River channel changes through time and across space: Using three commonly available information sources to support river understanding and management in a national park

Abstract

In river landscapes subject to prolonged and high population pressure, the impact of human actions is usually so pervasive that re-establishment of 'natural' river conditions is not possible. However, understanding the impacts of humans on river ecosystems is essential to identify how degradation of condition may be slowed or reversed and may also lead to the recognition that some human activities may be crucial for maintaining highly valued and sensitive river ecosystems. To achieve the necessary understanding for such judgements, it is essential to assemble, synthesize and analyse information on human actions, river environments and their interactions. In this paper, we focus on three commonly available information sources (historical records/ archives, topographic and geomorphological maps, river habitat surveys) that can deliver relevant information over three timescales (centuries, decades, years). We illustrate the potential of these three data sources to assemble thematic and quantitative knowledge about how river systems function under a history of different human pressures and interventions, by exploring an example river landscape: the New Forest, southern England. We use this illustrative example for three reasons.First, for more than 1000 years, the New Forest has been affected by a complex range of land use and management practices which have heavily influenced the contemporary river landscape. Second, many of these human actions have degraded the landscape but others sustain highly valued landscape characteristics and ecosystems.Understanding the relative negative and positive impacts of different human actions is essential to understanding any river landscape with a long history of human use, and thus to designing balanced and appropriate management approaches. Third, in this special issue in memory of Professor Ken Gregory, we focus on an example landscape where he conducted research, allowing us to incorporate insights and data from his observations.geomorphological mapping, historical sources, human impacts, river habitat survey, river monitoring design, river processes, time and space scales | INTRODUCTIONRiver landscapes within Europe, as in many other areas of the world, have long been modified by both direct and indirect human actions. The resultant impacts are most deep-seated in areas of prolonged, high population density. In such areas it is not possible to restore rivers to a pre-impact, 'natural' condition, but it may be possible to slow or reverse degradation and to improve river functioning and condition (Brierley & Fryirs, 2008;Dufour & Piégay, 2009). The term 'restoration' can still be applied in its widest sense to refer to all activities that assist the recovery of river ecosystems that have been degraded, damaged or destroyed

Trees, large wood and streams: Using archive survey data to inform changing interactions in a human‐impacted landscape

“…The heath‐scrub‐lawn‐mire vector opposes the sinuosity vector (i.e., it is associated with low sinuosity streams), whereas the deciduous woodland vector plots close to the sinuosity vector (i.e., is associated with more sinuous streams) (Figure 4a). This follows observations by Gurnell and Hill (2021) that streams are less likely to be modified in the Open Forest, but, small, unmanaged, heath‐scrub‐lawn‐mire streams tend to be less sinuous than those flowing through Open Forest woodland. Within the analysed data set, streams bordered by heath‐scrub‐lawn‐mire were frequently headwater streams, explaining the inverse relationship between this cover type and distance from source (Figure 4b).…”

“…The study area within the New Forest, southern England, is the second most densely populated National Park in England after the South Downs (63 people per km 2 ). Gurnell and Hill (2021) reviewed the landscape character and management of the New Forest that is relevant to its stream systems. We summarise their findings in this section.…”

“…We revisit a walkover survey of ~66 km of streams conducted in 1991, which was previously analysed by Gregory et al (1993) to identify spatial patterns in the load of large wood (kg.m −2 channel area) retained in the streams. The 1991 survey has not been repeated in full in subsequent years, but as an example of the potential information that could be revealed from analysis of repeat surveys, we have extracted the same set of variables collected in 1991 from surveys of ~10 km of the Highland Water undertaken in 1997 and 2021 (Gurnell & Hill, 2021). The straightforward nature of the surveys allows us to consider the potential of additional surveys being repeated by river scientists as well as by volunteers (‘citizen scientists’) following appropriate training.…”

“…Recently, Gurnell and Hill (2021) presented a multi-scale investigation of the legacy effects of human activities on stream environments in the New Forest, southern England. Their study revealed both positive and negative impacts of humans on this sensitive, predominantly wooded landscape, which has been subject to a variety of land and river management practices for over 1000 years.…”

Professor Kenneth John Gregory (1938–2020): The career, contributions and legacy of an eminent geographer and fluvial geomorphologist

“…One morphological legacy of human action is that small, modified channels are now 2.5-3.3 times deeper than their non-modified equivalents, a result that is highly significant when trying to restore such channels. Gurnell and Hill (2022) 'complex response' model of terrace formation, which was developed from stream table experimentation. In the Cretan catchments, the number and age of channel incision and aggradation phases were similar in both uplifted and non-uplifted catchments, indicating that river responses following uplift have not followed complex response trajectories, at least not in the form envisaged by Schumm and Parker (1973).…”