Signal crayfish are an internationally widespread invasive species that can have important detrimental ecological impacts. This thesis aims to determine whether signal crayfish have the potential to also impact the physical environment in rivers. A series of experiments were undertaken in purpose-built still-water aquaria using a laser scanner to obtain Digital Elevation Models (DEMs) of narrowly-graded gravel surfaces before and after exposure to crayfish. The difference between DEMs was used to quantify volumetric changes in surface topography due to crayfish activity. Two distinct types of topographic change were identified. The first was the construction of pits and mounds which resulted in an increase in surface roughness and grain exposure. The second was the rearrangement of surface material caused by crayfish brushing past grains when walking and foraging, reorientating grains and altering friction angles. A series of 80 flume runs were undertaken to quantify alterations made by crayfish to water-worked, as well as loose, gravel substrates at low velocity flows. Crayfish significantly altered the structure of water-worked substrates, reversing the imbrication of surface grains to a more random arrangement. Surfaces were entrained at a relatively high velocity flow subsequent to crayfish activity in order to directly link topographic and structural alterations to substrate stability. Nearly twice as many grains were mobilised from surfaces which had been disturbed by crayfish in comparison to control surfaces that were not exposed to crayfish. A field investigation aimed to determine the potential significance of the geomorphic impact of crayfish in rivers. Signal crayfish were tracked through a 20 m reach of a small, lowland alluvial river for 150 days using a Passive Integrated Transponder (PIT) system. Crayfish were active throughout the channel, although their activity became limited as water temperature dropped and flow stage increased. Substrate was not an important determinant of crayfish activity at this scale. Instead, crayfish tended to be found along the inner bank of a meander bend where there was a substantial cover of macrophytes. Consequently, signal crayfish were active for extended periods on substrates of a similar size to those that they could disturb in flume experiments. These results suggest that signal crayfish could have important geomorphic effects in rivers, disturbing bed structures and increasing the mobility of coarse material. This may have important implications for both the management of some rivers and benthic organisms that reside on the river bed.

No description available.

Upland rivers control the large-scale topographic form of mountain belts, allow coupling of climate and tectonics at the earth’s surface and are responsible for large scale redistribution of sediment from source areas to sinks. However, the details of how these rivers behave when perturbed by changes to their boundary conditions are not well understood. I have used a combination of fieldwork, remotely sensed data, mathematical analysis and computer modelling to investigate the response of channels to well constrained changes in the forcings upon them, focussing in particular on the effects of glacial remoulding of the catchments draining the south flank of the Ladakh batholith, northwest Indian Himalaya. The last glacial maximum for these catchments is atypically old (~100 ka), and this allows investigation of the response to glaciation on a timescale not usually available. The geomorphology of the catchments is divided into three distinct domains on the basis of the behaviour of the trunk stream – an upper domain where the channel neither aggrades above or incises into the valley form previously carved by glacial abrasion, a middle domain where the channel incises a gorge down into glacial sediments which mantle the valley floor, and a lower domain where the channel aggrades above this postglacial sediment surface. This landscape provides a framework in which to analyze the processes and timescales of fluvial response to glacial modification. The dimensions of the gorge and the known dates of glacial retreat record a time averaged peak river incision rate of approximately 0.5 mm/y; the timescale for the river long profile to recover to a smooth, concave up form must exceed 1 Ma. These values are comparable with those from similarly sized catchments that have been transiently perturbed by changing tectonics, but have never been quoted for a glacially forced basin-scale response. I have also demonstrated that lowering of the upper reaches of the Ladakh channel long profiles by glacial processes can systematically and nonlinearly perturb the slope-area (concavity) scaling of the channel downstream of the resulting profile convexities, or knickzones. The concavity values are elevated significantly above the expected equilibrium values of 0.3-0.6, with the magnitude controlled by the relative position of the knickzone within the catchment, and thus also by the degree of glacial modification of the fluvial system. This work also documents the existence of very similar trends in measured concavities downstream of long profile convexities in other transiently responding river systems in different tectonoclimatic settings, including those responding to changes in relative channel uplift. This previously unrecognised unity of response across a wide variety of different environments argues that such a trend is an intrinsic property of river response to perturbation. Importantly, it is consistent with the scaling expected from variation in incision efficiency driven by evolving sediment flux downstream of knickzones. The pervasive nature of this altered scaling, and its implications for fluvial erosion laws in perturbed settings, have significant consequences for efforts to interpret past changes in forcings acting on river systems from modern topography. I follow this by examining in detail the channel hydraulics of the Ladakh streams as they incise in response to the glacial perturbation. I present a new framework under which the style of erosion of a natural channel can be characterized as either detachment- or transport-limited based upon comparison of the downstream distribution of shear stress with the resulting magnitude of incision. This framework also allows assessment of the importance of sediment flux driven effects in studied channels. This approach is then used to demonstrate that fluvial erosion and deposition in the Ladakh catchments is best modelled as a sediment flux dependent, thresholded, detachment-limited system. The exceptional quality of the incision record in this landscape enables an unprecedented calibration of the sediment flux function within this incision law for three different trunk streams. The resulting curves are not compatible with the theoretically-derived parabolic form of this relation, instead showing nonzero erosion rates at zero sediment flux, a rapid rise and peak at relative sediment fluxes of less than 0.5 and a quasi exponential decrease in erosional efficiency beyond this. The position of the erosional efficiency peak in relative sediment flux space and the magnitude of the curve are shown to be both variable between the catchments explored and also correlated with absolute sediment flux in the streams.

This thesis uses geological field data and numerical ice sheet modelling to study the Younger Dryas ice cap in Scotland. The Younger Dryas stadial is important because it represents the most recent period of high-magnitude global climate change, and was marked by the expansion of ice sheets in North America and Scandinavia, and the regrowth of glaciers in the British Isles. An integrated methodology linking field results and modelling is developed and applied here, specifically focussing on the deposits, landforms, and palaeoglaciology of Younger Dryas glaciers in western Scotland. This combined approach enables data of different scales to be compared, and connected, from local sedimentological investigations and empirically derived reconstructions, to regional ice-sheet simulations from a high-resolution numerical model. Previous geological mapping in western Scotland resulted in contradictory views of the thickness and extent of ice during the Younger Dryas, consequently leading to uncertainty about the dynamics of the former ice cap. By using a ‘landsystem’ method to characterise the terrain, it is argued here that geological evidence in the study area implies a relatively thick central ice cap that fed steep outlet glaciers around its margins. These glaciers oscillated throughout the stadial, and during deglaciation produced suites of moraines that marked successive positions of glacier retreat. Widespread preservation of superimposed landforms, and of sediment sequences pre-dating the Younger Dryas, suggest that, despite being active, the Younger Dryas ice cap was not particularly erosive in its central area and only subtly modified its bed. These geological interpretations are supported by high-resolution numerical modelling of the ice cap, which reveals clear spatial variability in the velocity structure, thermal regime, and flow mechanism of the ice cap; patterns that led to local contrasts in basal processes and diversity in the geological imprint. These model experiments also highlight the non-linear relationship between climate forcing and glacier response, identifying evidence of ice sheet hysteresis and climatically decoupled glacier oscillations – concepts as relevant to geological investigations of former ice masses as they are to the prediction of glacier response under future climate changes.

This thesis aims to better understand the relationships between basal water pressure, friction, and sliding mechanisms at ice sheet scales. In particular, it develops a new subglacial hydrology model (Hydro) to explicitly predict water pressures in response to basal water production and water injection from the surface. Recent research suggests that the Greenland ice sheet (gis) is losing a substantial volume of ice through dynamic thinning. This process must be modelled to accurately assess the contribution of the gis to sea-level rise in future warming scenarios. A key control on dynamic thinning is the presence of water at the ice-bed interface; Zwally et al. (2002) highlight the importance of supraglacial lakes' impact on basal ice dynamics, a process now con rmed by Das et al. (2008) and Shepherd et al. (2009). Many studies focus on the effects of surface meltwater reaching the bed of the gis but the underlying processes are often ignored. Geothermal, strain, and frictional melting, which evolves with basal hydrology, provide the background basal pressure profile that surface meltwater perturbates. Without understanding how these heat terms affect the background profile it is difficult to define basal boundary conditions in models and therefore difficult to model the dynamic response of the gis to surface melting. Hydro tracks subglacial water pressures and the evolution of efficient drainage networks. Coupled with the existing 3D thermomechanical ice sheet model Glimmer, model outputs include effective pressure N and the efficient hydraulic area. Defining frictional heat flux and basal traction as functions of N allow the modelling of seasonal dynamic response to randomly draining supraglacial lakes. Key results are that frictional heat flux, as a function of N, caps potential runaway feedback mechanisms and that water converges in topographic troughs under Greenland's outlet glaciers. This leads to a background profile with low N under outlet glaciers. Therefore, outlet glaciers show a muted dynamic speedup to the seasonal surface signal reaching the bed. Land-terminating ice does not tend to have subglacial troughs and so has higher background N and consequently a larger seasonal response. This, coupled with effects of ice rheology, can explain the hitherto puzzling lack of observed seasonal velocity change on Jakobshavn Isbræ and other outlet glaciers.

1. Realigning rivers is becoming common as a solution to conflicting needs of land development and ecosystem preservation. Although an increasing number of projects are monitored, exactly how these channels develop as functional stream ecosystems is still poorly understood. Mining in the upper catchment of the River Nith (Scotland) required the realignment of 3km (approx.) of river. The engineered channel was designed around sound geomorphological principles of sediment transport and supply with a sinuous planform and pool-riffle sequences along the installed gravel-bed. 2. A comprehensive survey covering biotic and abiotic development was devised and implemented to test models and hypotheses relating to the development riverine habitats over the first three years. 2. Physical habitat development at the reach scale was investigated using fixed-point photography and differential GPS surveys of the thalweg and of cross-sectional form every 100m. This revealed the development of a relatively diverse streambed habitat in response to both the channel slope and planform. However, other than at meander bends where asymmetry developed over several years, little change was observed to the form of the engineered riverbanks. 3. Kick-net surveys of benthic invertebrate communities at 10 sites showed a negative relationship between specific measures of diversity and downstream distance during the early stages of development. (e.g. Richness with chainage at the 6 month stage) but the relationship degrades rapidly and is likely in part to appear as a result of low population densities. 4. Survey of transects through the riparian zone perpendicular to the river indicated that colonisation by vegetation is also related to distance along the realignment but physical habitat and geographical factors play a more dominant role over development (Canonical correspondence analysis of vegetation data in 2007) 5. Many of the indices of diversity for both biotic and abiotic elements of the ecosystem proved ineffective at detecting development at the reach scale. This may be because significant changes occur at a smaller scale than was detected by the surveys. It is likely that greater resolution is required to detect more ecologically meaningful relationships and patterns. 6. Overall study shows constructed realignments can rapidly develop a diverse streambed community within 24 months. Riparian communities are slower to develop because of the slow development of riverbank habitat diversity. Other ecosystem properties such as resilience and connectivity may take much longer.

The evolution of the lower course and estuary of the river Ribble (Lancashire, U.K.) during the Holocene is the object of study, along with the history of sediment fluxes in them and their influence on past human settlements. Investigation of the valley floor geomorphology and terrace fill stratigraphy and sedimentology, as well as palaeoecological analysis and a number of 14C essays, allowed the reconstruction of Late Pleistocene and Holocene alluvial history and chronology of a reach at the transition point between fluvial and estuarine influences; the archaeological evidence is evaluated in this context. Alluviation and incision cycles led to the formation of four river terraces. The oldest terrace, rich in coarse-grained materials, seems to be of Pleistocene age. 14C dating on the second terrace would point to an Earliest Holocene or Younger Dryas age; the fill, however, comprises abundant fine-grained overbank sediments. Large parts of the unit were reworked during a phase of lateral channel activity that occurred prior to ca. 8900 cal BP; between then and ca. 6900 cal BP the river underwent meander cut-offs, after which limited lateral activity occurred. New alluviation occurred around 4700 cal BP, possibly related to the aggradation of the third terrace, though its fill is only certainly known, from archaeological evidence, to be of pre-Roman age. Channel size increase occurred by the time the terrace was deposited. The fill features abundant clayey sediments; it was incised at or after the end of the Roman period. The last terrace was deposited in the late first millennium AD mainly as overbank silts, and has since been incised again. Fluvial response appears mainly related to climate changes, river activity corresponding to shifts to wetter, cooler climate. Human action likely enhanced fluvial response in the historical period, leading to post-Roman incision and deposition. There seems to be a good connection between sediment production in the catchment and deposition downstream. Local factors also show a major importance in determining river response. Early Holocene fluvial history finds no match in other Northern English rivers; a different response to the same climate changes is apparent, possibly related to differences in sediment supply conditions. No clear evidence is found supporting an influence of sea-level change on river processes. On the other hand, it appears plausible river sediment input has a driving influence in enhancing or causing minor regressions recorded on the estuary. The conditions existing in Roman times could have allowed access from the sea to the Roman sites at the upper end of the Ribble estuary and by its North shore; a relative sea-level minimum could have caused a shift of focus in naval traffic from the former to the latter site.

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Σκοπός της παρούσας μεταπτυχιακής διατριβής ειδίκευσης είναι η μελέτη της υδρογεωλογικής και υδροχημικής κατάστασης του νοτιοδυτικού τμήματος του συστήματος των Ακαρνανικών Ορέων. Η περιοχή μελέτης βρίσκεται στην Δυτική Αιτωλοακαρνανία. Ανήκει στην Ιόνια ζώνη, και καλύπτεται κατά κύριο λόγο από την μετα-Τριαδική ανθρακική ακολουθία, η οποία αποτελείται από τους Ασβεστόλιθους Παντοκράτορα, Ανώτερου Λιάσιου, Βίγλας, Σενωνίου και Παλαιόκαινου. Οι μεταλπικοί σχηματισμοί αποτελούνται από αλλουβιακές αποθέσεις, και πλευρικά ασβεστολιθικά κορήματα. Το ανάγλυφο της περιοχής είναι έντονο, με μεγάλα υψόμετρα ειδικά στο δυτικό τμήμα της. Η έντονη τεκτονική καταπόνηση της περιοχής παίζει καθοριστικό ρόλο στην εμφάνιση των πηγών καθώς και στη διαμόρφωση του υδροχημικού χαρακτήρα αυτών. Στην περιοχή αναπτύσσονται καρστικοί υδροφόροι στους ασβεστόλιθους Παντοκράτορα αλλά και ελεύθερος υδροφόρος στις αλλουβιακές αποθέσεις της κοιλάδας του Αστακού. Οι δυτικοί ασβεστολιθικοί όγκοι αποστραγγίζονται από σειρά πηγών κατά μήκος της επαφής των ασβεστόλιθων με το φλύσχη, ενώ εμφανίζονται και αρκετές υποθαλάσσιες πηγές. Στα πλαίσια της παρούσας εργασίας έγιναν δύο εκτεταμένες δειγματοληψίες κατά την ξηρή και υγρή περίοδο, καθώς και συλλογή δειγμάτων νερού και μετρήσεων παροχής σε επιλεγμένες πηγές σε μηναία βάση. Προσδιορίστηκαν οι κύριοι υδροχημικοί τύποι των νερών, οι οποίοι είναι Ca-HCO3 για τις καρστικές πηγές του δυτικού τμήματος, Ca-Mg-HCO3 και Ca-HCO3 για το κεντρικό τμήμα της περιοχής μελέτης. Παρατηρήθηκε επίσης υφαλμύρινση πηγής, η οποία εμφανίζεται στην επαφή ασβεστολίθων Ηωκαίνου με τις αλλουβιακές αποθέσεις και αποστραγγίζει το ανατολικό τμήμα της περιοχής, καθώς και σε υδροσημεία κατά μήκος αυτής της επαφής σε απόσταση έως 1,8 km από την θάλασσα. Ο υδροχημικός χαρακτήρας των νερών στο ανατολικό τμήμα της περιοχής μελέτης επηρεάζεται από τη διάλυση των Τριαδικών ανθρακικών λατυποπαγών, της γειτονικής περιοχής. Τέλος από τα υδρογράμματα των πηγών και τους συντελεστές στείρευσης που υπολογίστηκαν προέκυψε ότι η ροή του νερού γίνεται μέσω καρστικών αγωγών. / Τhe present master thesis deals with the hydrogeological and hydrochemical conditions of the SW part of the Akarnanika Mountains system in West Greece. The study area is located at West Aitoloakarnania. It’s a part of the Ionian Geotectonic Zone and is covered mainly by post-Triassic Carbonate series, which consists of “Pantokratoras” series, Upper Liasian limestones, “Vigla” series, and Palaiocene-Eocene Limestones. The post-Alpine formations consist of alluvial deposits and talus cones. The relief of the area is intense, reaching high altitudes especially in the western part of the area. The tectonic setting of the area plays an important role in the appearance of springs. Karstic aquifers are developed in the area, mainly in the “Pantokratoras” limestones. An unconfined aquifer is developed in the alluvial deposits which form the Astakos valley. The western limestone masses are drained by a series of springs, along the contact of limestone with flysch. Several submarine springs also occur. Within the frame of the thesis, two major sampling campaigns were conducted in the area, during the wet and dry period, accompanied with sampling and discharge measurements in selected springs on a monthly basis. The main hydrochemical types were defined, which are Ca-HCO3 for the karst springs of the western part and Ca-Mg-HCO3 and Ca-HCO3 for the central part. In the study area, seawater intrusion phenomena was observed in a coastal spring, draining the eastern part, at the contact of Eocene limestones with alluvial deposits, as well as on boreholes along this contact to a distance up to 1,8 km from the sea. The hydrochemical type of waters at the eastern part of the study area is defined by the dissolution of Triassic Carbonate Breccias that lie east of the study area. Finally spring hydrographs and the recession curves have shown that groundwater flows through karst conduits.

Στα πλαίσια της παρούσας διπλωματικής μεταπτυχιακής εργασίας γίνεται υδρογεωλογική, υδροχημική και περιβαλλοντική έρευνα του καρστικού συστήματος των Τριαδικών ανθρακικών λατυποπαγών που εκφορτίζεται στο μέτωπο των πηγών ‘’Λάμπρας’’ ή Αγ. Δημητρίου στην ευρύτερη περιοχή του νότιου Ξηρόμερου, ΝΔ Αιτωλακαρνανίας. Η περιοχή ανήκει στην Ιόνια ζώνη με υπόβαθρο τους Τριαδικούς εβαπορίτες, τα φαινόμενα διαπειρισμού των οποίων έχουν συντελέσει, σε συνδυασμό με το τεκτονικό περιβάλλον της ζώνης, στον σχηματισμό και την ανάπτυξη των Τριαδικών ανθρακικών λατυποπαγών (ΤΑΛ). Επίσης στην περιοχή απαντούν με περιορισμένη εξάπλωση οι σχηματισμοί της μετά-Τριαδικής Ανθρακικής ακολουθίας, που αποτελείται από τους Ιουρασικούς Ασβεστόλιθους ‘’Παντοκράτορα’’, τους ασβεστόλιθους Λιάσιου και τους Κρητιδικούς Ασβεστόλιθους του σχηματισμού της ‘’Βίγλας’’. Απαντούν επίσης μεταλπικοί σχηματισμοί, όπως τεταρτογενείς αποθέσεις με εναλλαγές μαργών και terra rossa, μάργες και αλλουβιακές αποθέσεις. Ο υπό μελέτη καρστικός υδροφόρος αναπτύσσεται στα ΤΑΛ και οριοθετείται προς βορρά από την διαπιστωμένη με γεωφυσικές μεθόδους αναθόλωση των εβαποριτών στην περιοχή Φυτείες και προς τη δύση από την εφίππευση των ΤΑΛ στους Ιουρασσικούς ασβεστόλιθους ‘’Παντοκράτορα’’ των Ακαρνανικών Ορέων. Η περιοχή χαρακτηρίζεται από την ανυπαρξία υδρογραφικού δικτύου Η εκφόρτιση του συστήματος γίνεται από ένα πλήθος (>20) πηγών, στην επαφή των ΤΑΛ με τις τεταρτογενείς αποθέσεις του κάμπου του Λεσινίου. Το μέτωπο των πηγών της ‘’Λάμπρας’’ έχει μήκος ~3km και μέση ετήσια παροχή ~270*106m3/yr. Απαντά επίσης ένα μικρότερο, δυτικό μέτωπο εκφόρτισης με διαφοροποιήσεις στο χημισμό του νερού και μεγαλύτερη συγκέντρωση αλάτων. Οι πηγές έχουν χημισμό Ca-SO4-HCO3, ανάλογο των βασικών χημικών τύπων που προσδιορίστηκαν στα υπόγεια ύδατα ύστερα από την υδροχημική έρευνα. Τα νερά του συστήματος διακρίθηκαν σε δυο κύριες κατηγορίες και δυο δευτερεύουσες: Τους τύπους Ca-SO4-HCO3, Ca- HCO3-SO4 που αποτελούν τον κυρίαρχο τύπο των υδάτων της περιοχής και τους τύπους Ca-SO4 και Ca-Na-SO4-HCO3 που αφορούν τμήματα της περιοχής. Η αυξημένη συγκέντρωση των θειικών ιόντων οφείλεται στην αλληλεπίδραση του νερού με τους εβαπορίτες του υποβάθρου. Ο φυσικός εμπλουτισμός του υπόγειου υδροφόρου υπολογίσθηκε μέσα από την εφαρμογή του μοντέλου APLIS στο ~45% του νερού της βροχής. Η μεγάλη παροχή των πηγών, συγκριτικά και με την μέση ετήσια βροχόπτωση ~850mm/yr οφείλεται στην τροφοδοσία από την πλευρική διήθηση του Αχελώου στο καρστικό σύστημα, κάτι που επιβεβαιώθηκε και από την υδρογεωλογική και υδροχημική έρευνα με ποσοστά συμμετοχής που φτάνουν και το 90% στις πηγές του ανατολικού ορίου του μετώπου και με μέσο όρο συμμετοχής >50%. Μικρότερης σημασίας τροφοδοσία φαίνεται να λαμβάνει χώρα από την λίμνη του Οζερού, στο ΒA όριο της περιοχής μελέτης. Η υδροχημική έρευνα έδειξε επίσης ότι η τροφοδοσία του Αχελώου αποτελεί βασικό παράγοντα της μεταβολής της ποιότητας του υπόγειου νερού και του χημισμού των πηγών. / The purpose of the present thesis is the hydrogeological, hydrochemical and environmental investigation of the karstic system of the Triassic Carbonate Breccia (TCB) which discharges through the spring front of ‘’Lambra’’ and lies in southern Ksiromero, SW Aitoloakarnania. The study area is part of the Ionian Zone and its geological background consists of the Triassic Evaporites. The TCB where formed under the combination of the tectonic and orogenetic setting of the External Hellenides and the diapir phenomena of the Triassic Evaporites. The after-Triassic Carbonate series is also present in the study area, with limited expansion, which consists of the Jurassic Limestones known as ‘’Pantokratoras Limestones’’, the Lias Limestones, the Cretaceus Limestones of the ‘’Vigla’’ formation and the Eocene Limestones. Recent formations are also present: Quartenary sediments with marl and terra rossa variations, marls and alluvial sediments. The karstic aquifer develops through the TCB and its margins are defined by the diapir phenomena in the area of Fities in the North, the Mahalas thrust in the east and the overthrust of the TCB onto the Jurassic ‘Pantokratoras’’ Limestones in the West. The discharge of the karstic system of the TCB consists of numerous springs (>20) in the contact of the TCB with the quartenary deposits of the Lesini Fields. The spring front of Lambra is 3km long with mean annual discharge ~270*106m3/yr. A secondary discharge front is present in the West of the main front with alterations in the water chemism and larger ion concentrations. The hydrochemical type of the springs water is Ca-SO4-HCO3. The hydrochemical investigation provided two major and two minor hydrochemical types for the groundwater: The main types Ca-SO4-HCO3 and Ca- HCO3-SO4 and the secondary types Ca-SO4 and Ca-Na-SO4-HCO3. The elevated concentration of the sulfur anions is due to the interaction of the water with the Triassic Evaporites of the background. The recharge rate of the karstic aquifer was estimated with the application of the APLIS model as the 45% (approx.) of the annual precipitation. The large discharge measurements of the spring front, also compared with the annual precipitation of the study area (~850mm/yr) is due to the side infiltration of the Acheloos River into the karstic system in the Paleomanina area, which was also confirmed after hydrogeological investigations. The participation of the Acheloos water was calculated up to 90% of the spring discharge in the eastern springs of the Lambra front and with a mean participation of over 50% (approx.). Minor participation seems to take place through side infiltrations of the karstic lake Ozeros’ water, in the NE margin of the study area. Hydrochemical investigations also presented that Acheloos’ participation in the aquifer is a main factor of the hydrochemical and quality variations of the groundwater and of the chemism of the springs water.