Monitoring a flood event in a densely instrumented catchment, the Upper Eden, Cumbria, UK

Monitoring a flood event in a densely instrumented catchment,the Upper Eden, Cumbria, UK

W. M. Mayes, C. L. Walsh, J. C. Bathurst, C. G. Kilsby, P. F. Quinn, M. E. Wilkinson, A. J. Daugherty & P. E. O’Connell

School of Civil Engineering and Geosciences, University of Newcastle upon Tyne, UK

Keywords

catchment hydrology; CHASM; flood;

catchment management; rainfall; scale effects.

Correspondence

C. L. Walsh, Newcastle University, Newcastle,

UK. Email: [email protected]

doi:10.1111/j.1747-6593.2005.00006.x

Abstract

Multi-day rainfall events appear to be an important cause of recent flooding in

the UK. Hydrological data from an extensive, nested hydrometric network in

the unregulated, predominantly rural Upper Eden catchment in northern

England are presented for one such flood event. These highlight antecedent

catchment conditions and the propagation of the multi-day flood event during

February 2004. An assessment of flood response is provided over varying scales

and land use between the upland Gais Gill catchment (1.1 km2) and the larger

Upper Eden catchment (616 km2). Large spatial variations in rainfall totals are

identified from a dense raingauge network during the flood event and are

principally related to catchment elevation. High cumulative rainfall totals for

the 6-day event, particularly at upland sites appear to be the exceptional

feature of the flood event with return periods in the order of 100 years at some

upland gauges. Resultant patterns of flood attenuation and translation are

quantified in different areas of the catchment, highlighting the flashy response

of the headwater catchments and the attenuated downstream response in the

lowland environment. The study forms part of the national Catchment

Hydrology And Sustainable Management (CHASM) programme.

Introduction

There is an estimated d220 billion worth of property and

d7 billion worth of agricultural land located within po-

tential flood risk areas in the UK (Ministry of Agriculture,

Fisheries and Food 2001; Purnell 2002). Although recent

investment by the UK government in flood and coastal

defence is claimed to have reduced potential average

annual losses from d3.5 billion to d0.8 billion (Purnell

2002), large areas of land and riparian settlements remain

at risk from flood events. Recent projections suggest that

average annual losses from flood damage could increase

to up to d27 billion in the 2080s under a worst-case

climate change scenario and unchanged government

flood management policy and expenditure (Office of

Science and Technology 2004).

The intensity and duration of multi-day rainfall events

are one of the principal controls on flood severity in the

UK. Detailed monitoring and analysis of the development

and response of such events from plot scale (o100 m2) to

catchment scale can aid the construction of the predictive

tools (e.g. hydrological computer models) which under-

pin the formulation of sustainable integrated land use and

flood management strategies. The data presented here

represent one such event for a densely instrumented

catchment in northern England during early February

2004. The 322 km2 Upper Eden catchment in Cumbria

(above Appleby-in-Westmorland) is one of the four ex-

perimental catchments in the UK Catchment Hydrology

And Sustainable Management (CHASM) catchment hy-

drology initiative (O’Connell 2003) (www.ncl.ac.uk/

chasm). The CHASM initiative endeavours to investigate

many of the fundamental issues in catchment hydrology

and management (e.g. land use, flooding, abstractions,

water quality and ecology) and to bridge the gap between

plot scale and meso-scale (100s of km2) catchment re-

sponse, using nested multi-scale monitoring networks.

The ‘scale problem’ has been identified by many observers

as a major unresolved issue in hydrology (National Re-

search Council 1991; Newson 1994; Bloschl & Sivapalan

1995; Sivapalan & Kalma 1995; Archer 2003). Catchment

experiments are predominantly undertaken at a small

scale (o10 km2) but only limited aspects of the hydro-

logical understandings obtained can be transferred to

the larger scales at which river basin management is

conducted. The multi-scale, dense network therefore

provides an unusually detailed record of the development

and progression of a flood sequence in a catchment. In

Water and Environment Journal 20 (2006) 217–226 c� 2006 The Authors. Journal compilation c� 2006 CIWEM. 217

Water and Environment Journal. Print ISSN 1747-6585

addition, the longer term findings of the CHASM initia-

tive will inform future sustainable river basin manage-

ment, through improved knowledge of catchment

processes, response and anthropogenic impact.

Integrated data from an extensive network of hydro-

metric equipment in the catchment (including river

gauges, raingauges, automatic weather stations, soil moist-

ure probes) are presented to describe: (1) the antecedent

catchment conditions leading up to the flood event from

the previous autumn, (2) the catchment response over

varying scales up to around the 600 km2 basin size during

the event and (3) variations in response between areas of

different land use within the catchment. The flood event,

which spanned 6 days from 30 January 2004, caused

widespread flooding of lowland farmland in the study

catchment and of the downstream riparian city of Carlisle.

More recent severe flooding in the catchment in January

2005 has further highlighted the flood risk issue in the

catchment and the need for an improved understanding of

the mechanisms controlling the development and propa-

gation of flood waves through the basin.

Study site

The Eden catchment covers an area of 2288 km2 to its

outlet via the Solway Firth to the Irish Sea, draining parts

of the Lake District and Pennine Hills of northern Eng-

land. The study area reported here encompasses the upper

catchment above the town of Temple Sowerby and covers

an area of 616 km2 (Fig. 1). The upper catchment drains

the western slopes of the Pennines with elevations ran-

ging from the highest point at High Scald Fell [788 m

above ordnance datum (AOD)] in the far north of the

CHASM catchment to approximately 93 m AOD near the

gauging station at Temple Sowerby. The River Eden itself

rises on the limestone hills of Mallerstang Common, on

the border of Cumbria and Yorkshire, flowing northwards

through the settlements of Kirkby Stephen and Appleby-

in-Westmorland. Important tributaries of the Eden within

the study catchment include the Scandal Beck, the

River Belah and Swindale Beck (Fig. 1). The 200 m

contour is taken here to separate the upland and lowland

components of the upper catchment. The lowland envir-

onment is characterized by the River Eden floodplain and

a drumlin field, while the upland environment is char-

acterized by steeper gradient terrain and moorland in-

cluding areas of blanket peat mire.

There are large variations in rainfall across the catch-

ment because of the elevation differences and the rain-

shadow effect from the Lake District Hills to the west.

Annual rainfall totals range from less than 650 mm in the

lowland valley to more than 2000 mm in the upland parts

Appleby

Brackenber

Great Musgrave

Kirkby Stephen

Lunds Fell

Aisgill

Stennerskeugh

Angerholme Pots

Artlegarth

Scandal Beck River

Eden

River Belah

Swindale Beck

TempleSowerby

Blind Beck

Warcop×

CHASM automatic weather stationsCHASM raingaugesCHASM stage gaugesExisting stage gaugesExisting raingaugesExisting automatic weather stationRiver EdenCHASM catchment to Appleby Gais GillTemple Sowerby catchment

Kilometres

N

0 2010

Fig. 1. Location map of the Upper

Eden study catchment. CHASM,

Catchment Hydrology and Sustainable

Management.

Water and Environment Journal 20 (2006) 217–226 c� 2006 The Authors. Journal compilation c� 2006 CIWEM.218

Monitoring a flood event in a densely instrumented catchment W.M. Mayes et al.

of the catchment. Runoff is controlled by differences in

topography and geology, with flashy runoff and small

ephemeral streams characterizing the uplands where

there are steep slopes and little soil cover, and greater

groundwater contributions from the lowland limestone

and sandstone aquifers. Livestock farming is the domi-

nant land use in the catchment, particularly in the low-

land areas, while upland land use is dominated by lower

intensity livestock farming, with rough pasture and some

forestry.

Snow cover in the catchment can be significant during

the winter months and snowmelt, especially when

combined with heavy rain, can lead to flooding. The

Eden catchment as a whole has five formal flood warn-

ing zones, as well as flood alleviation schemes at

Appleby and downstream at Carlisle, highlighting the

importance of flood risk in the catchment. Important

recent floods in the catchment occurred in 1968 and

2005 severely affecting settlements from Appleby to

Carlisle, while less severe events affected the Eden Valley

in 1997, 1998 and 2000.

Extensive hydrometric instrumentation of the Upper

Eden catchment was carried out between 2002 and 2004

as part of the CHASM catchment hydrology initiative,

supplementing existing Environment Agency (EA) dis-

charge gauges (at three locations) and raingauges (at nine

locations). Eight stage gauges within nested catchments

monitor river levels in contrasting areas of land use (up-

land and lowland) at scales from micro-catchment

(1 km2), through mini-catchment (10 km2), up to meso-

scale (100 km2) as outlined in Fig. 1. Data from Gais Gill

(catchment area 1.1 km2), Artlegarth House on Artlegarth

Beck (2.7 km2), Smardale on Scandal Beck (36.6 km2)

and Blind Beck (9.2 km2) are presented here along

with data from the existing EA stations. All stage and

discharge gauges record at 15 min intervals. The Gais Gill,

Artlegarth House, Smardale and Blind Beck gauging

stations have been rated with current meter gauging by

wading, while the existing EA stations at Kirkby Stephen

(69.4 km2), Great Musgrave (222.5 km2) and Temple

Sowerby (616.4 km2) sites have been rated with current

meter gauging via wading and suspension cable.

A network of 11 event-recording tipping-bucket rain-

gauges across the catchment at a range of elevations (from

155 m AOD at Great Musgrave to 650 m AOD at Lunds

Fell) supplements the existing EA Eden raingauge net-

work (Fig. 1). This existing network comprises nine rain-

gauges covering a range of elevations (from 148 m AOD at

Appleby to 360 m at Aisgill) and recording at various time

frequencies from event to daily. Multi-parameter data

(including air temperature, relative humidity, wind speed

and direction and net radiation) from automatic

weather stations (AWS) at Gais Gill and Great Musgrave

provide meteorological data for calculating evapo-tran-

spiration.

Further hydrometric monitoring within the catchment

includes groundwater monitoring at three sites, the focus

of which consists of over 15 paired drift and sandstone

boreholes assessing river–aquifer interactions on the Riv-

er Eden at Great Musgrave. Additionally, soil moisture

and soil water table regime data are obtained from a series

of multi-level, shallow, water table piezometers (o2 m

depth) with 15 min recording pressure transducers

and soil moisture probes (Delta-T MLX Theta Probes,

Cambridge, UK). This instrumentation is concentrated

within a plot-scale (o100 m2) sampling design at three

hillslope and one floodplain location at Great Musgrave.

A series of nested multi-level piezometers at Gais Gill also

provide soil water table regime data from the upland

micro-catchment. The density of instrumentation is (gen-

erally) unequalled at this scale of catchment in the UK.

Results and discussion

Temporal context of the flood event

Figure 2 shows the fluctuations in rainfall, stream dis-

charge and soil water table levels in the lowland environ-

ment around the Great Musgrave site from the end of

summer 2003 to February 2004. The dry summer that

affected much of England during 2003 is apparent in the

low rainfall totals and baseflow-dominated regime for the

River Eden in September and October 2003, with isolated

storm events leading to rapid rise and recession of river

levels (e.g. 22/9, 4/11). Towards the end of 2003, the

frequency of storm events increases with several events

peaking around 20–100 m3/s at Great Musgrave in late

December to early January 2004. This seasonal transition

is particularly pronounced in the soil water table records

from floodplain locations at Great Musgrave. A general

rise in water levels in excess of 1 m is apparent between

September 2003 and January 2004. This recovery from

intense summer drawdown in soil water table levels

continues at the Great Musgrave floodplain locations up

to the overland flow conditions that occur during the

flood event.

Field observations during the week preceding the flood

event recorded moderate snow fall on 28 and 29 January,

with a light covering (o5 cm) of snow above �450 m

AOD, thawing on 30 January. These field observations are

corroborated in part by air temperature records (Fig. 2),

which show a rapid rise from daytime temperatures as

low as � 4.3 1C on 28 January up to daytime tempera-

tures in excess of 10 1C on 31 January during the second

band of intense rainfall at the Gais Gill upland catchment.

No clear signal of snowmelt can be seen within discharge


Monitoring a flood event in a densely instrumented catchmentW.M. Mayes et al.

records at any of the gauging sites (as this is likely to be

hidden within rises associated with the onset of rainfall

on 29 January). However, the resulting antecedent catch-

ment wetness is likely to have minimized rainfall losses

during the intense precipitation that followed (e.g.

through groundwater and shallow water table recharge),

particularly in the upland catchment.

Flood response

Rainfall

For many environmental studies, it is useful to interpolate

rainfall totals from point gauges as a continuous surface

(Brunsdon et al. 2001). Figure 3 shows spatial coverage of

total precipitation during the 6-day event (30 January–4

February), each raingauge used in the interpolation being

labelled with its total amount recorded over the event.

Using the geographical information system (GIS) package

ARCVIEW, inverse distance weighting analysis was per-

formed on the 6-day event total for each raingauge to

represent precipitation spatially. Inverse distance weight-

ing is based on the assumption that the interpolating

surface should be influenced most by the nearby rain-

gauges and less by the more distant.

The data show inter-site variations in cumulative rain-

fall during the event to be in general related to eleva-

tion, with the highest cumulative totals in the Temple

Sowerby study catchment recorded at the Angerholme

Pots (264.1 mm, elevation=480 m AOD) and Stenners-

keugh (247.4 mm, elevation=380 m AOD) gauges on the

hills in the south of the catchment. There is, however,

exception to this pattern with rainfall potentially under-

estimated at some of the more exposed high elevation

gauges (particularly Lunds Fell: rainfall=186.3 mm,

elevation=650 m AOD) owing to the high winds during

the event. Gusts in excess of 29 m/s (65 miles/h) were

recorded at the Gais Gill AWS (at �400 m AOD) on 2 and

3 February. Associated wind effects may explain discre-

pancies at the Lunds Fell site between recorded rainfall

and elevation relative to other gauges. The predominant

wind direction during the event was south-westerly

(recorded at Gais Gill AWS). This may also explain the

higher rainfall totals in the hills in the south of the

catchment, compared with the hills of similar elevation

in the north that may have experienced some shadow

effect. However, rainfall data from the far north of the

catchment are sparse owing to the location of a large

military training installation on the hills north

of Great Musgrave, which contains only one raingauge

(Warcop).

The lowest 6-day rainfall totals within the study catch-

ment over the same period were recorded at the northerly

gauges Warcop (72.2 mm at 228 m AOD), and Great

Musgrave (82.1 mm at 155 m AOD). Peak daily rainfall

totals during the flood event occurred at all raingauges on

either 31 January or 2 February. The highest daily

0

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Air

tem

per

atu

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Rainfall Air temperature

Fig. 2. Seasonal transitions in rainfall (at War-

cop), air temperature (Warcop), river discharge

(River Eden at Great Musgrave) and soil water

table (Great Musgrave floodplain locations) at

lowland sites in the Upper Eden catchment

(September 2003–February 2004).



(midnight to midnight) totals recorded were again at the

high elevation raingauges in the south of the catchment

at Stennerskeugh (71.9 mm on 2 February) and Anger-

holme Pots (69.6 mm on 2 February). Peak daily rainfall

totals at the lowland raingauges Appleby Mill Hill

(22.9 mm on 31 January) and Brackenber (23.6 mm on

31 January) again highlight the variation in rainfall with

elevation across the catchment.

Data from the dense network of raingauges in the Upper

Eden catchment over this particular multi-day rainfall

event highlight the spatial heterogeneity in rainfall over a

relatively small catchment area. The differences between

cumulative 6-day totals in lowland and upland areas (low-

est value=27.3% of the highest value), and in peak daily

intensities recorded, underlines the necessity for consid-

eration of locations across the full altitudinal range in a

catchment during the installation of raingauge networks.

Table 1 presents return periods [using the Flood Estima-

tion Handbook (Institute of Hydrology 1999)] at selected

raingauges for the both peak daily rainfall and cumulative

totals over the 6-day event. At the high elevation upland

gauges in the south of the catchment (Stennerskeugh and

Angerholme Pots), peak daily rainfall totals recorded on 2

February are of a 4.6–7.4 year return period. At more

sheltered and lower elevation gauges (Gais Gill and Great

Musgrave, respectively), the daily rainfall totals are even

less significant, having a return period of only around 1

year. It is only when cumulative rainfall totals over the 6-

day event are considered that the magnitude of the event

becomes more apparent. Return periods for the 6-day

totals at Angerholme Pots and Stennerskeugh are in excess

of 100 years. Calculated catchment average rainfall values

reinforce the magnitude of the cumulative event, particu-

larly in the uplands, with return periods of 35, 23 and 13

years, respectively, for the Kirkby Stephen, Great Mus-

grave and Temple Sowerby catchments. Multi-day rainfall

events are considered to be an important cause of recent

severe flooding in the UK (Fowler & Kilsby 2003) and it

appears that it is the consecutive days of intense rainfall,

rather than the intensity of individual events that provide

the exceptional feature of this flood event.

Runoff

Figure 4 contrasts the catchment response at the upland

micro-catchment (Gais Gill: Fig. 4a) and lowland mini-

catchment (Blind Beck: Fig. 4b). Comparison is limited to

these micro- and mini-scales as the upland mini-catch-

ment gauge at Ravenstonedale was destroyed by the

floods. The data show preceding discharge at both sites to

be very low and baseflow-dominated. Rainfall is seen to

commence on 29 January, with five distinct peaks of

intense rainfall (with over 2 mm/h of rainfall) passing

over the 7 days to 4 February. The upland micro-catch-

ment exhibits a flashy response, as might be expected for

the steep terrain and largely thin soils, with peak dis-

charge recorded within 4 h of the peak rainfall. The peak-

to-peak lag times for the different flood pulses are seen to

0 10 20 Kilometres

65−100100−125125−150150−200200−300No data

RaingaugesSix-day rainfall total (mm)

65

123 64

72

10058

98

169

229

117 86 7280

13897146

83

8888

84

153127 119

126

175 151

174 247

264 222186

N

66

Fig. 3. Spatial representation of the 6-day precipitation totals for the

Temple Sowerby catchment using inverse distance weighting technique.

Labels indicate the 6-day total for each gauge.

Table 1 Estimated return periods using the Flood Estimation Handbook for daily and 6-day rainfall at selected gauges during the event

Gauge (elevation: m AOD) 6-day total (mm) Return period (years) 1-day maximum (mm) Return period (years)

Great Musgrave (155) 82.1 2.6 25.7 1.0

Gais Gill (400) 174.1 13.4 42.9 1.2

Stennerskeugh (380) 247.4 116 71.9 7.4

Angerholme Pots (480) 264.1 102 69.6 4.6

Catchment average rainfall

Kirkby Stephen 182.5 35 59.2 5.2

Great Musgrave 145.5 23.2 45.0 2.8

Temple Sowerby 118.8 12.9 38.0 2.4



differ markedly for the different flood pulses during the

event. A lag time as short as 15 min was recorded for the

high intensity peak rainfall pulse on 3 February, while

longer lag times of 3:45–4:00 (hr:min) were recorded for

the more isolated, lower intensity rainfall pulses on 1 and

4 February. Flow in the Gais Gill catchment typically

returns to a condition close to pre-flood baseflow between

each rainfall pulse from the second to fifth pulse, high-

lighting the rapid transmission of flow through the catch-

ment.

In contrast to the flashy response in the upland catch-

ment, Blind Beck exhibits the response typical of a low-

land catchment. Figure 4(b) illustrates a more attenuated

response as the lower gradient terrain and deeper soils

lead to a longer travel time of floodwaters through the

catchment. Flow is not observed to return to pre-storm

baseflow conditions in between rainfall pulses, with

much more gradual recession in flows after flood peaks

compared with the Gais Gill hydrograph. The gradual

recession in the Blind Beck hydrograph is particularly

pronounced over the 24 h following the final peak on 4

February. The lowland terrain in the Blind Beck catch-

ment, composed of the floodplain and drumlin field of the

Eden Valley and dominated by livestock farming, is prone

to flooding. Such storage and gradual rise and fall in

levels, typical of the lowland environment, is recorded in

the soil water table records at the adjacent Great Mus-

grave floodplain site (Fig. 4b). A gradual recession in

water table height toward pre-storm conditions is appar-

ent over the 5 days subsequent to the flood (e.g. piezo-

meters GM4.1 and GM4.8). The connection of the

floodplain piezometers to the River Eden is apparent in

the peaks in levels on 31 January and 3 February when

overbank flow occurred. In contrast, water table levels in

the upland catchment at Gais Gill show relatively rapid

drainage fitting with the flashy nature of the catchment.

Water table height in piezometers GGA2 and GGA5 are

seen to return to pre-flood condition within 24 h of the

final rainfall pulse on 4 February (see Fig. 4a). Peak

discharges at both Gais Gill and Blind Beck are seen to

occur on 3 February following a rainfall pulse less intense

than the peak-intensity rainfall pulse that occurred on 31

January. The increased saturation of the catchment fol-

lowing the initial three rainfall pulses is highlighted in the

lowland soil water table records at GM4.1 particularly and

this would have increased the proportion of incident

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vel)Blind Beck Q GM4.1 GM4.8(a) (b)

Fig. 4. (a) Flood response in the Gais Gill upland catchment, showing Gais Gill rainfall, discharge and selected piezometer records GGA2 and GGA5. (b)

Flood response in the Blind Beck lowland catchment, showing Great Musgrave rainfall, Blind Beck discharge and selected piezometer records from the

Great Musgrave floodplain (GM4.1 and GM4.8).



rainfall that contributed to runoff rather than recharge in

subsequent pulses.

Although the return periods of the peak discharge

values at the more recently installed sites cannot be

accurately defined (because of the restricted time series),

estimates of recurrence intervals from the long-term

River Eden gauges using the annual maximum series

(see Flood Estimation Handbook (Institute of Hydrology

1999) for method) with data records of over 14 years at

the Kirkby Stephen gauge, 30 years at Temple Sowerby

and 34 years at Great Corby near Carlisle, suggest an

increasing severity of event with catchment area. At the

Kirkby Stephen gauge, the return period was less than 2

years, at the catchment outlet at Temple Sowerby it was

roughly a 1 in 5-year event and approximately 45 km

downstream of the study catchment at Great Corby

(catchment area 1336.7 km2), the estimated recurrence

interval for the peak flow was in the region of a 1 in 10-

year event.

This increasing severity downstream may reflect the

greater influence of downstream tributaries (River Ea-

mont and River Lowther) which drain the higher eleva-

tion (up to 940 m AOD) Cumbrian Fells to the west of the

Upper Eden. Rainfall in the Upper Eden catchment may

have also experienced a rain-shadow effect from these

Fells, hence the reduced flood severity.

Scale effects

Figure 5(a)–(e) presents a comparison between catch-

ment average rainfall and runoff in a series of nested

catchments from the Gais Gill micro-catchment (area

1.08 km2) up to the catchment outlet at Temple Sowerby

(616.40 km2). Catchment average rainfall was calculated

by the Thiessen polygon approach (Thiessen 1911). Rain-

fall totals for the period 30 January 2004–7 February 2004

at each raingauge were weighted according to the frac-

tions of the catchment they contribute to. These contri-

buting fractions are determined through division of the

catchment into polygons by lines that are equidistant

between pairs of adjacent raingauges.

The resulting rainfall records reinforce the pattern of

increased rainfall with elevation identified in Fig. 3. The

upland catchments (Gais Gill, Artlegarth House) generally

show greater peak rainfall intensities relative to the low-

land locations (Great Musgrave and Temple Sowerby).

Interestingly, the catchment average rainfall for the Scan-

dal Beck catchment at Smardale exhibits peak rainfall

intensities greater than the Gais Gill and Artlegarth House

upland catchments. This is, however, a feature of the

extremely high intensity rainfall at the high elevation

Stennerskeugh gauge that lies outside the Gais Gill catch-

ment but within the catchment of an upland tributary to

the Scandal Beck, thus distorting the catchment average.

Runoff is calculated from the hourly stream discharge

records, which are converted into a total volume of water

expressed as a depth in millimetres over the individual

catchment area. The hydrographs display clear patterns of

attenuation with increasing scale (i.e. the peak runoff

values become less pronounced, but the flood peak takes

longer to travel through a particular location). Peak run-

off at Gais Gill reaches 6.0 mm/h during the largest flood

peak on 3 February, while at the catchment outlet at

Temple Sowerby, the runoff peak for the same pulse was

less than 2.0 mm/h. Translation of the flood peaks is also

clearly apparent in the hydrographs with downstream

propagation of the flood event. Average lag times for the

five flood pulses increase from 2:26 (h:min) at Gais Gill to

3:00 hours at Artlegarth house, 4:40 hours at Smardale,

5:34 hours at Great Musgrave, up to 10:10 hours at the

catchment outlet at Temple Sowerby.

Comparison of the rainfall and runoff totals in the

upstream catchments over the period 30 January 2004–

7 February 2004 shows the erroneous pattern of runoff

exceeding rainfall. Improvements to the calibration of the

rating curves at the upland catchments are a continuing

practice, which may overcome any potential overestima-

tion of runoff. However, the pattern is more likely a

feature of raingauge under-catch in such extreme events

and the limitation of deriving catchment average rainfall

from a solitary raingauge in the Gais Gill/Artlegarth

House catchments. Raingauge under-catch is a process

undergoing ongoing investigation in the Upper Eden with

the deployment of multiple rain and wind gauges along

elevation gradients in the upland catchments. Despite this

potential underestimation of catchment average rainfall,

clear patterns of flood peak attenuation and translation

with catchment scale are apparent downstream of the

upland catchments. Downstream of Artlegarth House,

runoff tends to remain above pre-storm baseflow condi-

tions for the duration of the 6-day event. This is a feature

of the gradient of recession curves after each flood pulse,

which becomes gentler as catchment size increases, so

that the recessions merge into the rising limb of the

subsequent pulse. Such patterns are consistent with the

physical transition in the catchments from the steep

terrain above Artlegarth House to the lowland environ-

ment that becomes more predominant below the settle-

ment of Ravenstonedale. During the period 30 January

2004–7 February 2004, cumulative runoff at the upland

Gais Gill and Artlegarth House catchments is effec-

tively 100% of rainfall, a percentage that diminishes

downstream to between 85 and 93% at Smardale, Great

Musgrave and Temple Sowerby. The shift from the

relatively high contribution of hillslope runoff-driven



channel processes in the upland catchments, character-

ized by steep terrain and thin soils (Gais Gill and Artle-

garth House), to the downstream catchments, where

storage processes become more important (e.g. within-

channel storage, groundwater recharge and storage in

riparian wetlands/ floodplains), is a likely control on such

patterns.

Cumulative runoff records (from 28 January to 9

February; see Fig. 6) from all the monitored catchments

in the Upper Eden highlight the limited extent to which

0

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Rainfall Runoff

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Cum.rain = 193mmCum. run =219mm

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Mea

n c

atch

men

t ra

infa

ll (m

m/h

r)M

ean

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chm

ent

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fall

(mm

/hr)

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atch

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r)

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Ru

no

ff (

mm

/hr)

Ru

no

ff (

mm

/hr)

Ru

no

ff (

mm

/hr)





Rainfall Runoff

Rainfall RunoffRainfall Runoff

Rainfall Runoff

Ru

no

ff (

mm

/hr)

Ru

no

ff (

mm

/hr)

(a) (b)

(d)(c)

(e)

Fig. 5. (a)–(e) Catchment average rainfall rate versus discharge at different scales over

the period 30 January–7 February 2004. (a), Gais Gill; (b), Artlegarth House on Artlegarth

Beck; (c), Smardale on Scandal Beck; (d), Great Musgrave on the River Eden; (e), Temple

Sowerby on the River Eden.



the flashy response in the headwater catchments trans-

lates to the larger downstream catchments. Similarly,

high runoff totals are apparent at Gais Gill and Artlegarth

House between 240 and 250 mm. Significant reductions

in runoff within the nested Scandal Beck catchment

system are apparent at the larger scales between Smardale

(36.58 km2) and Great Musgrave (222.42 km2). The

cumulative runoff totals at Smardale and Great Musgrave

lie between 68 and 75% of the values at the upland

micro-catchments, highlighting the more consistent re-

sponse between the different scales in the lowland envir-

onment. At the catchment outlet at Temple Sowerby, the

reduction in cumulative runoff with scale is further

apparent as total cumulative runoff for the event is only

47% of that at Gais Gill. Relatively high runoff totals are

recorded at the Kirkby Stephen sub-catchment which

drains the main branch of the Eden adjacent to the nested

Scandal Beck system. This reflects the fact that this sub-

catchment recorded the peak recorded rainfall during the

event (Angerholme Pots) and drains the steepest and

highest elevation terrain in the south of the Upper Eden.

Cumulative runoff totals for Blind Beck provide an

interesting mini-scale lowland contrast to the flashy

headwater response. The lower rainfall intensity and the

low gradient of the lowland catchment at Blind Beck

produce a cumulative runoff total similar to the catch-

ment outlet at Temple Sowerby. The clear distinction

between the Blind Beck response and the headwater

response at a similar scale (i.e. between Artlegarth House

and Smardale) highlights the importance of differences in

rainfall alongside the changing balance of hydrological

processes influencing catchment response between the

upland and lowland environments. A transition from the

dominant channel processes in the upland headwaters to

processes of infiltration and storage, which become more

dominant in the lowland environment, alongside lower

gradient topography results in greatly reduced runoff

levels in the lowland catchments.

Future directions

Direct hydrological measurements from nested hydro-

metric networks such as the Upper Eden will provide the

foundation for, and assist validation of, enhanced catch-

ment scale computer simulation models (e.g. SHETRAN,

Ewen et al. 2000). The output from higher resolution

hydrometric data and greater analytical power offered by

hydrological simulations will provide an improved basis

for informing sustainable river basin management in the

predominantly rural catchments that dominate much of

the United Kingdom. As understanding of how the differ-

ent components of the catchment moderate the flood

response improves, flood mitigation measures can be

more effectively formulated. Additionally, these measures

can be more efficiently designed in an environmentally

sensitive manner [e.g. the restoration and reconnection of

riparian washlands to rivers and land drains (English

Nature 2001; Morris et al. 2004)] rather than depending

entirely on engineering structures. The growth in agri-

environment schemes in the UK in recent years [e.g.

Environmentally Sensitive Areas, Countryside Steward-

ship Scheme (Sutherland 2002)] may provide a means for

delivering such approaches as part of integrated catch-

ment-based land management. Numerous workers have

evaluated the varying success of agri-environment

schemes from a nature conservation and biodiversity

perspective (Kleijn et al. 2001; Kleijn & Sutherland 2003;

Vickery et al. 2004). However, there remains a need for

evaluating the hydrological functioning of washlands

restored as part of such schemes. Detailed monitoring

of hydrological response in densely instrumented

catchments such as the Upper Eden may provide the

baseline from which to both design (in terms of the most

effective location of washlands within the river basin) and

evaluate combined catchment land-use and flood man-

agement schemes.

Conclusions

(1) Data from a series of multi-scale catchments during

a 6-day rainfall event have highlighted the importance

of rainfall patterns, scale and antecedent catchment

conditions in controlling channel response in the Upper

Eden.

0

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29Jan

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Cu

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off

(m

m) 249mm

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125mm122mm

Gais Gill (1.08) Artlegarth (2.77)Smardale (36.58) Kirkby Stephen (69.40)Great Musgrave (222.50) Temple Sowerby (616.40)

Blind Beck (9.19)

Fig. 6. Cumulative runoff for different scales and land uses over the

period 28 January–9 February 2004. Catchment areas given in legend (in

km2) and cumulative totals presented at the right of each curve.



(2) Rainfall totals during the 6-day event exceeded 13%

of the annual average totals in the upland environment.

The recorded cumulative rainfall at high elevation

gauges was over three times greater than at lowland

gauges.

(3) Return periods (in excess of 100 years for some

upland raingauges) for the 6-day event suggest that the

cumulative rainfall totals were the exceptional feature of

this flood event.

(4) Spatial disparities in rainfall were a major control

on channel response across the catchment, with up-

land headwaters exhibiting extremely flashy hydro-

graphs with per area runoff totals approximately two

times greater than in lowland catchments of a similar

scale.

(5) The flashy response indicative of the upland head-

waters was not seen to be transmitted far downstream to

the larger catchment scales. At basin sizes above�50 km2,

a more consistent response in terms of total runoff and lag

time was apparent as infiltration and storage processes

become more important.

(6) Further data from intermediate scales (�10 km2)

between the upland/lowland transition would be desir-

able to assess the changing influence of channel and

storage processes on catchment response at differing

scales. Future data from the expanding hydrometric net-

works in the CHASM experimental catchments offer

scope for such elucidation.

(7) The improved understanding of hydrological re-

sponse over a range of scales offered by densely instru-

mented river basins can be used to underpin sustainable

catchment management and land use strategies.

Acknowledgements

Jane Atkins at the Environment Agency (Penrith) is

thanked for supplying some of the rainfall and river flow

records. The CHASM project was funded by the Wellcome

Trust and administered by the Natural Environment

Research Council through the Joint Infrastructure Fund.

The many landowners of the Upper Eden who have

facilitated the installation and access to the extensive

network of instrumentation are also thanked.

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Monitoring a flood event in a densely instrumented catchment, the Upper Eden, Cumbria, UK

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