RESTORATION OF WATER FEATURES AT BRAMHAM PARK: A HYDROLOGICAL FEASIBILITY STUDY. Part III

Transcription

1 RESTORATION OF WATER FEATURES AT BRAMHAM PARK: A HYDROLOGICAL FEASIBILITY STUDY Part III Operation of the water features, water availability and potential for restoration Research on behalf of English Heritage and the Bramham Estate conducted by: Joseph Holden and Andy Howard 30 th June 2003 School of Geography, University of Leeds, Leeds, LS2 9JT Contact: Dr Joseph Holden j.holden@geog.leeds.ac.uk Tel: (Direct) Tel: (Reception) Fax: i

2 CONTENTS Chapter Title Page No. I Contents ii II List of Figures iv 1. Executive summary 1 2. Introduction Background Reminder of the brief Aims and scope of this report 6 3. Methodology and monitoring locations Monitoring instruments Water level recorders Air pressure recorder Rain gauge Data calibration and analysis Other data sources General hydrological audit of the Estate Results of hydrological monitoring Combining hydrological results with archaeological 24 data and water needs 5.1 Sites in need of complete restoration Water needs of features Queen s Hollow and Parterre cascade Obelisk pond cascades Obelisk pond sub-tropical garden Obelisk Fountain Water supply, water needs and climate change Implications of results and main options for restoration Option Option Alternative strategies to allow full restoration Alternative water sources for the gardens Phases of restoration Site survey and proposals Introduction Whittle Carr Jenny Sober plantation JS 3 to confluence JS 4 to confluence Confluence to intake pipe Southern Parkland (or Rough Pasture) The Garden The T Pond 54 ii

3 6.5.2 Queen s Hollow and Parterre cascade The sediment trap at Gothic Temple Obelisk ponds and cascades Cascade Valley Cascade Valley to Bramham Beck Bramham Beck, Lendrick Hills and Terry Lugg Farm Black Fen Other issues Value added References 88 iii

4 LIST OF FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Conceptual model of the main components of the Bramham Park water features to be assessed. Dashed lines indicate features currently not operating. Location of hydrological instruments installed at Bramham Park The DIVER pressure transducer. Some monitoring sites Tipping bucket rain gauge Connectivity of gauging sites. Amount of water in 1000s of cubic metres that flowed through the measurement points between 1/8/02 and 31/12/02 with proportional circles. Monthly discharge totals from the gauging sites Figure 9 15-minute discharge for all sites from 15/7/02 to 18/3/03. Figure 10 Figure minute discharge at the sampling points Daily gain in discharge between the Whittle Carr spring and the T Pond input Figure 12 Daily gain or loss in discharge between the two Jenny Sober springs and site 5 Figure 13 Daily gain or loss in discharge between site 5 and site 6 Figure 14 Figure 15 Figure 16 Leak from side of intake pipe at site 5 in the Jenny Sober plantation Water seeping and dripping into the Jenny Sober supply ditches through the rock Pond downstream of Whittle Carr Grotto with arrows indicating slopes that feed water into the pond that then goes on to supply the T Pond Figure 17 Sum of discharge at site 2 and site 5 15/7/02 18/3/02 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Queen s Hollow and Parterre Obelisk Pond cascades Sunken side pond on the northwest of main Obelisk Pond. Plan of features in the Garden Mean monthly (a), seasonal (b) and annual rainfall totals at Bramham Figure 23 Precipitation changes in percent, from the UKCIP (Hulme and Jenkins, 1998). Figure 24 Bramham Park Character Areas (From Landscape Agency, 2001) iv

5 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Figure 36 Figure 37 Figure 38 Figure 39 Figure 40 Figure 41 Figure 42 Figure 43 Figure 44 Figure 45 Figure 46 Figure 47 Figure 48 Figure 49 Whittle Carr and Jenny Sober water supply features Whittle Carr Spring water Photographs of the Whittle Carr Grotto Whittle Carr Pond Rainwater storage tank Raised banks around JS3 with bankside trees JS 4 flow Sketch map of the Jenny Sober ditch from the confluence of the two spring channels to the intake pipe. Jenny Sober ditch Rough Pasture natural drainage lines 1987 OS map of the Rough Pasture Piping across the Rough Pasture Stopcock and outlet to Rough Pasture The site of the Rough Pasture reservoir Leak from T Pond into Rough Pasture T pond neck T Pond head Piping from the T Pond head Features of the Queen s Hollow-Parterre system Water route towards the Obelisk Ponds and the sediment filter Sediment trap features Outfall near the Gothic temple upstream of the Half Moon Pond Supply to the Half Moon Pond Dry Obelisk pond and archaeological exposure of the Obelisk Pond cascades during Sediment filter at main Obelisk Pond leading to Cascade Valley. v

6 Figure 50 Figure 51 Figure 52 Figure 53 Figure 54 Figure 55 Figure 56 Figure 57 Figure 58 Figure 59. Figure 60 Figure 61 Figure 62 Figure 63 Figure 64 Drainage system around the edge of the main Obelisk Pond. Algae on the surface of the Obelisk Pond. Pipe from the lowest southern Obelisk Pond to the stone bridge at the end of Cascade Valley Three ponds in Cascade Valley shown on the c.1728 map of Bramham drawn by John Wood the Elder Remains of the pool at the foot of the Obelisk Pond cascades Stone conduit emerging from embankment across Cascade Valley Map of the water course from the Obelisk Ponds to Bramham Beck Valley immediately below Cascade Valley Cattle drinking trough and intake system with broken grate Open water towards Bramham Beck from the Obelisk Ponds Bramham Beck immediately upstream of the Estate boundary Thorner Road bridge Bramham Beck in the Lendrick Hills with numbered sites discussed below Stone bridge over Bramham Beck Overgrown track along Bramham Beck Figure 65 Fish Pond 1 Figure 66 Fish Pond 2 Figure 67 Figure 68 Figure 69 Figure 70 Figure 71 Figure 72 Figure 73 Site of wooden bridge adjacent to fish pond weir Stone arch bridge Disused pump openings to be covered over Ponding and meandering tributary flow across valley floor with aquatic vegetation. Stone bridge with damaged top stones Black Fen open watercourses Water courses in Black Fen vi

7 1. Executive Summary Geocat based in the School of Geography, University of Leeds was commissioned to prepare a feasibility study of the hydrological restoration of late 17 th and early 18 th century water features at Bramham Park, West Yorkshire. This report is the last of three reports prepared to achieve a brief provided by English Heritage on behalf of the Bramham Estate. The first report detailed the findings from a geophysical survey aimed at determining the original connectivity and operation of water features in the grounds (Holden et al., 2002). The second report served two purposes; i) to describe the interim results of a one year monitoring exercise on the groundwater springs that supply water through the gardens and ii) to provide a draft final report for comment. This present third and final report contains responses to those comments and full analysis of the complete discharge record. The discharge monitoring was designed so that leakages or water inputs between water flow sites could be established. Results from discharge monitoring are then used in combination with the geophysical results to allow a range of restoration options to be explored. Specific recommendations are made on the options for reinstating the abandoned water features and the maintenance and repair of present flowpaths. Full restoration to the original garden design powered by gravity and determined by spring water availability will not be feasible. However, partial restoration through this method would be feasible. Full restoration would only be possible through additional use of more modern techniques (e.g. pumps) which would supplement a gravity driven spring-fed system. Conservation and repair are the first objectives, however, and the T Pond repairs are central to conservation of the system. The T Pond leak is a twofold problem. The supply pipe to the pond is leaking, but the clay lining in the pond has broken down and also leaks. In addition, this report provides a summary of research on the wider hydrological status of the historic landscape of Bramham Park and on the sustainability of restoration options. As with any catchment hydrology project it was necessary to adopt a wide range of field techniques across the park over a long period of time in order to determine the range of hydrological processes and conditions that occur on site and to therefore adequately inform management decisions. 1

8 2. Introduction 2.1 Background Bramham Park is perhaps the only large-scale formal garden in the UK to survive virtually unchanged from the early 18 th century, and is probably the largest formal garden left in England. The Park incorporates numerous garden buildings, follies and structures and a range of formal water features. Water was a central feature of many such landscape gardens of the time (Hunt, 1964; English, 1990; Bettey, 1993, Beckett, 2000). A landscape management and conservation plan for the Park was produced by the Landscape Agency during and part of this study identified the need for a thorough investigation into the operation of the water features and the amount of water available to supply them. Some of the water features now no longer operate and others only partially function in the way they appear to have been originally designed. This project aims to assess the feasibility of restoring these water features as part of a hydrological study of the Park. The Park, situated five miles south of Wetherby, is a Grade I landscape dating from the late 17 th and early 18 th centuries, and was laid out by Robert Benson, the first Lord Bingley. The engineered water features include a 30 step cascade, a formal canal (known as the T Pond), a series of ponds known as the Obelisk Ponds and a further sequence of cascades. Although some of the water features still function, many are no longer working, or are only partially operating. Archaeological work has revealed several ponds and cascades that have fallen into disuse (York Archaeological Trust, 1991). The long-term management aims are to restore as many of the water features as possible. However, there is some documentary evidence (e.g. maps; Landscape Agency, 2001) that suggests that some of the water features never actually worked well and may have fallen into to disuse within a few years of construction. Research was therefore needed in order to determine whether restoration will be possible (given water availability) and to determine to what extent work is needed on those features that are currently operating. Thus, there are four main areas for which research was required: i) Calculation of a water-needs budget for the artificial water features, with minimum and maximum levels of flow desirable (i.e. an evaluation of how much water the features require to function adequately). ii) iii) iv) Calculation of a seasonally distributed water availability budget for the water features. Development of an understanding of how the original water features were connected to their water supply and of the potential outlets from these features. Recommendations for the restoration of leaking and non-functioning features and for the maintenance of other parts of the system. There are three key approaches to the hydrological research: i) Monitoring the contemporary hydrological budget. In order to restore the water features it must be demonstrated that there is enough water available in the catchment to supply them in a sustainable manner. Water from springs was historically channelled by gravity via a network of contoured ditches (leats) and pipes to supply the gardens. The main obstacle was a natural valley located between the springs and the ponds. Thus, the channels had to be designed so that gravity would transfer the water around the edges of the valley. The research therefore involved continuously monitoring discharge at the outlets of 2

9 supply springs and also at the input locations to the water feature systems in the Park. This allowed determination of responses of the channels to rainfall events of different magnitude and duration. Water availability and leakage information was then used to inform management decisions. Field surveys of the hydrological conditions of the ponds and conduits were also undertaken. Use of topographic maps, tracing of spring sources and field survey allowed an assessment of the general hydrological status of the site to be made along with recommendations for improvements. ii) Non-invasive geophysical sensing of subsurface archaeological features One of the problems at Bramham is that there are no existing records of how some of the water features originally operated or were supplied with water. A severe house fire in 1828 is believed to have destroyed many of the archives. An important component to the research was to determine how cascades and pond features were connected and drained. It is believed that there are a number of connecting subsurface channels throughout the Park, but in many cases their location was unknown. Attempting to determine the historic connections for water flow between the water features was done through the use of non-invasive geophysical techniques. Principally this involved ground penetrating radar which has been used successfully by the University of Leeds to detect subsurface pipes and leaks and results were presented in the first Geocat report (Holden et al., 2002). iii) Sustainability of management options Of great importance is the need for sustainable management of water within the Park. Research here must take into account three aspects: (i) Potential catchment-scale impacts of management practices;(ii) the need for restoration to be done, where possible, within the original landscape design of the garden and (iii) predicted climate changes that would alter water supply. 2.2 Reminder of the brief: Figure 1 provides a conceptual model of the major components of interest. These have been labelled A to N for clarity. The diagram shows the water features that presently operate and those that are dry. Figure 1 and the questions raised in the 12 point list below (Table 1) were drawn up by Dr Joseph Holden (Geocat) on behalf of English Heritage in response to landscape conservation and management plan recommendations for Bramham Park produced by the Landscape Agency (2001). The research aims to address the following questions (with reference to Figure 1) with text in blue indicating those questions that were dealt with in the first report (Holden et al., 2002). 3

10 Figure 1. Conceptual model of the main components of the Bramham Park water features to be assessed. Dashed lines indicate features currently not operating Bramham Beck F Queens Hollow and Parterre with cascades Historic output? G E Source for historic input? Was the T pond connected to Parterre? K Historic output? L Present output N Cascade valley Dry J Dry side pond Obelisk ponds I Input cascades M B T pond Contemporary output? D Input Leakage C Leakage? Leakage? A Yield Whittle Carr spring H Yield Jenny Sober springs 4

11 Table 1. List of questions and statements from the project brief 1. What is the yield of A (Whittle Carr spring) and what is the mean discharge and its variability through time to B (T pond)? Is there leakage between A and B? If there is leakage the report will need to quantify this and indicate how and where is it occurring? The report should make some proposals as to how any problems can be rectified. 2. Why is the T pond (B) currently leaking (C) and what are the best options for restoration? 3. Where does the water from B runoff to supply (D) and what affects would there be if the discharge through this pathway increased (e.g. through sealing the leak to C) or decreased (e.g. through re-routing water through E to F). 4. What was the historic source of water for F (Parterre cascade). The conceptual model (Figure 1) indicates that this may have been B, but some work will need to be done to test this hypothesis. Geophysical remote sensing may need to be used for this component (e.g. GPR) or another appropriate techniques should be utilised. 5. What was the output pathway (G) discharging from F. Research must establish how to feasibly remove water from F if the feature is to be re-introduced. 6. What would be the best way of supplying water to F and is there enough water available from springs or other sources to allow the feature to feasibly operate. In order to answer this question work will need to establish how much water F requires to operate satisfactorily. A small flow over a cascade would look visually inadequate and would not be in-keeping with the intention of the water feature within the landscape. 7. What is the mean and the nature of variability over time of discharge from H into I and is there any leakage between H and I? If there is leakage some thought needs to be given to best and sustainable management of the pipes and runnels that supply I. 8. What is the present mean and variability over time of discharge to L? Is there any leakage in I? 9. Would there be enough water supply to reintroduce J and what was the historic pathway for the outlet (K)? Would it still be feasible to utilise K as an output flow pathway or are other alternatives more feasible? 10. Would it be feasible to re-route water from L in order to feed water from I into M through to N so that the artificial water features would be adequately supplied to operate? This analysis relies on information from questions 7, 8 and 9 but also requires analysis of best management for the cascade valley. For example it may be necessary to ensure that routing the water through M and N does not result in seepage loss through old features. 11. In light of these research questions the report should also make recommendations for the sustainability of particular management options. If water was diverted from D, for example, would that impact soil moisture conditions in the surrounding areas and destabilise vegetation growth. In particular the report will need to show how the water features would be sustainable throughout the year under a range of antecedent conditions. In other words some attention will need to made towards establishing how the springs and other inputs and outputs (e.g evaporation from the ponds) vary seasonally so that predictions can be made as to the performance of restored water features during the year. Instrumentation will be 5

12 required for continuously monitoring spring yields through the year and during storm events. In its simplest form the budget work will require automatic logging of discharge from the two known spring areas and logging of discharge input into the T pond and Obelisk features. Leakage in the clay and earthen lined pipes and runnels supplying water from the springs can then be established but it will be necessary to supplement this with manual sampling. Rated sections could be used and the work will probably not necessitate the use of weir structures. 12. In addition to the research questions highlighted above the research should establish whether there are any other feasible sources of water in the catchment that may be used to supply the artificial water features. The park is roughly 35 ha, but the topographic catchment area is slightly larger and the springs may be supplied from a subsurface catchment outside of the topographic catchment area. The limitations associated with the data and survey methods should be made explicit and included in any feasibility suggestions. Documentary and archaeological evidence suggests that there were some small storage reservoirs in the catchment. The report should discuss the utility of these and the sustainability of their use within the catchment with respect to feasible re-introduction of water features and permeability of the underlying substrate. 2.3 Aims and scope of this report This report aims to address all of the issues raised in Table 1 above. While those points indicated in blue were examined in the first report, which detailed results of the geophysical survey, they will necessarily be revisited so that a full set of findings and recommendations can be made available. Hydrological data discussed in this report are available from mid July 2002 to June 2003 and hence allow seasonal variations to be analysed. 6

13 3. Methodology and monitoring locations 3.1 Monitoring instruments Three main springs supply the artificial water features in the formal gardens as shown in Figure 2. In order to establish the yield and variability of water supply from these springs it was necessary to gauge their discharge (the volume of water they produce in a given period of time; e.g. litres per second). Gauging sites were located as close as possible to the spring outlets but had to be sited where a suitable installation site could be found. The instruments had to be carefully located in order to i) minimise local disturbance to the banks and bed; ii) avoid the instrument becoming silted up; iii) to allow small changes in spring discharge to result in maximum changes to water level near the instrument this provides greater accuracy in the measurements made. In addition to the three spring flow gauges seven other hydrological monitoring instruments were installed within Bramham Park in order to provide information on the contemporary hydrology (Figure 2). Results from these instruments combined, provided long-term information on inputs, outputs and leakages from the various components of the system. Importantly they provided information on the nature of the discharge from the springs that supply the garden s artificial water features, and therefore whether the original features can be feasibly restored. As shown in Figure 2 the water level recorders were located at the spring outlets (1, 3, 4 e.g. Figure 4b), downstream of the confluence of the two Jenny Sober springs just before the water enters the pipe leading to the Obelisk ponds (5) Figure 4c, in the pipe immediately upstream of the T pond (2)- Figure 4a, in the surface channel upslope of the Half Moon and Obelisk ponds near the Gothic Temple (6) and one at the entrance to the Half Moon Pond (7) Figure 4d and e Water level recorders These instruments (the smallest of their type in the world), as shown in Figure 3, were set to record water levels at 15 minute intervals at seven sites throughout the Park. Water levels were recorded to the nearest mm and were temperature compensated. Water temperatures were also recorded by the instruments. Each DIVER pressure transducer for water level recording was housed inside a stilling well. The purpose of the stilling wells was twofold; i) to protect the pressure transducer housed internally from damage caused by gravels hitting the instrument during high flow events; ii) to provide a more accurate determination of water level in a stream as the stilling well removes the affects of stream turbulence. The wells consisted of short narrow pieces of cylindrical drainpipe positioned into stream channels. The instrumentation design recognised the importance of landscape conservation within Bramham Estate and endeavoured to create very little disturbance. The instrumentation was such that it is highly unlikely that once the instruments are removed, there will be any noticeable traces of instrument presence. Where possible, instruments were placed under manhole covers or adjacent to earthen banks where disturbance would be unrecognisable once the instruments are removed. Figure 4 shows some of the instrumented sites. 7

14 0 metres 500 N Water level recorder Air pressure recorder Rain gauge Monitored water course Figure 2. Location of hydrological instruments installed at Bramham Park 8

15 loop Figure 3. The DIVER pressure transducer. a) b) c) d) e) Figure 4. Some monitoring sites; a) inside manhole just upstream of the T Pond site 2; b) site 3 in the Jenny Sober plantation; c) at site 5 where water from sites 3 and 4 combine and enter a pipe to feed the Obelisk Ponds; d) inside manhole at the Half Moon Pond inlet; e) View of Half Moon pond manhole. 9

16 3.1.2 Air pressure recorder Two pressure transducers were placed above water to compensate for changes to atmospheric pressure at the locations shown in Figure Rain gauge One cylindrical tipping bucket rain gauge was installed on site (Figures 2 and 5). The gauge was fixed to the ground via a wooden base plate to usual hydrological measurement standards and recorded rainfall in 0.2 mm intervals. 250 mm Figure 5. Tipping bucket rain gauge 300 mm 3.2 Data calibration and analysis. At each of the seven water level recording sites it was necessary to produce a calibration that related any given water level to a discharge so that a water budget could be created. In order to do this the discharge at each site was measured using standard hydrological techniques (e.g. dilution gauging, velocity-area gauging, Herschy, 1999) on at least 10 occasions. This allowed an equation to be developed for each site that meant that all water level measurements could be converted to discharge measurements. These techniques are those universally adopted by hydrologists and are Environment Agency standard practice. It is important when calibrating water levels to discharge values at any stream flow gauging site to ensure that a wide range of values are obtained. In other words the calibration was required at low flows, high flows and intermediate flows so that we could place trust in the values provided. Thus, for each site a calibration plot could be drawn which allowed an equation to be formed. Since measurements across the site were performed simultaneously on an automatic basis every 15 minutes it was then possible to examine discharge through the system in response to rainfall events on a 15-minute, hourly, daily and monthly basis in order to determine trends. 3.3 Other data sources Additional rainfall data were obtained from the Bramham weather station located 3 km due east of the T pond (National Grid Reference SE ). Here rainfall data are available from 1960 to present allowing the current monitoring period to be placed within a longer term context. 3.4 General hydrological audit of the Estate A site survey was carried out between August 2002 and March 2002 by Geocat in order to determine the location and status of hydrological features within the Bramham landscape. The aims of this survey were to i) identify and record existing hydrological features; ii) to identify those hydrological features that are in need of conservation, repair, restoration or removal; iii) to prioritise the urgency of the above needs. 10

17 4. Results of hydrological monitoring Figure 6 shows a conceptual sketch of the numerical coding applied to the monitoring sites that will be discussed below and as indicated in Figure 2. The Whittle Carr spring (1) supplies water to the T Pond (2) and two springs in the Jenny Sober plantation (3,4) supply water to a single pipe (5) that then feeds the Obelisk Ponds near the Gothic Temple (6). When the T Pond is full water from this also supplies the Obelisk Pond so that it was necessary to put an extra gauge at the input to the Obelisk Ponds (7) that measured the total input (overflow from the T pond plus flow from Gothic Temple stream). The link between the T Pond and the Obelisk Ponds is an important one, but was not an original feature of the landscape design. This link will be discussed in more detail later. 7 Obelisk Ponds T pond Jenny Sober 3 Whittle Carr Figure 6. Connectivity of gauging sites. Figure 7 shows the total discharge measured from 1 st August 2002 to 31 st May 2003 at each of the gauging sites. The proportional circles help illustrate the nature of gains and losses between sites. Between Whittle Carr and the T Pond there are large gains in water over the study period. However, between the Jenny Sober springs and site 5 there are large losses. Very little water from the T Pond appears to reach the Obelisk Ponds to supplement the supply from the Jenny Sober plantation. There also appears to be some losses (9400 m 3 ) between sites 5 and 6 which is the system from the intake pipe in the Jenny Sober woods to the Obelisk Ponds. 11

18 80.0 Obelisk Ponds T Pond Jenny Sober 29.1 Whittle Carr Figure 7. Amount of water in 1000s of cubic metres that flowed through the measurement points between 1/8/02 and 31/5/03 with proportional circles. Values for Whittle Carr spring have been estimated for Jan and Feb 2003 by calculating the mean proportion of flow for all other months in relation to the T Pond. While Figure 7 suggests a very simple system of leakages and gains there are also important seasonal differences which help elucidate the nature of the site. Figure 8 shows the monthly discharge totals for each site. The gauging at site 1 was interrupted in January 2002 due to disturbance but this was repaired during February. However, there is a full record at all other sites. Rainfall was not evenly distributed during the year with low rainfall during September, January, February and March but a more typical autumn wetting up period. For groundwater in the UK, the water tables tend to rise during the autumn and through the winter so that groundwater discharge also increases at this time. Groundwater is usually at its lowest during late summer as rainfall is slightly lower and seepage to the bedrock is reduced by plant and evaporative uptake from the soil. 12

19 a) b) rainfall, mm Aug Sep Oct Nov Dec Jan Feb Mar Apr May c) d) discharge, 1000s m Aug Sep Oct Nov Dec Jan Feb Mar Apr May discharge, 1000s m 3 discharge, 1000s m Aug Sep Oct Nov Dec Jan Feb Mar Apr May Aug Sep Oct Nov Dec Jan Feb Mar Apr May e) f) discharge, 1000s m Aug Sep Oct Nov Dec Jan Feb Mar Apr May discharge, 1000s m Aug Sep Oct Nov Dec Jan Feb Mar Apr May g) h) discharge, 1000s m Aug Sep Oct Nov Dec Jan Feb Mar Apr May discharge, 1000s m Aug Sep Oct Nov Dec Jan Feb Mar Apr May Figure 8. Monthly discharge totals from the gauging sites; a) Rainfall, b) Site 1, c) Site 2, d) Site 3, e) Site 4, f) Site 5, g) Site 6, h) Site 7. 13

20 Sites 3 to 6 all show similar patterns because they are part of the same Jenny Sober system. Site 7 matches site 6 until November 2002 and then matches it again after March The period in between when the discharge is not matched is the period when the supply to the T Pond was great enough that it filled sufficiently to flow into the Obelisk system. The T Pond currently leaks but when enough water enters the T Pond, it can fill so that it reaches the level of an overflow pipe which takes water to the Obelisk Ponds. These data can therefore easily be used to identify the times at which the T Pond was full and supplying extra water to the Obelisk system. This occurred during November 2002 and January, February and March 2003 but not during the other months. Thus most of the water being delivered to the T Pond is currently leaking away. This is of crucial importance to the entire water garden because as Figure 7 shows the biggest flow in the gardens comes into the T Pond at site 2 and so the Whittle Carr system produces the biggest discharge. This is despite the fact that the Whittle Carr spring itself does not produce the largest flow and in fact the Jenny Sober springs produce more discharge than Whittle Carr (Figure 7). Thus, it is not necessarily the amount of water coming from the springs themselves that it important, but how extra water gets into the supply system in some parts and how across other parts of the system water is lost. These features will be the discussed in detail below. One of the main problems with spring supply is that it is much lower in the summer than in the winter period. One would expect this to be the case but the period when the artificial water features in the gardens would be required to operate with a good flow would be during the summer when visitors to the grounds are greatest. Figure 9 shows the discharge for every 15 minutes since monitoring began on 15 th July until 3 rd June The system appears to be dominated by summer low flows and then a more variable winter period where some rainfall events can have a very big impact on the discharge of the system. This indicates that the groundwater wets up in the autumn so that when it is sufficiently saturated any big rainfall event can easily produce a big response whereas a big rainfall event in the summer simply acts to replenish the groundwater and does not result in large discharge events. discharge, litres s rain, mm rain Q 1 Q 2 Q 3 Q 4 Q 5 Q 6 Q days since monitoring started Figure minute discharge for all sites from 15/7/02 to 3/6/

21 There are thus two main concerns here for the workings of the water gardens: i) the potential for large winter discharge events to overtop the features ii) the low summer flows If summer discharges to the water gardens are maximised by reducing leakages and taking other measures (see below) then care will have to be taken to ensure that there are sufficient overflow systems during high flow events in the winter so that the system is not damaged. Figure 9 shows all of the gauging results on one plot, which makes individual differences difficult to identify. Therefore, Figure 10 has separated out some of the components so that closer inspection of the trends can be made. Figure 10b shows the much higher flow recorded at the T Pond input pipe (2) than emerges from Whittle Carr spring for most of the year. Figure 11 shows that for almost every day of the study period discharge increased between the two sites. Sometimes the discharge can increase by up to 400 % although on average the T Pond input has flow that is around 2.5 times greater than the Whittle Carr spring. Figure 10c provides a plot showing discharge over the study period for the Jenny Sober system. As would be expected site 5, which is downstream of the confluence of the two springs, generally has a greater discharge than either of the springs. However, there are some high flow periods when one of the springs (4) produces much greater discharge than is measured downstream. Clearly a lot of water is lost during periods of high discharge through leakage between these points. Figure 12 shows the magnitudes of gains and losses between the sites and suggests that sometimes 100 % more water is added to the system through direct rain into the ditches and drainage from the slopes next to the ditches whereas during high flow events 50 % of the water can be lost through leakage from the Jenny Sober ditches. The fact that so much extra water can be added during dry periods to the Jenny Sober or Whittle Carr systems suggests that they should not be piped for their entire length to the source of the springs. However, the losses during wet periods may need some attention, not least because leakages during storms could make the system much worse during later dry periods. Figure 10d illustrates that there is very little difference in the discharge at site 5 and that at site 6. These sites are mostly piped between them suggesting that the pipework has few leakages. However, examination of Figure 13 shows that most of the time some water is being lost between sites 5 and 6. There is only a short 50 m reach upstream of site 6 where the water is in an open channel. There may be some losses from this channel through seepage and evaporation and over bank flow during storm events. Tests showed that there was no discernable leakage from any of the pipework between site 5 as it traversed through the Rough Pasture to site 6 upstream of the Obelisk Ponds. Instead all of the losses were found to be occurring at the intake pipe location at site 5. Water frequently leaks from this site from the intake ditch away from the pipe rather than entering the pipe. Figure 14 shows a photograph of this leak. Some simple repairs at this intake point would help reduce these losses and increase flow to the Obelisk ponds by 13 % overall. It is noted that some temporary repairs were made to this system during February 2003 by Estate workers but these will be insufficient over longer periods. Nevertheless, these repairs temporarily stopped the leaks as can be seen around day 220 on Figure 13b where the percentage lost was reduced from around 30 % to zero. After 25 days these temporary repairs failed and the leak started up again around day 245. Figure 10e shows periods when the T Pond input at site 7 is exactly the same as that at site 6 and other times when it is much greater. Those times when it is the same are when the Jenny Sober springs are the only source of water to the Half Moon Pond inlet. At those times when the discharge is much greater this is when the T Pond has filled sufficiently so that the overflow pipe in the T Pond becomes operational and sends flow to the Half Moon system. 15

22 a) 0 days since monitoring started rainfall, mm in 15 minute periods b) dishcarge, litres s Q 1 Q days since monitoring started c) 45 discharge, litres s Q 3 Q 4 Q days since monitoring started 16

23 d) Q 5 Q 6 discharge, litres s e) days since monitoring started Q 6 Q 7 discharge litres s f) discharge, litres s days since monitoring started Q 1 Q 3 Q days since monitoring started Figure minute discharge at sampling points with a) rainfall, b) to f) comparisons 17

24 a) daily discharge, m missing data days since monitoring started b) % Q2 greater than Q missing data days since monitoring started Figure 11. Daily gain in discharge between the Whittle Carr spring and the T Pond input a) total discharge gained, b) percentage discharge increased. 18

25 a) daily discharge, m days since monitoring started b) 150 % Q5 greater or less than (Q3 + Q4) days since monitoring started Figure 12. Daily gain or loss in discharge between the two Jenny Sober springs and site 5; a) total discharge gained, b) percentage discharge increased or decreased. 19

26 a) daily discharge, m b) days since monitoring started % Q6 greater or less than Q days since monitoring started Figure 13. Daily gain or loss in discharge between site 5 and site 6; a) total discharge gained, b) percentage discharge increased or decreased. 20

27 Figure 14. Leak from side of intake pipe at site 5 in the Jenny Sober plantation. Figure 10f plots the discharge from the three monitored springs. The Whittle Carr system (Q1) has a slightly more reliable flow during summer dry periods than Jenny Sober springs and indeed the Landscape Agency (2001) report that the Jenny Sober springs can sometimes dry up during the summer (e.g 1933) whereas Whittle Carr continues to flow. This is probably why Whittle Carr supplied water to the house until the 1960s. During very wet periods Figure 10f shows that Q4 can be much higher than the discharge from the other springs. Site 4 is the spring in the Jenny Sober plantation that rises in the southwest (see Figure 2). Interestingly during dry conditions water issues only out of the rock on the floor of the ditch at this point. However, during wet conditions the groundwater rises sufficiently so that surface water is also generated as overland flow to this point and the stream channel itself extends back much further up the valley in the woods (see Section 6.3). The shape of the hillslope lends itself to drainage at this point so that in the winter a stream exists in the valley floor among the trees well upstream of the spring outlet. In the summer this stream is dry and only water coming out of the spring supplies the ditch. This feature of a stream extending further up valley during wet periods is common in groundwater dominated areas and indeed where abstraction has taken place often streams dry up in their upper reaches until much further downslope where they cut into the water table. Water from all three springs appears to be supplemented by water draining into the ditches that carry the spring water to the water gardens. However, this only occurs in certain places and will not occur in those areas, particularly in the Jenny Sober plantation, where the ditches are raised above the surrounding topography. Here only direct in-channel rainfall will add to discharge. However, several small tributaries from the surrounding hillslopes add water to the ditch systems and in many places water seeping from the soils and rocks surrounding the ditches can enter the drainage system. Figure 15 shows photographs of water seeping into one of the ditches in the Jenny Sober plantation. Water seeps through the rock into the ditch adding more water to the system along the course of the stream and thus increasing available supply to the formal features in the gardens. 21

28 Figure 15. Water seeping and dripping into the Jenny Sober supply ditches through the rock. Extra input from the surrounding topography appears to be particularly important in the Whittle Carr system. This is because there is a large topographic catchment area that drains into the intake pipe for the T Pond downslope of Whittle Carr. The intake pipe is located at the outflow from a pond. The pond itself has a large area of slopes feeding water into it (Figure 16) in addition to that supplied by Whittle Carr spring. Figure 16. Pond downstream of Whittle Carr Grotto with arrows indicating slopes that feed water into the pond that then goes on to supply the T Pond. 22

29 60 50 discharge, litres s days since monitoring started Figure 17. Sum of discharge at site 2 and site 5 15/7/02 18/3/02 When the water flowing into the T Pond from Whittle Carr and water flowing from Jenny Sober towards the intake pipe are added together, Figure 17 shows that even during dry summer periods there are typically over 5 litres s -1 of water available. This is more than double that which generally flowed through the Half Moon and Obelisk ponds during summer This is therefore very good news in terms of potential restoration of some of the water features. 23

30 5. Combining hydrological results with archaeological data and water needs 5.1 Sites in need of complete restoration. The Landscape Agency report (2001) provides maps of two cascade systems that currently do not operate. Archaeological work was conducted on one of these cascades (Obelisk Pond cascades) and results are discussed in two reports (York Survey and Research, 1990; York Archaeological Trust, 1991). However no archaeological work was carried out on the cascade system located in front of the house and which was supplied by a pool known as Queen s Hollow (Figure 18b). Importantly the first Geocat report (Holden et al., 2002) showed that the Queens Hollow was originally supplied by water from the T Pond. This cascade is reported to fall 21 feet on thirty steps according to a plan of Bramham Park by John Wood the Elder c1728. The Obelisk Pond cascades ran south-eastwards from the Obelisk Ponds to another pool on the valley floor which then supplied two other sunken pools in what is now called Cascades Valley (Figure 19). Instead, today, water bypasses these cascades and runs via a pipe out along Cascade Valley towards Bramham Beck (see Figures 52 and 56). In addition to these two pool and cascade systems that no longer operate, the most north-western part of the Obelisk Ponds no longer operates. This is pool is known as the Sub-Tropical Garden and is shown in Figure 20 and is thought to have been drained in the mid-19 th century. A map of the features in question is shown in Figure 21. a) b) c) Figure 18. Queen s Hollow and Parterre; a) Parterre looking towards Queen s Hollow; b) Queen s Hollow; c) View from Queen s Hollow towards Parterre. 24

31 a) b) c) Figure 19. Obelisk Pond cascades. a) and b) Excavated cascade system (Photo courtesy of English Heritage, originally provided by York Archaeological Trust; c) Upper Obelisk Pond Cascades/waterfalls during January 2003 when sufficient water supply was available to make the cascade system look operable. a) b) Figure 20. Sunken side pond on the northwest of main Obelisk Pond. This feature is known as the sunken garden and would have originally had water pouring out of two beasts mouths into the pool. Today this feature is grassed over and is known as the Sub-Tropical Garden. 25

32 Site of 30 step cascade running into Parterre N 0 Metres 200 A B C GPR located pipe Probable course of historic inactive pipe Course of active pipe Sub-tropical garden Two further pools are shown on some old plans of Bramham Figure 21. Plan of features in the formal garden 26

33 5.2 Water needs of features Queen s Hollow and Parterre cascade Queen s Hollow itself would not require a regular supply of running water to become a feature as long as it was relined and watertight. However, water from the T Pond could be channelled to the Queen s Hollow which would then overflow to the cascade towards the House and Parterre. The main requirement for the restoration of the Queen s Hollow cascade would be the amount of water needed to make this appear an attractive feature. While a small discharge might be possible this would not be aesthetically pleasing. However, the amount of water necessary to achieve this is subjective and will depend on the width of the cascade system. Indeed it may well have been the width of the cascade features that was one of the problems with the original design and led to their downfall. There are no data on the width of the cascades at this site. If they are the same width as the remnant Obelisk cascades then they would be 4 metres wide. In order to have an appealing effect across a 4 m width cascade, given the slope at the site, the water would need to be moving at a mean velocity of around 10 cm s -1. With a mean water depth across the cascade system of only 2 cm (again this would be subjective but very little water depth would be needed as a minimum) the minimum flow that would be required would be 0.02 x 4 x 0.1 = m 3 s -1. This is equivalent to 8 litres per second. If the cascade was designed to be different widths then the values shown in Table 2 would be required. A 4 m wide cascade provided with 8-10 l s -1 would supply a sufficient amount of water to the rose garden feature so that it did not look overpowered by the water. Table 2. Approximate water requirements of the Queen s Hollow Cascade Cascade width, m Minimum discharge needed, litres s One option would be to restore the Queen s Hollow and then pipe water directly from the Queen s Hollow to the mouth of the mythical beast at the head of the rose garden. Water would then flow down the existing stone water feature and into a pool at its base. The hollow for the pool is visible at the site. The Parterre pool at the foot of the cascades would again not require a minimum amount of flow to operate as long as it was relined. However, both the Queen s Hollow and Parterre pool would require adequate overflow drainage to send water back towards Cascade Valley Obelisk Pond cascades As with the Parterre cascade system a similar minimum amount of water would be needed to make the features look attractive since the archaeological work showed the steps to be 4-5 metres wide. This would be equivalent to the amount of water leaving the Obelisk Pond as shown in Figure 19c. This photograph was taken in January 2003 when there was enough water available (8 to 10 litres s -1 ) for the cascade features to be operated adequately. However, as we have seen above there would not be enough water during the summer period to operate this feature when only supplied by Jenny Sober springs. Restoration of the three pools (or even just one pool) at the foot of the Obelisk pond cascades on the floor of cascade valley would again not require a constant supply of water and they could be restored as static water features. Furthermore water could be piped through to them from the Obelisk ponds (bypassing the original cascades) or a set of narrower cascades could be created. 27

34 5.2.3 Obelisk pond sub-tropical garden. If this feature was to be restored as a pool it could be done so either as a static water feature or as one supplied by the central Obelisk Pond with water flowing through the mythical beasts mouths. If the latter is to be considered this would mean half of the water that currently leaves the Obelisk Pond by the current outlet would have to be diverted to the Sub-tropical garden. As summer supply from Jenny Sober stands at the moment this would not be feasible since it would look as if just a small flow is emerging. However, in autumn and winter the effect would look good. Water would also need to have an exit from the restored side pond even if the pond was static and not supplied by flowing water. This is because rainwater could cause the pond to overtop. The overflow could either be redirected eastwards across the paddock towards Bramham Beck or, preferably towards the restored cascades and Cascade Valley. This would essentially mean that water supply to the cascades would not be reduced by the reintroduction of the side pond as the water would be used twice Obelisk Fountain There have been some suggestions that there was a fountain in the centre of the Obelisk Ponds. Study of the groundwater shows that there would not be enough hydraulic head (pressure) to be able to lift it above the surface of the pond solely by the force of gravity. Thus, if a fountain is to be re-established to the Obelisk Pond system it would have to be powered by other means. This may be outside the remit of English Heritage given their role in conservation and repair rather than addition of new features. Some proof would have to be found of the existence of such a feature but it is not likely that there was ever a fountain. It is more likely that there was a statue at this location. 5.3 Water supply, water needs and climate change If water features at Bramham are to be restored using groundwater sources it will be important to assess whether future climate changes may serve as a potential threat to the features. Figure 22a shows the mean monthly rainfall at Bramham since There have been no significant changes in annual rainfall totals or rainfall seasonality at Bramham since that date. While the plot shows that rainfall is quite evenly spread during the year there are seasonal controls which are better illustrated by Figure 22b which groups rainfall totals into three month clusters. The autumn months of September, October and November are the wettest. However, there is significant year to year variability in rainfall totals at Bramham (Figure 22c) with a maximum of 801 mm (1986) and minimum of 420 mm (1975). Given this range and the fact that the groundwater springs at Whittle Carr and Jenny Sober have been shown to be heavily dependent on antecedent rainfall totals it is likely that the performance of water features would vary greatly depending on the conditions in any given year. In some years the features may function very well even during the summer, whereas in others they may not function well even during the winter. Figures 23a and b show climate change scenarios obtained from the UK Climate Impact Programme (Hulme and Jenkins, 1998). These are for estimated percentage changes in precipitation for both winter (Figure 23a December, January, February) and summer (Figure 23b June, July, August). Three dates are available: 2020, 2050 and 2080, for four different scenarios of the rate of climate change. Figure 23a shows that climate change scenarios suggest an increase in winter precipitation throughout the UK for all rates of climate change. For the region around Bramham this is estimated to be between 5 and 10 % by the 2020s, with increases maybe as high as % for the more rapid rates of warming for the 2080s. These observations suggest that the 21st century will see much wetter winters in some parts of the UK, which would be expected to produce higher river flows. If, as hypothesised, this is manifest as more frequent extreme rainfall events, the magnitude and frequency of river flooding 28