Lower Ebro Research Articles

Sediment transport in a highly regulated fluvial system during two consecutive floods (lower Ebro River, NE Iberian Peninsula)

AbstractThe transfer of sediment through a highly regulated large fluvial system (lower Ebro River) was analysed during two consecutive floods by means of sediment sampling. Suspended sediment and bedload transport were measured upstream and downstream of large reservoirs. The dams substantially altered flood timing, particularly the peaks, which were advanced downstream from the dams for flood control purposes. The suspended sediment yield upstream from the dams was 1 700 000 tonnes, which represented nearly 99 per cent of the total solid yield. The mean concentrations were close to 0·5 g l−1. The sediment yield downstream from the dams was an order of magnitude lower (173 000 tonnes), showing a mean concentration of 0·05 g l−1. The dams captured up to 95 per cent of the fine sediment carried in suspension in the river channel, preventing it from reaching the lowermost reaches of the river and the delta plain. Total bedload transport upstream from the dams was estimated to be about 25 000 tonnes, only 1·5 per cent of the total load. The median bedload rate was 100 gms−1. Below the dams, the river carried 178 000 tonnes, around 51 per cent of the total load, at a mean rate of 250 g ms−1. The results of sediment transport upstream and downstream from the large dams illustrate the magnitude of the sediment deficit in the lower Ebro River. The river mobilized a total of 350 000 tonnes in the downstream reaches, which were not replaced by sediment from upstream. Therefore, sediment was necessarily entrained from the riverbed and channel banks, causing a mean incision of 33 mm over the 27 km long study reach, altogether a significant step towards the long‐term degradation of the lower Ebro River. Copyright © 2005 John Wiley & Sons, Ltd.

The environmental impact of the Spanish national hydrological plan on the lower Ebro river and delta

The main goal of the Spanish National Hydrological Plan is the implementation of an inter-basin water transfer of a maximum of 1050 hm 3 /year from the lower Ebro River to the north and south Mediterranean coast. The plan also includes an additional list of public works of about 100 new dams and the infrastructure for new irrigation areas, as well as water treatment plants and river canalizations, etc. Taking into accout that the planned Ebro transfer would take 50 m 3 /s during 8 months, and that river flow is mostly in the interval of 150-250 m 3 /s during this period, the abstraction would repesent between one-third and one-fifth of the Ebro flow. This plan, if implemented, would have a strong negative environmental impact on the fluvial ecosystem, as well as on the estuarine and marine ecosystems, but these impacts have not been properly considered in the environmental assessment. This paper principally deals with the environmental effects of the water transfer on the area that supplies the water, downstream from the diversion point. The impact of an inter-basin water transfer on the mouth area is based on three aspects: (1) there is an increase in salinity in the delta and estuary; (2) there is a decrease in the biological productivity, mostly due to the decrease of nutrient inputs, and there are also changes in the species distribution; and (3) the river carries less sediment, which affects the geomorphology of the system. The possible effects of lower water quality and changes in the fluvial system have also to be considered. The sustainability of deltas can only be guaranteed with the allocation of an appropriate flow regime, which must include not only a liquid flow, but also a solid flow (sediment), given that deltas and coastal systems need sediment inputs (and nutrients) from the river to maintain their structure and dynamics. The classical methods of determining environmental flows in rivers are neither designed nor adequate for the objective of maintaining the deltas and estuaries in a good ecological state. The determination and implementation of an environmental flow regime not only for the river but also for the coastal and marine systems represent a new challenge for scientists and managers.

Land requirements for Pinus halepensis Mill. growth in a plantation in Huesca, Spain

Abstract. Land requirements for Pinus halepensis Mill. growth were studied in thirty plots of a 40 year‐old plantation in the semiarid Lower Ebro valley, northeast Spain, by comparing site index values to land characteristics. Site index at 40 years ranges from 4.1 m to 12.3 m. Moisture availability is the basic requirement for growth while nutrient availability has only a minor influence. Changes in moisture availability in the area are controlled by changes in soil rootable depth, with a minor effect of aspect. Soils developed on Tertiary gypsum rock are not suitable for afforestation with this species. Geomorphic and soil information may be combined, at various degrees of detail, to provide reliable estimates of Aleppo pine growth.

A historical perspective of the morphological evolution in the lower Ebro river

The morphological evolution, hydrodynamics and sediment dynamics of the lower Ebro are studied from historical and current data in order to determine the main changes that have governed the evolution of the Ebro channel near the river mouth during the last few centuries. The evolution of the mouth of this river during the last 2000-years, from an estuary to a delta, is interpreted as a process that has been accelerated by human land management. However, an inverse trend has been observed during recent decades: (1) the river mouth has been affected by erosion due to a drastic decrease in the river sediment discharge, and (2) the lower Ebro tends to evolve towards a quasi-permanent salt-wedge estuary as a consequence of the decrease in the river water discharge. Freshwater and sediment discharge decreases are mainly related to intense river water management during this century. The salt wedge favours erosion in the river banks, widening the river channel and causing an aggradational trend in the lower Ebro. Accretion-erosion rates and the sediment budget in the river mouth are estimated for different conditions.

Changes in the hydrology and sediment transport produced by large dams on the lower Ebro river and its estuary

The mean annual flow of the lower Ebro river has reduced by 29% during this century (592 to 426 m3 s−1). The main causes are increased water use and evaporation from reservoirs in the river basin. The losses due to irrigation explain 74% of the decrease, whereas losses by evaporation in the reservoirs explain another 22%. Decreased flow in the lower Ebro river caused an increase in the salt wedge in the estuary. During the study period, the permanent low river flows from July 1988 to April 1990 caused the continuous presence of the salt wedge for 18 months. Historical data for sediment transport in the Ebro river are scarce and incomplete. Limited data before the construction of reservoirs in the Ebro basin allow only an estimate of the order of magnitude of annual suspended sediment transport (3·0 × 107 Mt yr−1). Before the construction of large reservoirs in the lower Ebro at the end of the 1960s, the sediment transport was estimated to be around 1·0 × 107 Mt yr−1. This amount was reduced to around 0·3 × 106 Mt yr−1 after construction of the dam. Currently, this amount ranges from 0·1 to 0·2 × 106 Mt yr−1, which represents a reduction of more than 99% in sediment transport. On a seasonal scale, the effects of the dams have been the standardization of the river flow and the virtual suppression of peaks in sediment transport. In the estuary, the salt wedge dynamics changed and its presence increased. River regulation and hydropower generation also changed the hydrology of the river on a daily scale. The effect of local storms on the river flow and the sediment transport has been suppressed. At present, these changes are related to hydropower generation.

Changes in the hydrology and sediment transport produced by large dams on the lower Ebro river and its estuary

Changes in the hydrology and sediment transport produced by large dams on the lower Ebro river and its estuary

Macroinvertebrate community in the lower Ebro river (NE Spain)

We examine the macroinvertebrate community composition and dynamics in the last 60 km of the Ebro river (NE Spain). Different sampling methods (individual stones, Surber, kick samplers and artificial substrate) were used depending on the characteristics of the sites chosen (substrate, current velocity, saline influence). The high nutrient content and the abundance of UFPOM is the origin of a high density in stones although no clear pattern exists between stone surface area and density or species richness. The high spatial heterogeneity and moderate disturbance intensity and frequency because of river regulation explains the relatively rich macroinvertebrate community and the low temporal changes in the community.

Effects of river regulation on the lower Ebro river (NE Spain)

AbstractThe regulation of the Ebro River in the 1960s has changed the discharge pattern: spring floods have been reduced and, as the reservoirs are used for hydroelectrical purposes, discharge varies daily.The last 50 km of the river have been studied for two years (1986 and 1987). Our main purpose was to establish the particulate organic and inorganic transport of the river and its seasonal changes. Particulate material was sampled in surface and deep waters. Water conductivity ranges between 0.9 and 53 mS, and anoxia is common in summer situations. Particulate C ranges between 1 and 3 mg l−1 with higher values in summer; particulate N is very similar along the year with values between 0.1 and 0.5 mg l−1.Effects of regulation seem to be important in supplying very high nutrient content to algae and producing a high biomass and production in the lower part of the river, especially in summer. Diatoms and Chlorophyta are the most abundant groups. Phosphorus is higher than 5 μmol l−1, with lower values in summer. Most of particulate material is very fine (between 0.45 and 50 μm). The high biomass also explains the presence of abundant filter‐feeders, such as Hydropsyche and Ephoron virgo. In some parts, where light reaches the bottom, stones and boulders are covered by Cladophora. In this case, grazers such as the gastropods Melanopsis and Theodoxus are abundant.

Frontier Municipal Baths and Social Interaction in Thirteenth-Century Spain

THE TWELFTH AND THIRTEENTH CENTURIES were pivotal in the history of the Iberian Peninsula. The Reconquest created several large Christian principalities in the territory recovered from Islam, imposing a large number of northern Spaniards upon the south and fundamentally shaping the outlook of peninsular natives from that day to this.' As the Christian states drove to the south in an uneven series of thrusts, the Reconquest drained off the northern population, a drain which was never entirely replaced by extrapeninsular colonists and crusaders. During the struggle for the Guadiana and lower Ebro valleys in the mid-twelfth century, the north's population shortage made it difficult to find sufficient colonists for the conquered regions. The rulers of Leon, Castile, Aragon, and Catalonia were compelled to attract migrants by granting liberal municipal charters-fueros-that enlarged personal freedoms and immunities. The conquered towns of the south drew their Christian populations from an adventurous, mobile segment of the northern population willing to relocate on the edge of European civilization. In the southern municipalities aggressive Christian conquerors came into daily contact with an older, more urbane, and recently defeated native populace. The farther south the northern Christians penetrated, the older and deeper were the Arab and Berber civilizations they encountered. The Iberian municipalities that were the scene of this Muslim-Christian confrontation have received some attention from scholars over the last several decades, although a fresh examination in depth is still badly needed.2 The exploration of munici-

Rock Paintings of the Lower Ebro

A VERY interesting article on this subject by MM. l'Abbé Breuil and Juan Cabré appeared in the January-February number of l'Anthropologie. The first part of the paper deals with the painted rocks on the Calapatà at Cretas (Teruel) first observed by M. Cabré in 1903, although it was not until 1906 that he communicated his discovery, having then realised its significance in relation to Quaternary art. The pictures, which are painted under a shallow shelter, represent animals in various attitudes, and show considerable vigour of execution. Close by, flint flakes are to be found which exhibit no Neolithic characters, but rather Magdalenian. The paintings comprise three deer, a bull, and a small subject difficult to determine. All are done in dark red, and are outlined by a very, lightly engraved line; certain details, such as eyes and nostrils, are added in the same way, as they would not otherwise appear in a monochrome without shading. The first deer, measuring 30 cm. by 25 cm., is represented in a graceful attitude in the act of rising to its feet; the second (33 cm. by 27 cm.) is walking rapidly towards the first, the movement being admirably depicted. It is interesting to note that in all the stags drawn in profile the antlers are conventional, as if seen partly from the front, partly from the side. This curious disposition of the branching is met with, not only at Cretas, but also at Cogul (Lerida), and in France in the reindeer drawings of the Portel grotto. This points to a closer connection in late Quaternary times of the tribes of Aragon and Catalonia with those of the Ariege than with any others.