Effect of seasonal snow cover on suspended sediment runoff in a mountainous catchment

doi:10.1016/j.jhydrol.2012.01.029

Journal of Hydrology

Volumes 428–429, 27 March 2012, Pages 116-128

https://doi.org/10.1016/j.jhydrol.2012.01.029 Get rights and content

Summary

The effect of snow cover and snowmelt on suspended sediment (SS) runoff at a mountainous catchment in the temperate zone was investigated. The observation was carried out from March 1999 to May 2002 (3 years) at an experimental catchment with the area of 0.347 km² ranging from 280 m to 618 m above mean sea level with average stream gradient of 1/4. It was concluded that the snow accumulation and ablation process in the catchment had a significant impact on SS runoff characteristics especially during the snow-melting period. It was estimated that more than 60% of the annual SS load flowed out during the snow-melting period because of the enhanced water discharge. The daily average SS flux during the snow-melting period was calculated to be 2.54 g s⁻¹ km⁻², corresponding to a 6–7 times greater SS flux than that during other periods. The C–Q relation analysis in each runoff event revealed a dynamic change in the SS runoff mechanism during the snow-melting period. Strong clockwise hysteresis in C–Q relation in the early stage of the snow-melting period may be explained by consumption of the bed load by the first flush followed by quick depletion of the material on the stream bed due to suppression of further SS supply by thick snow cover. Counterclockwise hysteresis in C–Q relation was observed only in the late stage of the snow-melting period. SS production at steep slopes beside the stream by avalanches and surface soil slides, induced by an abundance of meltwater, was considered to be one of the main causes of the counterclockwise loops. It would be hypothesized that exposure of other steep slopes or bluffs in the catchment apart from the stream and stream bank failure by repeating surges of the stream water stage could also be other possible SS sources causing counterclockwise hysteresis in the late snow-melting period.

Highlights

► Effects of snow cover on SS runoff at a temperate mountainous area were studied. ► Snow accumulation and ablation had a significant impact on SS runoff. ► SS runoff mechanism variation within the snow-melting period was revealed. ► Thick snow cover caused strong clockwise CQ hysteresis in the early melting period. ► Counterclockwise CQ hysteresis was observed only in the late snow-melting period.

Introduction

Suspended sediment (SS) loads from mountainous headwaters have considerable influence upon geomorphology in downstream reaches. Long term changes in the river bed level and particle size distribution of the bed are strongly affected by provision of SS loads (Zabaleta et al., 2007). Runoff with high turbidity and associated SS has significant implications for aquatic ecology as well, because it directly causes light suppression and alteration of BOD levels leading to considerable impact on aquatic macroinvertebrate communities (Lawler et al., 2006). Walters et al. (2003) pointed out that higher baseflow turbidity and finer beds could inhibit spawning activities of endemic fish species and favor homogenization of fish assemblages, thereby representing a serious threat to global biodiversity.

As summarized by Williams (1989), the timing and amount of SS and runoff water arriving at a specific observation point are affected by various factors including precipitation intensity and areal distribution, runoff amount and rates, floodwater travel rates and distances, spatial and temporal storage–mobilization–depletion processes of available sediment, and sediment travel rates and distances. Numerous studies have estimated SS flux at specific downstream points and have evaluated the contribution of each SS source in a watershed to show various sediment sources, e.g. stream banks (Lefrancois et al., 2007), unsealed roads (Motha et al., 2003), and landslides (Schwab et al., 2007). Attempts have also been made to elucidate the SS production mechanism from various angles (Dapporto et al., 2003, Rinaldi et al., 2004, Greer et al., 2006, Schmidt and Morche, 2006, Ide et al., 2009).

In addition to these factors, catchment hydrology is strongly governed by snow cover staying on the ground in snow-covered areas (Singh and Singh, 2001, Pomeroy and Brun, 2001, Bales et al., 2006, Whitaker et al., 2008). Snow accumulation and ablation processes considerably affect stream water quality as well as water runoff (Tranter and Jones, 2001, Woli et al., 2008).

Areas seasonally covered by snow are among the most sensitive areas to the recent climate change induced by global warming (Singh and Bengtsson, 2004, Barnett et al., 2005, Stewart, 2009). Lemke et al. (2007) reported that, over the period from 1922 to 2005, the linear trend in the March and April snow-covered area in the northern hemisphere was a statistically significant reduction of 7.5 ± 3.5%. With projections of further warming, the duration of snow cover is predicted to be shortened with earlier snowmelt in spring (Singh and Bengtsson, 2005, Lopez-Moreno et al., 2008, Scheurer et al., 2009).

The earlier snowmelt results in earlier exposure of land surfaces susceptible to erosion by surface runoff. Moreover, warmer air temperatures alter snowfall to rainfall. The surface runoff caused by the direct rainfall on the exposed land surface must transport more sediment to streams than meltwater runoff traveling through snowpack or underlying soil. In light of the prediction of further global warming, precise understanding of the effect of snow cover on the SS runoff mechanism is a pressing urgent need.

With regard to the effects of snow and ice on SS runoff, a number of field observations on catchment scales were carried out in arctic regions (Hodson et al., 1998, Cockburn and Lamoureux, 2008, McDonald and Lamoureux, 2009) and glaciers (Orwin and Smart, 2004, Singh et al., 2005) to elucidate sediment production mechanisms. However, only few attempts have so far been made in temperate snowy catchments during the snow accumulating and melting period (Kurashige, 1998, Lenzi and Marchi, 2000, Lenzi et al., 2003, Langlois et al., 2005). Because snow in the temperate zone is especially vulnerable to the recent global warming (Brown et al., 2007), it is important to quantitatively evaluate the effect of snow cover on SS runoff in temperate snowy catchments in order to develop precise models representing SS runoff in the temperate zone.

In order to investigate the effect of snow accumulation and ablation on SS runoff characteristics, an intensive field observation at an experimental catchment in a temperate snowy region was conducted during the period spanning both the snowy season and the season without snow cover. The seasonal changes in SS runoff were presented on the basis of the observed data. The changes in the SS concentration (SSC) with respect to the changes in the water discharge in each hydrological event, i.e. C–Q hysteresis, were analyzed in detail. The changing effect of snow cover to SS runoff along with the snow-melting stage was discussed to propose new insights into SS runoff during the snow-melting period.

The present study will provide useful information for precise estimation of SS flux in a temperate snowy basin. Applying the information obtained in the present study to the previously proposed SS runoff models will be valuable for improvement of the representativeness of existing models in a temperate snowy basin.

Section snippets

Site description

The most upstream portion of a stream in the University Forest of Yamagata University (38°33′N, 139°52′E), which is located in the coastal region along the Japan Sea in northern part of Honshu, the main island of Japan, was designated as the experimental catchment for the present study (Fig. 1).

The coastal region along the Japan Sea in northern Japan has a considerable amount of snowfall in the winter despite the fact that the region is situated in the temperate zone with a low altitude. The

Changes in precipitation and accumulated snow condition

The changes in the observed daily precipitation and the snow depth at the meteorological observation point (Fig. 2 (top)) during the whole observation period are shown in Fig. 3a. Snowfall started in November and the precipitation was enhanced with fewer dry spells in the winter. Snowpack started to cover the ground continuously in the middle of December and continued to stay until late April or the beginning of May. The snow depth reached its annual maximum as much as 3 m in February. Iida et

Seasonal variation in SS runoff

During the no-snow period, the SS runoff from the experimental catchment presented typical characteristics of a forested mountainous catchment without snow. SSC stayed low at around 1–5 mg/L while the discharge was at base flow. Occasional high SSC peaks were brought about by rainfall events with clockwise hysteresis loops in the C–Q relation. During the snow-accumulating period, discharge peaks were lower and more infrequent than during other sub-periods, resulting in small sporadic SSC peaks

Conclusions

To investigate the effect of seasonal snow cover on SS runoff, an intensive field observation was conducted at a mountainous catchment (0.347 km²) in the temperate zone, which is characterized by temperate climate in the summer and thick snow cover in the winter.

The L–Q relation for each sub-period, namely the no-snow period, the snow-accumulating period and the snow-melting period, was represented by a conventional power function. The obtained parameters indicated that the SS load relative to

Acknowledgements

This study was supported in part by Japan Society for the Promotion of Science through Grant-in-Aid for Young Scientists (B) #15780155. The authors are grateful to Mr. Masashi Sato for his field observation and data handling. Special thanks are due to the staff members of the University Forest of Yamagata University for their assistance in the field observation.

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Effect of seasonal snow cover on suspended sediment runoff in a mountainous catchment

Summary

Highlights

Introduction

Section snippets

Site description

Changes in precipitation and accumulated snow condition

Seasonal variation in SS runoff

Conclusions

Acknowledgements

Forest Ecol. Manag.

J. Hydrol.

Catena

Catena

Sci. Total Environ.

Catena

Geomorphology

Global Planet. Change

Geomorphology

J. Hydrol.

Geomorphology

J. Hydrol.

J. Hydrol.

Catena

Weirs and Flumes for Flow Measurement

Mountain hydrology of the western United States

Water Resour. Res.

Potential impacts of a warming climate on water availability in snow-dominated regions

Nature

Turbidity and suspended sediment dynamics in small catchments in the Nepal Middle Hills

Hydrol. Process.

Vulnerability of alpine stream biodiversity to shrinking glaciers and snowpacks

Global Change Biol.

Hydroclimate controls over seasonal sediment yield in two adjacent high arctic watersheds

Hydrol. Process.

Mechanisms of riverbank failure along the Arno river, central Italy

Earth Surf. Proc. Land.

Sediment fingerprinting: review of the method and future improvements for allocating nonpoint source pollution

J. Environ. Eng. ASCE

WEPP simulation of observed winter runoff and erosion in the US Pacific Northwest

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Sediment sources and transport pathways in a rural catchment, Herefordshire, UK

Hydrol. Process.