Benchmarking land use change impacts on direct runoff in ungauged urban watersheds

This paper describes the results of benchmark testing of land use change impact on direct runoff using Soil Conservation Service-Curve Number (SCS-CN) model in two ungauged neighbouring urban watersheds (Çınar and Kadıyakuplu) in Istanbul, Turkey. To examine this impact, the model was applied to daily rainfall data using three different dated (1982, 1996 and 2012) hydrological soil groups and land use of the two ungauged urban watersheds. Finally, the impact of land use change and model performance were evaluated with the rainfall-runoff regression, the coefficient of determination and the NSE test using benchmark runoff data based on 1982 land use conditions. The results of the analysis indicate that the changing of land use types from natural surfaces to impervious surfaces has a significant impact on surface runoff. Additionally, remarkable spatial variations of the land use changes and their impact on the runoff in 1996 and 2012 were more detected in the Çınar watershed compared with the Kadıyakuplu watershed. The planning decision on land use of the watersheds, has vital role in these differences. The results of this research also reveal that change to intensive land use in urban watersheds has a significantly larger impact on runoff generation than those rainfall.     

Effects of micro-topography on surface–subsurface exchange and runoff generation in a virtual riparian wetland — A modeling study

In humid upland catchments wetlands are often a prominent feature in the vicinity of streams and have potential implications for runoff generation and nutrient export. Wetland surfaces are often characterized by distinct micro-topography (hollows and hummocks). The effects of such micro-topography on surface–subsurface exchange and runoff generation for a 10 by 20 m synthetic section of a riparian wetland were investigated in a virtual modeling experiment. A reference model with a planar surface was run for comparison. The geostatistically simulated structure of the micro-topography replicates the topography of a peat-forming riparian wetland in a small mountainous catchment in South-East Germany (Lehstenbach). Flow was modeled with the fully-integrated surface–subsurface code HydroGeoSphere. Simulation results showed that the specific structure of the wetland surface resulted in distinct shifts between surface and subsurface flow dominance. Surface depressions filled and started to drain via connected channel networks in a threshold controlled process, when groundwater levels intersected the land surface. These networks expanded and shrunk in a spill and fill mechanism when the shallow water table fluctuated around the mean surface elevation under variable rainfall inputs. The micro-topography efficiently buffered rainfall inputs and produced a hydrograph that was characterized by subsurface flow during most of the year and only temporarily shifted to surface flow dominance (> 80% of total discharge) during intense rainstorms. In contrast the hydrograph in the planar reference model was much “flashier” and more controlled by surface runoff. A non-linear, hysteretic relationship between groundwater level and discharge observed at the study site was reproduced with the micro-topography model. Hysteresis was also observed in the relationship between surface water storage and discharge, but over a relatively narrow range of surface water storage values. Therefore it was concluded that surface water storage was a better predictor for the occurrence of surface runoff than groundwater levels.     

A process-based,distributed hydrologic model based on a large-scale method for surface–subsurface coupling

Process-based watershed models are useful tools for understanding the impacts of natural and anthropogenic influences on water resources and for predicting water and solute fluxes exported from watersheds to receiving water bodies. The applicability of process-based hydrologic models has been previously limited to small catchments and short time frames. Computational demands, especially the solution to the three-dimensional subsurface flow domain, continue to pose significant constraints. This paper documents the mathematical development, numerical testing and the initial application of a new distributed hydrologic model PAWS (Process-based Adaptive Watershed Simulator). The model solves the governing equations for the major hydrologic processes efficiently so that large scale applications become relevant. PAWS evaluates the integrated hydrologic response of the surface–subsurface system using a novel non-iterative method that couples runoff and groundwater flow to vadose zone processes approximating the 3D Richards equation. The method is computationally efficient and produces physically consistent solutions. All flow components have been independently verified using analytical solutions and experimental data where applicable. The model is applied to a medium-sized watershed in Michigan (1169 km²) achieving high performance metrics in terms of streamflow prediction at two gages during the calibration and verification periods. PAWS uses public databases as input and possesses full capability to interact with GIS datasets. Future papers will describe applications to other watersheds and the development and application of fate and transport modules.     

Control Volume Method for the Dynamo Problem in the Sphere with the Free Rotating Inner Core

A model of thermally driven dynamo in the Boussinesq approximation in the spherical shell with the free rotating inner core is considered. To solve equations we use a new in dynamo modeling control volume technique (for details of this method for hydrodynamics see Patankar, 1980). The main advantage of this method over previous attempts to solve magnetohydrodynamics equations in the spherical grids is that no filtering of high harmonics in the pole regions is needed. We present the results of simulations for the self-consistent dynamo system evolution over the diffusion time and longer periods. Different ways of stabilizations of magnetohydrodynamics equations, when convective terms are of the same order (or larger) as conductive ones, are considered.     

Modelling pipeflow contributions to stream runoff

Runoff from natural soil pipes has been shown to be a significant contributor to stream discharge in parts of upland Wales. Attempts have been made to model pipeflow contributions using both theoretical and empirical approaches, but little progress has yet been made towards producing generally applicable models of complete pipeflow systems. The paper identifies some of the problems of devising general models with reference to data from the Maesnant Experimental Catchment. The data suggest that in-pipe travel times are more important here than inferred elsewhere, and that neither simple hydraulic models nor kinematic wave theory can adequately explain the patterns of response. In particular, stormflow tends to begin first at the network outfall and even peak discharge often occurs at the outfalls before the headward zones.     

Soil erosion and overland flow in forested areas with pine plantations at coastal mountain range,central chile

The effects of timber-cutting on sediment concentrations, soil loss and overland flow in an insigne pine (Pinus radiata) plantation were studied in a mountain watershed of the Cordillera de la Costa, central Chile. Soil formation rates for the lithological conditions of the watershed were estimated. Soil loss measurements on the plantation were taken in 100 m² plots, equipped with Coshocton samplers, during the years 1991 and 1992. Treatments were: clear-cutting no residues/burned, clear-cutting with residues and undisturbed controls. First-year soil losses were greater from the no residues/burned (2128 kg ha^?1) than from the residues (1219 kg ha^?1) or undisturbed (48 kg ha^?1) plots. During the second post-treatment year, soil loss was greater from the burned plots (1349 kg ha^?1) than from the residues (243 kg ha^?1) or the undisturbed (72 kg ha^?1) plots. Sediment concentrations for the three treatments were 561, 340 and 59 mgl-¹ during the first year, and 400, 150 and 83 mgl^?1 in the second year. Runoff from the no residues/burned plots was greater than from residues or undisturbed plots during the two post-treatment years. Long-term soil losses were projected to average 240 kg ha^?1 yr^?1 from areas without residues/burned and 120 kg ha^?1 yr^?1 in areas with residues treatment, over a 25 year rotation period, whereas control areas were projected to average 60 kg ha^?1 yr^?1.     

黄土高原小流域特性指标与产沙统计模式

本文从黄土高原实际情况出发，在广泛的野外考察基础上，收集了面积在0．193--329km2的58个小流域(包括21个变量)的系列数据。通过分析筛选，建立了流域地表综台特性指标：     

Analysis of the mobilization of solid loads and heavy metals in runoff waters from granite quarries

The cutting operations of dimension stone at quarries produce a large amount of fines that, in turn, cause a negative environmental impact over local surface waters. This article presents a detailed analysis of the mobilized contamination associated with runoff waters in a large granite quarry (～200 ha) which is located in Porriño (Galicia, NW Spain), the most important production centre of dimension stone in Spain. There, an intensive monitoring survey was developed in order to characterize the hydrology of the system as well as the release and transport of pollutants. This was accomplished by means of different control sections for the flow and by the collection of 52 random water samples. Automatic samplers were also used to collect 192 water samples associated with runoff generated by significant rain events. For each of the samples collected, a wide battery of analytic determinations was performed, including solid loads, turbidity, organic pollution, nutrient and selected metals. Upon careful examination it has been possible to obtain different parameters related to the contamination control, like the “event mean concentration” (EMC), maximum concentrations and specific sediment loads. Moreover, a comprehensive statistical study including parameter correlation and cumulative probability analyses helped to understand the pollutant mobilization behaviour within the quarry system. It can be concluded that mobilized contamination shows the anomalous presence of some metals, whose concentrations are in excess when compared to the natural rock. This excess metal amount must be attributed to an anthropogenic source associated to mining and cutting operations.