Although blanket peat covers many major headwater areas in Britain, runoff production within these upland catchments is poorly understood. This thesis examines runoff production mechanisms within the blanket peat catchments of the Moor House National Nature Reserve, North Pennines, UK. Catchments ranging from 11.4 km^ down to the hillslope and plot-scale are examined. Runoff from the monitored catchments was flashy. Lag times are short and rainwater is efficiently transported via quickflow- generating mechanisms such that flood peaks are high and low flows poorly maintained. Hillslope and plot-scale runoff measurements show that the flashy catchment response is the result of the dominance of overland flow. Typically 80 % of runoff is produced as overland flow. This occurs both on bare and vegetated surfaces. Most of the remaining runoff is generated from the upper 10 cm of the peat, except where well-connected macropore and pipe networks transfer flow through the lower layers. Below 10 cm depth the blanket peat matrix fails to contribute any significant runoff Thus most groundwater-based models of peat hydrological process are not readily applicable to these catchments. Suggestions that infiltration-excess overland flow may be largely responsible for the flashy regime of these upland catchments are not substantiated by the blanket peat infiltration data presented in this thesis. Monitoring of hillslope runoff mechanisms combined with rainfall simulation (at realistic intensities of 3-12 mm hr(^-1)) and tension- infiltrometer experiments shows that saturation-excess mechanisms dominate the response. Infiltration is relatively rapid in the upper peat layers until they become saturated and overland flow begins. High water tables result in rapid saturation of the peat mass such that even at low rainfall intensity runoff production is just as efficient as during high intensity events. While macropores have largely been ignored in blanket peat, results presented suggest that up to 30 % of runoff may be generated through them. Occasionally these macropore networks develop through the deeper peat such that runoff bypasses the matrix and runs off at depth from small outlets and larger pipe networks. Seasonal variations in runoff- generating processes can be exacerbated by drought which causes structural changes to the near-surface of the peat. This was found to result in enhanced infiltration and macropore flow which may encourage pipe network development. Flow has been monitored simultaneously from several natural pipes in a 0.4 km(^2) headwater catchment of the Tees. This catchment provides one of the few examples of pipeflow monitoring outside the shallow peaty-podzols of mid-Wales. Natural pipes are found throughout the soil profile and can be at depths of up to three metres. Ground penetrating radar was useful in identifying deep subsurface piping and suggestions are made for improvements to the application. The pipe networks were found to be complex and results demonstrate that outlet location and size may bear little relation to the form and depth of the pipe a short distance upslope. Pipes generally contribute less than 10 % to catchment runoff but on the rising and falling hydrograph limbs can contribute over 30 % to streamflow. Pipeflow lag times are short suggesting that both the shallow and deep pipes may be well connected to the surface. Thus while matrix runoff contributions at depth within the peat may be low, macropore flow mechanisms can be significant.

Variations in drainage density have been observed in a range of environments as the perennial stream network expands into headwater reaches. This network expansion and contraction results in large changes in drainage density and as such, has implications for the connectivity of the catchment and the associated flux of water, sediments and solutes. One environment where these changes have been observed is peatlands. The accurate characterisation of catchment connectivity in peatlands is desirable for a number of reasons, not least to understand the controls on carbon flux. In addition, the accurate characterisation of these systems will help us to predict the impacts of a changing climate. It is hitherto been difficult to quantify changes in connectivity due to the logistical difficulties of monitoring this phenomenon. The use of Electrical Resistance (ER) technology has shown potential to detect the presence and absence of water. This method is built on here and a range of sensors are developed to monitor connectivity at high temporal and spatial resolutions, specifically flow in ephemeral portions of the channel network, pipeflow and overland flow. The study takes places in the Upper North Grain research catchment, a small peatland headwater catchment in the south Pennines, UK. The data collected on ephemeral streamflows highlight the importance of water table as a control on changes in network extent in the study catchment, as the presence or absence of flow at each site is strongly controlled by local water table. This allows the minimum and maximum drainage density within the catchment to be determined, as well how frequently these states occur. Pipe stormflow generation appears to be strongly linked to the production of saturation excess overland flow. The pipe network is very sensitive to small inputs of rainfall. In contrast, pipe baseflows seem to be controlled by water table level as pipes are fed by seepage from the peat mass. Pipe behaviour could not be related to any of the morphological characteristics presented here and is though to be dependent on the subsurface morphology of the pipe network. Overland flow production was monitored at a gully head and gully side location. At the gully head the incidence of overland flow increased with distance from the gully edge due to higher local water tables encouraging the production of saturation excess overland flow. At the gully side, extreme water table drawdown has caused the peat to become hydrophobic and the incidence of overland flow is high here, due to infiltration excess. This signifies a major advancement in our knowledge of runoff pathways in peatlands as the importance of infiltration excess overland flow has not been acknowledged until now. In general, ephemeral streamflows occur before the production of either overland flow or pipeflow as incident rainfall causes saturation of the gully floors. The temporal pattern of overland flow and pipeflow is similar, although pipeflow continues after overland flow ceases and is thought to be fed by shallow subsurface flow on the recession limb. Both overland flow and pipeflow precede discharge at the catchment outlet by several minutes. The interaction of these processes is examined under both ‘wet’ and ‘dry’ antecedent conditions. The data collected here provide an accurate characterisation of the dynamics of, and controls on, peatland connectivity under current climatic conditions, providing a reference point to which future observations can be compared.

Preferential flow paths are areas of substantially higher permeability than surrounding media. Macropores and soil pipes are a type of preferential flow path where conduit-like voids in the subsurface are typically greater than three millimeters in diameter. They are known to occur in agricultural and forest soils, often as a result of biological and physical processes. Macropores also exist in stream banks and have the potential to enhance the exchange of water and solutes between the channel and riparian groundwater, yet the geographic distribution of bank macropores is unknown. Here we determined the abundance, distribution, and geometry of naturally occurring surface-connected macropores in the banks of 20 streams across five physiographic provinces in the Eastern United States. We identified a total of 1,748 macropores, which were present in all 20 streams, with 3.8 cm average width, 3.3 cm average height, 11.5 cm average depth, and 27.9 cm average height above water surface elevation. Macropore abundance, distribution and geometry were statistically different between physiographic provinces, stream orders, and soil textures, with the latter being the most important. Macropores tended to be larger and more abundant in soils with a high cohesiveness and a low hydraulic conductivity compared to soils with a low cohesiveness and high hydraulic conductivity. As a result, streams with greater longitudinal heterogeneity of soil texture also had greater heterogeneity of macropore density. However, macropore size and height above baseflow water surface elevation also increased with stream order and therefore stream size. This work represents the first attempt to characterize macropores across a variety of riverine systems and presents evidence that macropores may play an important role in hyporheic exchange within stream banks. These results may have water quality implications, where macropores may enhance hyporheic exchange yet reduce the filtering capacity of riparian buffer zones. / MS / Preferential flow paths are soil cavities or areas of highly permeable porous media surrounded by media with a significantly lower permeability. Macropores are a type of preferential flow path where conduit-like voids in the subsurface are typically greater than three millimeters in diameter. Their formation is often the result of biological processes, such as animal burrows and plant roots, erosive action in subsurface flow, or cracks in the soil, and can enable rapid movement of water. Macropores are known to exist in stream banks and have the potential to enhance the exchange of water and solutes between the stream channel and riparian groundwater, yet the geographic distribution of bank macropores is unknown. This research examines the distribution, abundance, and geometry of naturally occurring macropores in the banks of 20 streams across five physiographic provinces in the eastern United States. Macropores were present in all 20 streams despite variations in physiographic province, stream order, and soil texture. However, soil texture appeared to have the greatest influence on the distribution, abundance, and geometry of macropores. For example, soils primarily containing silt and clay had more macropores than soils consisting of sand or gravel. We suspect this is due to differences in soil cohesiveness and/or hydraulic conductivity. This work represents the first attempt to characterize macropores across a variety of riverine systems and presents evidence that macropores may play an important role in surface water and groundwater exchange within stream banks. These results may have water quality implications, for example, how macropores affect the pollutant filtering capacity of riparian buffer zones.