UPPER MIMRAM VALLEY summary assessment evaluation guidelines area36

County map showing location of LANDSCAPE CHARACTER AREA Stevenage

Scale 1:500,000 Bishops Stortford

Hertford

Hemel Hatfield Hempstead St Albans

Watford area 36

LOCATION KEY CHARACTERISTICS The Mimram valley between Digswell Water and • wetland vegetation screens river from view, so not major feature within the landscape LANDSCAPE CHARACTER • parkland aspects, especially around Lockleys school River valley intertwined with modern road network and (waterfall) partly confined by housing development. Similar in character to the river valley to the east, but with stronger DISTINCTIVE FEATURES urban influence • • impact of roads and housing

Mimram Valley aerial view • from Digswell Viaduct (HCC Landscape Unit)

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PHYSICAL INFLUENCES HISTORICAL AND CULTURAL INFLUENCES Geology and soils. Stoneless mainly calcareous clay soils The Digswell Viaduct is apparent at the eastern end of this over river alluvium (Thames series) area, as is the 17.5 acres of ornamental parkland now run Topography. Shallow south-facing slope of river valley by a local society. It comprises woodland and ornamental Degree of slope. 1 in 7 on steepest valley slopes, with as trees around a small lake, made in 1810 as part of Digswell fall of 1 in 1500 along this reach of the river House Park. It is marred by the noise of the nearby A1000 Altitude range. 61m to72m and A1(M). The western section of this area lies within the Hydrology. The Mimram is a relatively fast-flowing, gravel- parkland around what is now Lockleys School. bedded chalk stream within a mainly rural catchment. The Field pattern. There is no apparent field pattern in this water quality is suitable for species such as trout and area, due to current and historic land use as amenity, grayling and the dominant species is the brown trout, pasture and parkland. although sections upstream of Digswell have been dry in Transport pattern. The river valley in this area is contained recent years. In some sections terrestrial vegetation has by the road network, with the A1000 weaving across the taken over from aquatic, but channel improvements have river and a continuation of the B1000 forming a boundary been carried out at Digswell and Whitwell to prevent to Digswell village. The river disappears beneath the A1(M) impoundment and remove accumulated silt. The riverbanks but is a notable feature within old Welwyn village. are mostly less than 1m high, with good shallow margins Settlements and built form. This section of the river valley and varied marginal flora. is confined by the southern edge of Digswell and mid-20th Land cover and land use. Mainly pastoral, with extensive century development within Digswell Park, now part of the wetland vegetation. development of . Digswell Viaduct was Vegetation and wildlife. Mainly willow and alder, which built in the late 1840s to carry the new railway, out of make a significant contribution to the local landscape. There bricks manufactured on site. It is a Grade II listed structure is some classic riverside pasture with limited improvement. 450m long and 25m high, with 40 arches. Originally built The more interesting areas for wildlife are the riverside of red brick, it was refaced with blue engineering bricks in margins and damp areas. 1935.

pg 156 South Hertfordshire Landscape Character Assessment UPPER MIMRAM VALLEY summary assessment evaluation guidelines area 36

VISUAL AND SENSORY PERCEPTION ACCESSIBILITY The overall parkland character of this area has been masked Footpath from Digswell, otherwise quite inaccessible, by 20th-century development, in particular the road especially the western section. There is unrestricted access network, which has destroyed its former tranquillity and to the parkland around Digswell Lake for memebrs of the adds constant noise to the intermittent rush of trains over Digswell Lake Society. Digswell Viaduct. It is a rather confined area, with a sense of offering a retreat from its urban surroundings. COMMUNITY VIEWS Rarity and distinctiveness. There are several unusual This area includes some valued elements (D). features in this area . Digswell Viaduct is ‘probably the most widely recognisable structure in the county’ (Landscape Strategy Vol.1)

VISUAL IMPACT Some people find the Viaduct is gloomy and oppressive, as well as impressive, but is matched for impact by the road network around it.

CONDITION ROBUSTNESS Land cover change: localised Impact of landform: apparent Age structure of tree cover: mixed Impact of land cover: prominent Extent of semi-natural habitat survival: fragmented Impact of historic pattern: interrupted/relic Management of semi-natural habitat: not obvious Visibility from outside: locally visible Survival of cultural pattern: declining Sense of enclosure: confined Impact of built development: high Visual unity: incoherent Impact of land-use change: moderate Distinctiveness/rarity: unusual

Strengthen Conserve Safeguard and and and reinforce strengthen manage

Improve Improve Conserve and and and reinforce conserve restore MODERATE

CONDITION Restore Improve condition Reconstruct and to maintain POORrestore GOOD character

WEAK MODERATE STRONG

ROBUSTNESS

South Hertfordshire Landscape Character Assessment pg 157 UPPER MIMRAM VALLEY summary assessment evaluation guidelines area 36

STRATEGY AND GUIDELINES FOR MANAGING CHANGE: IMPROVE AND REINFORCE • promote the value of biodiversity and the use of locally native species • promote the maintenance of semi-natural habitats along the river, with buffer zones where necessary to prevent agricultural run-off • encourage the retention of ditches running into the river • promote the maintenance of pasture within the river valley • promote the planting of trees as a buffer between rural and urban zones in this area, to provide visual and noise screening and to absorb pollution from road traffic. • encourage the use of native species in rural areas and the retention of ornamental and semi-ornamental species for urban situations • promote an increase in public access to the river, especially from the urban areas • ensure that the value of veteran trees and dead wood is fully recognised and that appropriate management techniques are implemented and maintained • encourage a diversification of mowing regimes in areas of open space, to increase biodiversity, create visual interest and reduce maintenance costs • manage ponds and lakes so as to avoid enriching habitats with debris • avoid damage to riverbanks and over-widening of the open water channel as a result of agricultural or other practices • do not c lear vegetation from river bank, but retain shrubby vegetation, where there is no conflict with public rights of way, for perching and nesting. • should a second viaduct be constructed near the existing Digswell Viaduct, care should be taken to ensure that the design of the new structure is informed by the proximity and style of the existing. Should lighting of either structure be considered, care should be taken to ensure that bat colonies are not disturbed. Consideration could be given to low-UV lighting to highlight this notable local landmark.

• Digswell Viaduct with grazing meadow (HCC Landscape Unit)

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