Modelling sediment and total phosphorus export from a lowland catchment: comparing sediment routing methods

Bank erosion is the main source of suspended sediment (SS) and diffuse total phosphorus (TP) in many lowland catchments. This study compared a physically based sediment routing method (Physical method), which distinguishes between stream bed and bank erosion, with the original sediment routing method (Original method) within the Soil and Water Assessment Tool (SWAT) version 2009, for simulating SS and TP losses from a lowland catchment. A SWAT model was set up for the lowland River Odense catchment in Denmark and calibrated against observed stream flow and phosphate (PO₄) loads. On the basis of an initial calibration of hydrological and PO₄ parameters, the SWAT model with the Original method (Original model) and the SWAT model with the Physical method (Physical model) were calibrated separately against observed SS and TP loads. The SWAT model simulated daily stream flow well but underestimated PO₄ loads. The Physical model simulated daily SS and TP better than the Original model. The simulated contribution of bank erosion to SS in the Physical model (99%) was close to the estimated contribution from in situ erosion measurements (90–94%). Compared with the Original method, the Physical method is not only more conceptually correct but also improves model performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Estimating groundwater recharge in lowland watersheds

Little attention has been given to the role of groundwater in the hydrological cycle of lowland watersheds. Our objective in this study was to estimate total recharge to groundwater by analysing water table response to storm events and the rate at which water was transferred into the shallow aquifer. This was conducted at three sites in a rural watershed in the lower Atlantic coastal plain near Charleston, South Carolina, USA. A novel version of the water table fluctuation method was used to estimate total recharge to the shallow aquifer by comparing hourly data of water table position following storm events and measuring water table recession behavior, rather than subjective graphical analysis methods. Also, shallow aquifer recharge rates (vertical fluxes) were estimated using Darcy's Law by comparing static water levels in a water table well and in a shallow piezometer during dry periods. The total annual recharge estimated ranged from 107 ± 39 mm·yr^–1 (5–10% of annual precipitation) at a poorly drained topographic low area to 1140 ± 230 mm·yr^–1 (62–94% of annual precipitation) for a moderately well‐drained upland site. The average aquifer recharge rate was 114 ± 60 mm·yr^–1, which is similar to previous estimations of base flow for the ephemeral third‐order streams in this watershed. The difference in the two methods may have been caused by processes not accounted for in the Darcy flux method, soil moisture deficits, and average evapotranspiration demand, which is about 1100 mm·yr^–1 for this region. Although other factors also can affect partitioning of recharge, an integrated approach to inspecting easily gathered groundwater data can provide information on an often neglected aspect of water budget estimation. We also discuss the effects of land use change on recharge reduction, given a typical development scenario for the region. Copyright © 2011 John Wiley & Sons, Ltd.     

Fine‐grained bed sediment storage within the main channel systems of the Frome and Piddle catchments,Dorset, UK

Lowland permeable catchments in the UK are particularly prone to sedimentation problems, on account of the increased fine sediment loadings generated by recent land‐use change and their stable seasonal hydrological regimes, which are frequently depleted by groundwater abstraction. Fine‐grained sediment storage on the bed of the main channel systems of the Frome (437 km²) and Piddle (183 km²) catchments, Dorset, UK, has been examined at 29 sites using a sediment remobilization technique. Measurements encompassed the period February 2003–July 2004. At individual sites in the Frome, average values ranged between 410 and 2630 g m^?2, with an overall mean of 918 g m^?2. In the Piddle, the average values for individual sites varied between 260 and 4340 g m^?2, with an overall mean of 1580 g m^?2. Temporal variations in fine bed sediment storage at each site were appreciable, with the coefficients of variation ranging between 43 and 155% in the Frome and between 33 and 160% in the Piddle. Average reach‐scale specific bed sediment storage increased markedly downstream along each main stem from 2 to 29 t km^?1 (Frome) and from 4 to 19 t km^?1 (Piddle). Total fine sediment storage on the channel bed of the Frome varied between 479 t (5 t km^?1) and 1694 t (17 t km^?1), with a mean of 795 t (7 t km^?1), compared with between 371 t (5 t km^?1) and 1238 t (14 t km^?1) with a mean of 730 t (9 t km^?1) in the Piddle. During the study period, fine bed sediment storage was typically equivalent to 18% (Frome) and 57% (Piddle) of the mean annual suspended sediment flux at the study catchment outlets. Copyright © 2006 John Wiley & Sons, Ltd.     

面向防汛应急的重庆市洼地积涝预测模型研究

针对重庆市城市防汛应急的需要,在传统内涝模型的基础上,结合GIS空间分析与可视化技术,建立了一个运算快、实时性强的洼地积涝分析预测模型.该模型首先利用空间分析方法建立数字高程模型、城市洼地模型等数据模型,然后采用数值计算方法构建降雨模型、汇水模型、排水模型等分析模型,最后预测出洼地的积水面积、深度等.采用重庆市主城区的...     

Lowland Canterbury landscapes in the making

Abstract: This article explores environmental imaginaries of colonization in lowland Canterbury. In 1844 Edward Shortland observed that his Māori companions had an exceptionally detailed geographical knowledge of the area and its resources, yet a few years later European settlers were viewing it as an empty stage on which to envision newly‐constructed landscapes. The terrain was contested, but colonial ‘improvement’, through the creation of spaces of modernity, took no cognizance of this. The legacies of that transformation are a simplified, orderly landscape, and fractured but persistent memories of indigenous ecosystems that are now being revived.     

Impact of water transfer on interaction between surface water and groundwater in the lowland area of North China Plain

The contradiction between the freshwater shortage and the large demand of freshwater by irrigation was the key point in cultivated lowland area of North China Plain. Water transfer project brings fresh water from water resource‐rich area to water shortage area, which can in turn change the hydrological cycle in this region. Major ions and stable isotopes were used to study the temporal variations of interaction between surface water and groundwater in a hydrological year after a water transfer event in November 2014. Irrigation canal received transferred Yellow River, with 2.9% loss by evaporation during water transfer process. The effect of transferred water on shallow groundwater decreased with increasing distance from the irrigation canal. Pit pond without water transfer receives groundwater discharge. During dry season after water transfer event, shallow groundwater near the irrigation canal was recharged by lateral seepage and deep percolation of irrigation, whereas shallow groundwater far from irrigation canal was recharged by deep percolation of deep groundwater irrigation. Canal water lost by evaporation was 2.7–17.4%. Influence of water transfer gradually disappeared until March as the water usage of agricultural irrigation increased. In the dry season, groundwater discharged to irrigation canal and pond; 2.2–31.6% canal water and 11.3–20.0% pond water were lost by evaporation. In the rainy season (June to September), surface water was fed mainly by precipitation and surface run‐off, whereas groundwater was recharged by infiltration of precipitation. The two‐end member mix model showed that the mixing ratio of precipitation in pond and irrigation canal were 73–83.4% (except one pond with 28.1%) and 77.3–99.9%, respectively. Transferred water and precipitation were the important recharge sources for shallow groundwater, which decreased groundwater salinity in cultivated lowland area of North China Plain. With the temporary and spatial limitation of water transfer effects, increased water transfer amounts and frequency may be an effective way of mitigating regional water shortage. In addition, reducing the evaporation of surface water is also an important way to increase the utilization of transfer water.     

Dissolved oxygen criteria for freshwater fish in New Zealand: a revised approach

Maintenance of suitable conditions in lowland rivers for both fish passage and resident species is crucial to ensuring the long-term sustainability of fish populations. The dissolved oxygen concentration of water is a key factor controlling habitat quality for fish and a critical measure of stream health. Continued land use intensification and greater exploitation of water resources has contributed towards increasing the frequency and duration of low dissolved oxygen events in lowland rivers and the associated risk of adverse effects on fish communities. Revised guidelines are therefore proposed to support setting of biologically relevant dissolved oxygen limits for the protection of New Zealand freshwater fish communities. These guidelines account for both event magnitude and duration, identify different protection levels based on the risk of negative impacts and are based on current scientific knowledge on the tolerances of New Zealand fish species.     

AMS ^14C测年揭示的渤海湾沿海低地第Ⅱ海相层年龄

在渤海湾沿海低地地区获得4个机械钻孔,结合AMS 14C测年方法,对Ⅱ海的年龄进行了研究。结果显示,在Ⅱ海所在层位获得的14C样品年龄均大于43.5ka BP,说明渤海湾沿海低地地区Ⅱ海形成于MIS 3早期或MIS 5,而不是前人认为的23-39ka。建议在前人地层结构研究成果的基础上,系统开展Ⅱ海年龄研究。     

Temperature in lowland Danish streams: contemporary patterns,empirical models and future scenarios

Continuous temperature measurements at 11 stream sites in small lowland streams of North Zealand, Denmark over a year showed much higher summer temperatures and lower winter temperatures along the course of the stream with artificial lakes than in the stream without lakes. The influence of lakes was even more prominent in the comparisons of colder lake inlets and warmer outlets and led to the decline of cold‐water and oxygen‐demanding brown trout. Seasonal and daily temperature variations were, as anticipated, dampened by forest cover, groundwater input, input from sewage plants and high downstream discharges. Seasonal variations in daily water temperature could be predicted with high accuracy at all sites by a linear air‐water regression model (r²: 0·903–0·947). The predictions improved in all instances (r²: 0·927–0·964) by a non‐linear logistic regression according to which water temperatures do not fall below freezing and they increase less steeply than air temperatures at high temperatures because of enhanced heat loss from the stream by evaporation and back radiation. The predictions improved slightly (r²: 0·933–0·969) by a multiple regression model which, in addition to air temperature as the main predictor, included solar radiation at un‐shaded sites, relative humidity, precipitation and discharge. Application of the non‐linear logistic model for a warming scenario of 4–5 °C higher air temperatures in Denmark in 2070‐2100 yielded predictions of temperatures rising 1·6–3·0 °C during winter and summer and 4·4–6·0 °C during spring in un‐shaded streams with low groundwater input. Groundwater‐fed springs are expected to follow the increase of mean air temperatures for the region. Great caution should be exercised in these temperature projections because global and regional climate scenarios remain open to discussion. Copyright © 2006 John Wiley & Sons, Ltd.     

Water resources in mountain regions: a methodological approach to assess the water balance in a highland‐lowland‐system

Mountains and highlands are typically areas that provide considerable quantities of water, the latter being an important resource for the lowlands. These run‐off quantities remain discernible in the superior‐scale river systems and significantly contribute to the global water resources. Therefore, mountain regions ought to be given specific consideration with regard to management endeavours. Although well known in principle, details of water resources originating from mountains remain under discussion. A new approach has been introduced, which depicts the water balance of Switzerland in a spatially distributed manner, based on catchments of about 150 km². The main feature of this approach is the areal precipitation, which is calculated using run‐off, evaporation and storage change of glaciers, instead of being derived from gauged precipitation values. This methodology was selected because measurement and regionalization of precipitation remain subject to large uncertainties in mountainous areas. Subsequently, the view is widened to the European Alps, which, as compared with the surrounding lowlands, contribute considerably higher annual discharge, especially in the summer months. Finally, the focus is put on the hydrological significance of mountains in general. In dry regions, mountains, in particular, are indispensable contributors to the water resources downstream. Copyright © 2006 John Wiley & Sons, Ltd.