gardens, the level of ground water will be proven through site investigation and monitored through the seasons for change. Should it be encountered, the first stages of work will be to introduce the land drainage system, providing the design control on flows and also providing a workable site. Construction activity will be controlled to stay within the expected limits of farming activity and whilst there will be noise associated with the excavation activities, it will be similar to tractors harvesting and for a limited period. It is not expected that bulk soil movement will exceed three months, with the total construction period of circa nine months. During long dry periods of the summer, dust will be controlled by dousing. 3.3 Operation The operation of the land drainage system will be by gravity, with little maintenance required. The design will be such as to facilitate water movement and flow with little transfer of fine soil fragments. Access points will be provided. It is not anticipated that the rescaping and the replanting of the land will to any degree impact upon the existing surface water runoff, with the impact expected to be nominal. Rainwater off the roof of the Production House will be harvested and used for irrigation, with the water held in underground tanks until required. Pumping equipment is thought to be required to sensibly transfer the harvested water, but this will generally be operated by hand as demand requires. l'ajeJoll}
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1M f'n,,,,,, O-..g. S"'1O'1- l$la!<l'-'-pIaII l!W'l.l""wa,~IIot_l;;" 3.4 Defaul! ~ BURROUGHS STEWART ASSOCIATES ~ If in the unlikely event the works installed were left uncared for, apart from uncontrolled and overgrown planting areas, it is not envisaged that there would be any major degradation of the land drainage system, as water will always follow the least line of resistance, the land drain. The rainwater harvesting tank will be fitted with an overflow linked to the existing land drainage system, so that in the event it were not used, water would continue to flow to and within existing land drainage ditches. A control wilt also be fitted, so that when used, it would limit the discharge to be equivalent to the green field run off rate
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,rot1'1'''0-.,. ~ t.u.~ '''~O$ ~_~ ~ BURROUGHS STEWART ASSOCIATES ~ 4.0 PA 13/00831/8: Creation of Water Cascade and Amphitheatre: Area 0 4.1 Hydrology It is not anticipated that the creation of the Water Cascade and Amphitheatre will present any unmanageable or unusual issues that will adversely impact on the existing hydrology. These mo elements, the Amphitheatre and Water Cascade, are mo entirely separate elements that form Area D. The Amphitheatre is proposed to be constructed within an area that naturally lends to the shape of the terrace required and whilst there will be a need for some rescaping of the land and the formation of the terrace, it is not anticipated that any excavation will impact upon the existing ground water table. As the shape tends to the existing, management of surface water flows, storm water, will be guided across the soft grass terrace surface to discharge within ditches within the same catchment boundaries to follow the same point of outfall as now. The Water Cascade, on the other hand, is a man made closed circuit feature, created within the landscape to facilitate the natural aeration of the water, to serve the naturally filtered extemal pond and indoor swimming pool. It is not anticipated, other than perhaps initially, that it will be fed naturally; it will be a circulating system, so that the same water is lifted from the pool and circulated to the top of the Cascade, water flowing through the hillside until it is filtered again and used to replenish the pond and swimming pool. The creation of the series of ponds and rivulets that form the Cascade will be shallow, formed predominantly within one metre of the surface and potentially be lined to manage water losses. The external pond and internal swimming pool, fed by the cascade, will be deeper to facilitate swimming, circa 2m deep. It is not expected that there will be any external (to the Cascade system) water supplies other than surface water, through storm I rainfall. Rainwater, where it might exceed the capacity of the system, wilt be passed through overflows into the existing land drainage nemork. 4.2 Construction It is not expected that any construction activity will impact adversely on existing surface or ground water flows, The area is small and rainwater collected on the surface will be directed around the areas of activity towards the nearest catchment oriented field ditch, Care will be taken to temporarily retain flows so that they are maintained at the same rate as green field runoff. In order to freely create the Amphitheatre and Cascade, the level of ground water will be proven through site investigation and monitored through the seasons for change. Should the water table be encountered, the first stage of work would be to introduce the land drainage system, providing the design control on flows and also providing a workable site. If necessary, the design of the Cascade will be adjusted to minimise the impact with the water table. The underside of the external pond and internal swimming pool may reach the water table, the impact of which will largely be experienced during construction and land drains will be used to temporarily divert the flows. Upon completion, both Pond and Swimming Pool will be lined, to prevent leakage and to prevent them from impacting on the water table. There will be noise associated with the excavation activities for the theatre and pumping stations, but these will be similar to tractors harvesting, for a limited period, and will not extend beyond the normal farming day. It is expected that the construction of the
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11011 ""_~s..- f _ 1". •••••• IlI-Pro;!.. __ ~ ~ BURROUGHS STEWART ASSOCIATES ~ Cascade will be "by hand" and with a "mini digger" as care is taken in formulating the ponds and rivulets. There wilt be excavation and reinforced concrete works associated with the construction of the pump stations and storage tanks for the Cascade. the pond and the swimming pool. Total construction period will be within nine to twelve months with bulk soil movements unlikely to exceed four months. It is not anticipated that dust will be a major issue, but should it become so during long dry periods of the summer, dust will be controlled by dousing, 4.3 Operation The creation of the Amphitheatre will not significantly impact on the existing hydrology, with surface water flows maintained as existing. The creation of the Cascade will impact upon existing catchment flows, however, only within the environment of Mallards and only for surface water, rainwater. As the system is self-contained apart from nominal losses, additional rainwater arriving will be unwanted and hence will be returned by gravity through gravity over flows into the existing catchment land drainage system. So effectively, after a short period, there will be no impact on existing natural flows as they leave the site. It is not anticipated that the rescaping of the land will to any degree impact upon the existing surface water runoff. The successful operation of the Cascade is dependent upon a suitable pumping regime, and therefore dependent upon mechanical elements. There are several issues that the design will consider: .;. Reliability of power: Stand by generation; -~. Reliability of pumps: Stand by pumps; ,j, Noise and vibration: Suppression and screening of vibration and noise, ensuring that mechanical plant is working within sensible limits and not at capacity; ~ Plant failure: Provide an underground tank to retain the capacity of the Cascade, so that it does not need to discharge in an uncontrolled way to the land drainage network. The visual impression of the Gardens is part of the vision; where plant rooms are required they will be created underground. 4.4 Default If in the unlikely event the works installed were left uncared for, apart from uncontrolled and overgrown planting areas, it is not envisaged that there would be any major degradation of the land drainage system. Clearly, the Cascade would stop, but the rainwater collected would continue to follow the least line of resistance and flow along the channel, through the overflow, into the land drainage network. The proposed changes to the landscape are nominal; as already nOled, the creation of the Water Cascade is within shallow depth. Reinstating the catchment, should it be required, would be easily and simply achievable.
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1/09 1'n•• Dw.ilnl••••••••fWll!~ 1•• ...-41; 1'roI.' """""," ~_11 BURROUGHS STEWART ASSOCIATES The external pond would continue to receive rain water, which would arrive at and therefore overflow at the green field run off rate, so would not adversely impact upon the surrounding catchments. With the cascade not working, it is expected that the pond would mature, although during drought periods could dry out.
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