Assessing damaged road verges as a suspended sediment source in the Hampshire Avon catchment, southern United Kingdom

Abstract

Abstract:Diffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub-catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time-integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub-catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub-catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02-27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 š 3%, 4 š 2% and 20 š 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub-catchment were as high as 33 š 2%. Reconstruction of historical sources in the same sub-catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15-20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources.

Ascribing soil erosion types for sediment yield using composite fingerprinting technique

“…This level of uncertainty confirms that the optimized mixing model provides an acceptable prediction of the fingerprint property concentrations associated with sediment samples and lies within ranges reported by Walling et al (2006), Minella et al (2008) and Collins et al (2010c). High inputs from sheet erosion are consistent with susceptible soil; fine grained particles, poor vegetation and a large area promote relatively high sediment yields.…”

“…20 sheet erosion samples and 15 representative samples each from the rill and gully erosion areas. The samples were taken from depths of 0-2 cm (Walling and Woodward 1995, Collins and Walling 2002, Collins et al 2010a, 2010b, 2010c, 2-30 cm and >30 cm (Gruszowski et al 2003) for sheet, rill and gully erosion, respectively. Furthermore, six samples were collected from deposited materials at the outlet of the watershed.…”

“…Accordingly, rill and gully erosion sampling sections were limited to active erosion scars (Collins et al 1997b, Juracek andZiegler 2009). A range of locations was ultimately sampled within the watershed to represent areas with good connectivity to the watercourse system (Walling et al 2006, Collins et al 2010c, 2010d. All samples were collected using a stainless steel trowel that was regularly cleaned to avoid intersample contamination (Collins and Walling 2002).…”

Evaluating the importance of surface soil contributions to reservoir sediment in alpine environments: a combined modelling and fingerprinting approach in the Posets-Maladeta Natural Park

“…However, source fingerprinting techniques continue to be most widely applied in agricultural and forest catchments (e.g. Owens et al, 2000;Collins et al, 2010;Martínez-Carreras et al, 2010b;Blake et al, 2012;Schuller et al 2013) and the opportunity in alpine catchments remains unexploited.…”

Análise qualitativa e quantitativa da histerese entre vazão e concentração de sedimentos durante eventos hidrológicos

“…Este complexo mecanismo de transferência depende, além das características da precipitação, do centro de massa das áreas que geram o escoamento e sedimentos (Klein, 1984), e da sua natureza (uso, manejo, relevo). É importante salientar que a Q e a CSS também sofrem influência direta dos processos de ligação entre calha e vertente e da variabilidade temporal das fontes de sedimentos que, por sua vez, está intimamente relacionada com as características da precipitação (Collins et al, 2010;Minella et al, 2007;2008;Walling, 2005). O comportamento dos sedimentos suspensos nos rios é função, também, das condições de energia do escoamento superficial e da disponibilidade de energia para o seu transporte.…”