Fluvial sediment budget of a Mediterranean river: the lower Tordera (Catalan Coastal Ranges, NE Spain)

Abstract The lower Tordera River is a representative case of water and sediment dynamics and uses in a large river in the Western Mediterranean region. Along the study reach, the fluvial regime of the river changes, shifting from a perennial water and sediment circulation in the upper parts to an ephemeral flow pattern in the lower sections. The fluvial sediment budget of the lower Tordera was estimated based on field measurements of suspended and bedload and a survey of cross-sections. Field data were obtained between January 1997 and June 1999, a period that was dryer than the average. Most sediment is transported as bedload (more than 3/4 of the total load), both at the entrance section of the river reach and at the outlet section, close to the Mediterranean Sea. A total of 156,700 tonnes of sediment (62,680 tonnes/year) entered the system, mostly during discharges below bankfull, while 107,000 tonnes (42,800 tonnes/year) were exported to the sea, almost exclusively during floods. The net accumulation of sediment was 14,600 tonnes per year (as bedload), especially during the dry years of 1998 and 1999, when small floods circulated through the upper sections but did not reach the lowermost part of the river. As a consequence, a mean aggradation of the riverbed of around 6.8 mm/year has occurred, a figure that has been corroborated after the analysis of a series of cross-sections. Residence time of sediment in the perennial reach, calculated at a long-term, ranges from 6 years for sediments in the active base flow channel to 164 years for sediment placed above bankfull level, which is only entrained during high flows. Residence time of sediment in the ephemeral reach, calculated for the period 1997–1999, is only slightly higher than that of the perennial part of the river. This fact can be related to the current adjustment of the river system to historical mining. The riverbed is slowly adjusting to the new conditions, and important sedimentation is taking place in many upstream sections, while erosion still occurs in the lowermost reaches, thus causing the relatively low residence time of sediment.

[1]  David R. Maidment,et al.  Handbook of Hydrology , 1993 .

[2]  T. Dunne,et al.  Sediment Production From Forest Road Surfaces , 1984 .

[3]  M. Church,et al.  The sediment budget in severely disturbed watersheds, Queen Charlotte Ranges, British Columbia , 1986 .

[4]  M. Inbar,et al.  Rates of fluvial erosion in basins with a Mediterranean type climate , 1992 .

[5]  Trimble,et al.  Contribution of stream channel erosion to sediment yield from an urbanizing watershed , 1997, Science.

[6]  M. Church,et al.  Bed‐material transport estimated from channel surveys: Vedder River, British Columbia , 1995 .

[7]  R. Moore,et al.  Production, storage and output of coarse upland sediments: natural and artificial influences as revealed by research catchment studies , 1986, Journal of the Geological Society.

[8]  H. Slaymaker.  Patterns of Present Sub-Aerial Erosion and Landforms in Mid-Wales , 1972 .

[9]  E. Andrews.  Effective and bankfull discharges of streams in the Yampa River basin, Colorado and Wyoming , 1980 .

[10]  G. Pickup,et al.  Effects of hydrologic regime on magnitude and frequency of dominant discharge , 1976 .

[11]  R. H. Kesel,et al.  An approximation of the sediment budget of the lower mississippi river prior to major human modification , 1992 .

[12]  Peter C. Klingeman,et al.  Gravel-bed rivers in the environment , 1998 .

[13]  F. Kilpatrick,et al.  Channel geometry of Piedmont streams as related to frequency of floods , 1964 .

[14]  C. Kroll.  Estimate of sediment discharges, Santa Ana River at Santa Ana and Santa Maria River at Guadalupe, California , 1975 .

[15]  D. Thomas,et al.  A DEFINITION OF DOMINANT DISCHARGE , 1966 .

[16]  S. Schumm.  The shape of alluvial channels in relation to sediment type , 1960 .

[17]  Roland H. Lamberson,et al.  Stochastic model for the long‐term transport of stored sediment in a river channel , 1987 .

[18]  Chris Paola,et al.  Bias and precision of percentiles of bulk grain size distributions , 1997 .

[19]  Richard D. Hey,et al.  Sediment transport in gravel-bed rivers , 1987 .

[20]  D. Inman,et al.  Climate Change and the Episodicity of Sediment Flux of Small California Rivers , 1999, The Journal of Geology.

[21]  Anders Rapp,et al.  Recent Development of Mountain Slopes in Kärkevagge and Surroundings, Northern Scandinavia , 1960 .

[22]  Rhea P. Williams.  Sediment discharge in the Santa Clara River Basin, Ventura and Los Angeles Counties, California , 1979 .

[23]  M. Church,et al.  Sediment transport along lower Fraser River: 2. Estimates based on the long‐term gravel budget , 1999 .

[24]  A. Schick,et al.  AN EVALUATION OF TWO TEN-YEAR SEDIMENT BUDGETS, NAHAL YAEL, ISRAEL , 1993 .

[25]  D. Walling,et al.  Erosion and sediment yield: a global overview , 1996 .

[26]  Thomas E. Lisle,et al.  Bankfull discharge and sediment transport in northwestern California , 1987 .