flow to horizontal drains in isotropic unconfined aquifers the laplace transform solution for the problem of flow to horizontal drains in an anisotropic unconfined aquifer is derived the solution for the constant flux horizontal well by zhan and zlotnik zhan h zlotnik v a 2002 groundwater flow to a horizontal and slanted well in an unconfined aquifer water resour res 38 7 13 1 13 11 is modified to obtain the solution for a constant head horizontal drain the laplace transform solution is converted to the real time domain and type curves for the drawdown around and the discharge to a horizontal drain are computed the solution is verified by a numerical simulation the type curves and derivative type curves of the drains are compared with type curves for horizontal wells the sensitivity of type curves on piezometer location specific storage horizontal drain elevation aquifer delay index and drain length is tested these type curves can be used for interpretation of drainage data

are the seismological and geological observations of the al hoceima morocco rif 2004 earthquake m 6 3 contradictory abstract seismic hazard is associated with recent and present fault activity in mountain ranges in the betic rif alpine mountain chain tectonic activity started in the cretaceous and topographic uplift continues since tortonian times as a consequence of the nw se oblique convergence between africa and eurasia the deformation is active and produces seismicity that sometimes has catastrophic consequences the al hoceima earthquake february 24 2004 considered one of the largest earthquakes ever recorded instrumentally in the westernmost mediterranean m 6 3 caused great damage in the region seismological studies agree that the main shock was situated on land at the limit between the external and internal zones of the rif at a depth of 10 14 km the focal mechanism points to a strike slip solution with a nw se oriented p axis quite similar to those of the significant 1994 earthquake swarm located to the north the epicenter aftershocks distribution would signal the presence of a n s oriented sinistral fault activated by the nw se regional compression associated to plate boundary convergence in this setting the seismogenic fault ruptures related to these seismic events are expected to have reached the earth s surface however detailed field work carried out 1 month after the earthquake does not evidence any n s strike slip coseismic fault in the epicentral area the main observed effects were landslides damages to constructions and locally open cracks indicating an unexpected nw se extension scarce n s faults are normal the main ones being located several kilometers away from the epicentral area to explain this apparent contradiction between geological and seismological observations we propose a decoupled tectonic model with crustal detachments that separate a deep brittle crust from an upper crust undergoing uplift and the development of large folds and normal faults this geological setting common to internal zones of cordilleras may need to be taken into account in future paleoseismicity studies and in the assessment of seismic hazard

hydrological flowpaths and nitrate removal rates within a riparian floodplain along a fourth order stream in brittany france three main reservoirs were identified that contribute to the shallow subsurface flow regime of a valley drained by a fourth order stream in brittany western france i an upland flow that supplied a wetland area mainly during the high water period it has high n no3 and average cl concentrations ii a deep confined aquifer characterized by low nitrate and low chloride concentrations that supplied the floodplain via flow upwelling iii an unconfined aquifer under the riparian zone with high cl and low n no3 concentrations where biological processes removed groundwater nitrate this aquifer collected the upland flow and supplied a relict channel that controlled drainage from the whole riparian zone patterns of n no3 and cl concentrations along riparian transects together with calculated high nitrate removal indicate that removal occurred mainly at the hillslope riparian zone interface i e first few metres of wetland whereas dilution occurred in lower parts of the transects especially during low water periods and at the beginning of recharge periods stream flow was modelled as a mixture of water from the three reservoirs an estimation of these contributions revealed that the deep aquifer contribution to stream flow averaged 37 throughout the study period while the contribution of the unconfined reservoir below the riparian zone and hillslope flow was more variable from ca 6 to 85 relative to rainfall events and the level of the riparian water table at the entire riparian zone scale no3 removal probably from denitrification appeared most effective in winter despite higher estimated upland no3 fluxes entering the riparian zone during this period copyright 2003 john wiley sons ltd

a two dimensional transient analytical solution for a ponded ditch drainage system under the influence of source sink abstract an analytical solution is developed for predicting two dimensional transient seepage into ditch drainage network receiving water from a non uniform steady ponding field from the surface of the soil under the influence of source sink in the flow domain the flow domain is assumed to be saturated homogeneous and anisotropic in nature and have finite extends in horizontal and vertical directions the drains are assumed to be standing vertical and penetrating up to impervious layer the water levels in the drains are unequal and invariant with time the flow field is also assumed to be under the continuous influence of time space dependent arbitrary source sink term the correctness of the proposed model is checked by developing a numerical code and also with the existing analytical solution for the simplified case the study highlights the significance of source sink influence in the subsurface flow with the imposition of the source and sink term in the flow domain the pathline and travel time of water particles started deviating from their original position and above that the side and top discharge to the drains were also observed to have a strong influence of the source sink terms the travel time and pathline of water particles are also observed to have a dependency on the height of water in the ditches and on the location of source sink activation area

groundwater flow to a horizontal or slanted well in an unconfined aquifer 1 new semianalytical solutions for evaluation of the drawdown near horizontal and slanted wells with finite length screens in unconfined aquifers are presented these fully three dimensional solutions consider instantaneous drainage or delayed yield and aquifer anisotropy as a basis solution for the drawdown created by a point source in a uniform anisotropic unconfined aquifer is derived in laplace domain using superposition the point source solution is extended to the cases of the horizontal and slanted wells the previous solutions for vertical wells can be described as a special case of the new solutions numerical laplace inversion allows effective evaluation of the drawdown in real time examples illustrate the effects of well geometry and the aquifer parameters on drawdown results can be used to generate type curves from observations in piezometers and partially or fully penetrating observation wells the proposed solutions and software are useful for the parameter identification design of remediation systems drainage and mine dewatering

the al hoceima morocco earthquake of 24 february 2004 analysis and interpretation of data from envisat asar and spot5 validated by ground based observations abstract the magnitude mw 6 3 earthquake in al hoceima morocco of 24 february 2004 occurred in the active plate boundary accommodating the oblique convergence between africa and eurasia three different sets of estimates of its source parameters have already been published we try to resolve the discrepancies between them by using additional data including two remote sensing satellite systems envisat and spot5 using a model with a dislocation in an elastic half space we constrain the source parameters the hypothesis of two subevents on distinct faults as inferred from seismological inversions is confirmed here by adopting a cross fault mechanism the rupture began on a left lateral strike slip fault striking at n10 azimuth with 90 cm of horizontal slip and then transferred to a right lateral strike slip fault striking at n312 azimuth with 85 cm of horizontal slip the first fault is at 500 m depth from the free surface and the second fault is at 3 km depth this model is consistent with ground based observations including gps seismology and mapped surface fissures the pair of faults activated in 2004 appears to constitute part of a complex seismogenic structure striking nne ssw that separates the rif tectonic blocks

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

neodymium and lead isotope evidence for enriched early archaean crust in north america there has been considerable debate as to whether isotopically enriched continental crust was an important geochemical reservoir in earliest archaean times fundamental questions such as the volume of the early crust its composition and the effect of its formation and or recycling on mantle geochemistry have still to be answered the most direct clues to the nature of the earliest crust and mantle are obtained from the isotope systematics of old rocks1 5 here we report neodymium and lead isotope measurements and uranium lead zircon geochronology from archaean gneisses of the slave province northwest territories canada the gneisses contain zircons with cores older than 3 842 gyr one sample of tonalitic gneiss has a nd chondritic model age of 4 1 gyr and an end 3 7 gyr of 4 8 this is the oldest reported chondritic model age for a terrestrial sample and provides evidence for strongly enriched pre 3 8 gyr crust a reservoir complementary to the depleted mantle already in existence by 3 8 gyr before present2 6

a process based transfer function approach to model tile drain hydrographs tile drain response to rainfall events is determined by unsaturated vertical flow to the water table followed by horizontal saturated water movement in this study unsaturated vertical movement from the redistribution of water is modelled using a sharp front approximation and the saturated horizontal flow is modelled by an approximate solution to the boussinesq equation the unsaturated flow component models the fast response that is associated with the presence of preferential flow paths by convoluting the responses of the two components a transfer function is developed that predicts tile drain response to unit amounts of infiltrated water it is observed that the unsaturated flow component can be cast in a form that is linear in a power function of the infiltrated depth since the approach is process based model parameter definitions are easily identified with soil properties at the field scale furthermore it is demonstrated that the transfer function model parameters can be estimated from moment analysis using superposition the transient tile drain response to arbitrary amounts of infiltrated water can be constructed comparison with data measured from the water quality field station show that this approach provides a promising method for generating tile drain response to rainfall events copyright 2006 john wiley sons ltd

source analysis of the mw 6 3 2004 al hoceima earthquake morocco using regional apparent source time functions 1 we use small and moderate aftershocks of the 24 february 2004 al hoceima earthquake as empirical greens functions egfs to retrieve the rupture history of the main event the magnitude depth and geometry of faulting were estimated for the main shock and 20 small and moderate aftershocks mw between 3 9 and 5 2 computing moment tensor solutions for the main shock we obtain a moment magnitude of mw 6 3 and a nearly pure double couple source 4 compensated linear vector dipole with predominately strike slip faulting the preferred fault plane has a strike of n11 e a dip of 72 and a rake of 17 fourteen aftershocks having depths 4 km and faulting geometries 11 for the strike of the preferred plane similar to the ones found for the main event were used as egfs apparent source time functions astfs of the al hoceima event were retrieved at twelve regional stations using an iterative time domain deconvolution on the p waveforms at each station time functions are enhanced by stacking of the deconvolved waveforms for different egfs astfs show total durations of 5 to 6 s two consecutive subevents separated by about 3 s and only a weak effect of directivity we further investigate the source history by inverting the set of astfs for the distribution of fault slip and rupture propagation two different source models were selected for presentation one involving one single fault plane and the other involving two parallel fault planes the two fault model fits more accurately the observations and leads to a more plausible slip distribution we estimate rupture dimensions of about 10 10 km2 and 8 8 km2 and moment magnitudes of mw 6 2 and 6 0 for the first and second subevent respectively

the alboran sea western mediterranean revisited with a view from the moroccan margin this paper presents a new depth to acoustic basement map based on a grid of seismic profiles in the western alboran basin the basement is more than 10 km deep an examination of a seismic profile of this region suggests that late oligocene early miocene 5 km thick synrift formation has been accumulated in this basin this west alboran basin has been formed in an extensional setting but in a fore arc position south of the balearic islands then westwards transported behind a subduction zone

nd and sr isotope systematics of clastic metasediments from isua west greenland identification of pre 3 8 ga differentiated crustal components recent field work on the isua metasediments has established that there are two lithological sequences a and b which are divided into a number of distinct formations each clastic metasedimentary unit has a relatively unique trace element signature the depleted mantle sm nd model ages of samples from all major units range from 3 59 to 3 98 ga whereas rb sr model ages cover a very wide range 1 9 4 6 ga the samples from the sequence a felsic gneiss formation a6 yield a relatively good rb sr isochron age of t 3 71 0 07 ga the sequence b samples do not yield a rb sr isochron however some of the samples plot close to the a6 rb sr isochron and sequences a and b appear to have essentially the same deposition age the sm nd data for both sequences yield initial end values in the range 1 to 3 for a deposition age tstrat 3 64 ga if tstrat 3 81 ga the range is 0 4 this range appears to reflect real variability of initial end values corresponding to the time of deposition data trends in end versus 1 nd diagrams suggest at least three distinct components in each of sequences a and b model age calculations suggest that some of these components must be derived from continental crustal sources that predate the time of deposition of these sediments by as much as 0 4 b y other components appear to be derived from volcanic sources that are roughly coeval with sediment deposition the very high initial end values implied for early depleted mantle sources 2 to 4 suggest a very large pre 3 8 ga continental crust alternatively these high values could reflect an early terrestrial mantle with highly fractionated cumulate layers that formed in a 4 5 ga magma ocean

analytical solutions for two dimensional groundwater flow with subsurface drainage tiles summary the tile drainage problem in an unconfined aquifer was investigated a mathematical model was established that describes two dimensional groundwater flow in an unconfined aquifer near a river with a linearized boussinesq equation time dependent sources and a sloped tile analytical solutions for groundwater level and discharge were derived and used to compare hydrologic conditions in a system with and without tile natural drainage we found that the spatial and temporal variations of groundwater level and discharge were significantly altered by the presence of drainage tile in an aquifer with tile drainage the groundwater level was lower and total groundwater discharge to the river increased compared to an aquifer with no tile application of the solutions to a synthetic case demonstrates that the analytical solutions derived can be used to quantify effect of tiles on nitrate loads in the baseflow of a river and assess the effectiveness of various conservation practices

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

a semi analytical model for transient flow to a subsurface tile drain the goal of this paper is to develop and test a semi analytical model for event based transient flow to a subsurface tile drain a sharp front theory was used to describe redistribution of infiltrated water in the vadose zone new approximate analytical solutions in terms of fourier series were sought for the boussinesq equation describing subsurface saturated flow subject to time dependent recharge both one and two term solutions of the series approximation were compared with observed tile hydrograph data from the purdue water quality field station wqfs in west lafayette indiana in general the models were able to capture the peaks of the tile drain hydrographs as well as the times to peak and the times of initial response to rainfall events the models performed particularly well for rainfall events with single burst hyetographs and in the prediction of the first hydrograph peak from multiple burst hyetographs though subsequent peaks could not be captured as well a further comparison of results from the one term model with those from hydrus 2d suggested that the one term model is adequate for estimating transient flow to a tile drain the solution developed here holds promise for extension to larger watersheds where the hydrology is governed by tile drains

a new analytical method for groundwater recharge and discharge estimation summary a new analytical method was proposed for groundwater recharge and discharge estimation in an unconfined aquifer the method is based on an analytical solution to the boussinesq equation linearized in terms of h2 where h is the water table elevation with a time dependent source term the solution derived was validated with numerical simulation and was shown to be a better approximation than an existing solution to the boussinesq equation linearized in terms of h by calibrating against the observed water levels in a monitoring well during a period of 100 days we shown that the method proposed in this study can be used to estimate daily recharge r and evapotranspiration et as well as the lateral drainage it was shown that the total r was reasonably estimated with a water table fluctuation wtf method if the water table measurements away from a fixed head boundary were used but the total et was overestimated and the total net recharge was underestimated because of the lack of consideration of lateral drainage and aquifer storage in the wtf method

new gps constraints on active deformation along the africa iberia plate boundary abstract we use velocities from 65 continuous stations and 31 survey mode gps sites as well as kinematic modeling to investigate present day deformation along the africa iberia plate boundary zone in the western mediterranean region the gps velocity field shows southwestward motion of the central part of the rif mountains in northern morocco with respect to africa varying between 3 5 and 4 0 mm yr consistent with prior published results stations in the southwestern part of the betic mountains of southern spain move west southwest with respect to eurasia 2 3 mm yr the western component of betics motion is consistent with partial transfer of nubia eurasia plate motion into the southern betics the southward component of betics motion with respect to iberia is kinematically consistent with south to southwest motion of the rif mountains with respect to africa we use block modeling constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures our preferred plate boundary geometry includes one block between iberia and africa including the sw betics alboran sea and central rif this geometry provides a good fit to the observed motions suggesting a wide transpressive boundary in the westernmost mediterranean with deformation mainly accommodated by the gloria azores fault system to the west and the rif tell lineament to the east block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles i extension along the ne sw trending trans alboran shear zone ii dextral strike slip in the betics corresponding to a well defined e w seismic lineament and iii right lateral strike slip motion extending west to the azores and right lateral motion with compression extending east along the algerian tell we interpret differential motion in the rif alboran betic system to be driven both by surface processes related the africa eurasia oblique convergence and sub crustal dynamic processes associated with the long history of subduction of the neotethys ocean lithosphere the dextral slip identified in the betic mountains in southern spain may be related to the offshore fault that produced the great 1755 lisbon earthquake and as such may represent a significant seismic hazard for the west mediterranean region

microearthquake seismicity and fault plane solutions around the nekor strike slip fault morocco abstract three hundred and twenty eight earthquakes recorded in the course of 5 weeks in 1989 in the central rif of northern morocco provided no evidence for activity on the nekor fault the principal geological structure in the region itself most of the seismicity is located northwest of the nekor fault most of the 41 fault plane solutions show mainly strike slip motion left lateral on n s striking planes with p axes trending n145 this deformation is consistent with the n s trending normal faults caused by the e w quaternary extension and with the present relative nw se convergence between africa and europe the active deformation around the eastern rif is better represented by a distributed shear zone than by a strike slip fault

energy flow and geosphere interactions archaean to the present the foundation of the global resource base abstract direct observation of processes on modern earth have shown that the cooling processes lead to geochemical mixing influencing all the geospheres and the continental crust in the past two decades the importance of water cooling and hydrosphere interactions with the outer 10 km or so of the crust have explained a host of chemical and isotopic features today new attention is being focused on the role of the biomass in earth chemistry and the scale of the processes almost all of our most basic resources metals fossil fuels fertile soils involved the interactions of atmosphere hydrosphere biosphere with the outer shells of earth new needs in waste management technologies involve use of the same knowledge while there can be no doubt that the ancient earth was more energetic there is still no general agreement on the main styles of convection perhaps reflecting more chaotic tectonics but for sure the biosphere was alive and well

where has all the old crust gone geophysicists have come to believe that the earth was covered with a thick crust more than four billion years ago new measurements challenge that theory indicating the importance of crustal destruction in earth s early history

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

development of asymmetric basins along continental transform faults abstract many basins associated with wrench or transform faults are asymmetrical both longitudinally and laterally the sense of basin asymmetry changes along the strike of transform faults geophysical data from the dead sea rift and other transforms indicate that wrench induced asymmetric basins are bounded on only one side by a transform fault this implies that during the evolution of such basins maximum compression was parallel to the transform the direction of extension can change during the geologic evolution of a basin a possible explanation of this observation takes the strength of the fault into into consideration in the case of a weak fault in a strong crust the horizontal principal stresses would probably rotate to orientations parallel and perpendicular to the fault thus minimizing the shear stress on the main fault basins formed by regional extension such as in the east african rift system sometimes show similar features recent studies have shown that these basins often undergo oblique extension this suggests that the asymmetry in these basins may result from simultaneous strike slip motion and fault normal extension similar to the way asymmetry is produced in large transform basins periods of oblique extension can alternate with periods of orthogonal extension the asymmetry formed during periods of oblique extension is often preserved in the stratigraphic record

high resolution imagery of active faulting offshore al hoceima northern morocco abstract two recent destructive earthquakes in 1994 and 2004 near al hoceima highlight that the northern moroccan margin is one of the most seismically active regions of the western mediterranean area despite onshore geodetic seismological and tectonic field studies the onshore offshore location and extent of the main active faults remain poorly constrained offshore al hoceima high resolution seismic reflection and swath bathymetry have been recently acquired during the marlboro 2 cruise these data at shallow water depth close to the coast allow us to describe the location continuity and geometry of three active faults bounding the offshore nekor basin the well expressed normal left lateral onshore trougout fault can be followed offshore during several kilometers with a n171 e 3 trend westward the bousekkour aghbal normal left lateral onshore fault is expressed offshore with a n020 e 4 trending fault the n030 e 2 bokkoya fault corresponds to the western boundary of the plio quaternary offshore nekor basin in the al hoceima bay and seems to define an en echelon tectonic pattern with the bousekkour aghbal fault we propose that these three faults are part of the complex transtensional system between the nekor fault and the al idrissi fault zone our characterization of the offshore expression of active faulting in the al hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses as well as seismological geodetic and geodynamic data

field scale modeling of subsurface tile drained soils using an equivalent medium approach research conducted for the last 35 years has shown that subsurface drainage has a significant impact on hydrology and contaminant transport this can be observed at the field scale and also at the watershed scale impacts are always associated with modifying otherwise natural flow paths most computer model representations of drainage have been drawn at the field scale these models require relatively precise data that are usually unavailable when simulating hydrology and water quality in large watersheds we believe that in this case drainage representation should be simplified and yet closely match observations as a first step towards incorporating drainage systems into large scale hydrological models we propose an equivalent representation of drains buried in a soil profile by using a homogeneous anisotropic porous medium without drains this representation is based on a self consistent approach and on geometrical considerations simplification is such that calculating the equivalent hydraulic conductivity requires only information on the main length and spacing of the tile drains and not on their precise location this approach also provides a much simpler discretisation of the domain because of the absence of internal boundary conditions on the drainage pipes compared to other methods that have simplified drainage representation in existing watershed models it requires no parameter fitting two alternatives to the method are presented in the first one the soil profile equipped with the actual drain pipes is represented by an equivalent horizontally layered system with no pipes in the second the layered system has been replaced with an equivalent homogeneous profile the efficiency of these approaches was tested against a classical representation of tile drains using the swms 3d code which solves the richards equation for a typical drained plot configuration the equivalent medium approach appears to give satisfying results for global water outflow and mean water table elevation

la marge meridionale de la mer d alboran caracteres structuro sedimentaires et evolution recente abstract high resolution seismic reflection profiles 2000 km were collected across the southern continental margin and major structural trends of the alboran sea seismic units are dated on the basis of well known marine neogene onshore sections and offshore dredged samples a better assessment of margin structuration and neogene chronology is made a conformable succession of pliocene quaternary and older series provides evidence for the non evaporitic nature of the upper miocene similar to the facies from the onshore neogene boudinar and melilla basins it also suggests that alboran ridge is in part sedimentary rather than only volcanic this ridge appears as an en echelon anticlinal complex conformable upper miocene and lower pliocene quaternary strata are folded and faulted primarily important manifestation of the movements is dated as pliocene but the main vertical relative movements are of quaternary to recent age as emphasized by well developed divergent strata lying above submarine volcanism probably miocene in age often controls the morphology and structure of the eastern moroccan continental margin and adjacent south alboran basin the latter one is characterised by a thick sedimentary accumulation it is tectonically bounded except on the southwestern part seaward of the bokkoyas cliffs vertical movements occur during much of plio quaternary time prevailing during the quaternary the structure and related morphology of the study area are mainly the result of neotectonic events