The role of landscape setting in minimizing hydrogeomorphic impacts of flow regulation

The Tongariro Power Development Scheme (TPDS) is used to regulate flow in the headwaters of the largest catchment on the North Island of New Zealand (the Waikato). Two small dams, the Rangipo Dam and the Poutu Intake Dam, were constructed in 1973 and 1983. The flow regime of the river is managed to divert freshes into the power scheme, but allows flows larger than 100 m³ s^?1 to be released, to rework and transport sediment through the catchment. Analysis of aerial photos and maps spanning 1928 to 2007, alongside field measurements, show that there have been few hydrogeomorphic adjustments since dam construction. This includes limited changes to channel geometry, channel planform and bed material organization immediately downstream of the dams. In addition, offsite effects are minimal, both 500 m downstream of each dam, and in the more sensitive, less confined reaches in the lower catchment (11 km downstream of the Poutu Intake dam). The limited changes can be attributed to the locations of the dams within reaches characterised by bedrock gorges and confined within terraces. These locations act to flush sediments and impose margins that allow minimal adjustment of the channel. Bed material within this reach is characterised by the presence of a boulder lag. This is sourced from long-term incision into lahar deposits, and acts to limit the rate of incision, creating a steep and stable base upon which active fractions are transported. Just as importantly, significant storage in the low-relief volcanic plateau located in the upper catchment acts to disconnect and store the high sediment yields generated by active volcanic cones in the western sub-catchment upstream of the dams. This limits the rate of sediment supply to regulated reaches. Findings from this study show that analysis of reach-scale controls is essential in framing dam site locations in relation to the distribution of reaches and landscape units across the catchment. In this instance, tributary inputs downstream of the dams do not replenish the sediment and flow removed at the dam locations, as has been observed in other regulated systems. Rather, the river itself is resilient to change and flow variability is well managed allowing geomorphically effective floods to occur. Landscape setting is a key consideration in determining the hydrogeomorphic impact of flow regulation.     

泰宁寨下大峡谷地学旅游资源及科学价值

泰宁寨下大峡谷由悬天峡、通天峡和祈天峡3条峡谷构成,地貌景观优美、生态环境优良、地学旅游资源丰富,是泰宁山原-峡谷型青年期丹霞地貌的典型代表,峡谷中丹崖高耸,洞穴密布,线谷纵横,地质遗迹众多,科学内涵丰富,集中展示了丹霞线谷、巷谷及洞穴发育演化。经科学规划和精心建设,现已成为泰宁世界地质公园开展丹霞地貌科考、科普、地学与生态旅游的主要线路。     

县域土地利用景观格局变化研究——以陇县为例

依据景观生态学基本原理,应用spss软件、arcgis软件和景观格局分析软件Fragstates对陇县1989～2009年土地利用景观格局的变化和空间分布进行研究,并根据各景观类型的景观格局指数计算结果对该区土地利用景观格局进行分析评价。结果表明,陇县主要景观类型为林地、耕地和草地,林地和建设用地保持稳定而迅速增长,草地和未利用地呈现逐渐减少趋势;人类活动使水域、未利用地更为分散,建设用地、园地更为集中;景观多样性降低,破碎化程度减缓,斑块形状的复杂程度并未发生大幅度的变化,人类活动对景观格局的影响保持在一定范围内。     

Progressive landscape fragmentation in relation to cash crop cultivation

Cash crop cultivation has been a critical driver of land use change in many countries around the world. However, few efforts have been made to quantify the relationships between cash crop expansion and the subsequent landscape pattern changes. This paper characterized the process of cash crop expansion across Tiaoxi watershed (China) from 1985 to 2009 using multi-sensor and multi-temporal remotely sensed imageries. Correlations were identified between indicators of cash crop expansion (total area and total production of cash crops) and a family of landscape fragmentation metrics (patch density, edge density, landscape division index, effective mesh size, splitting index, Shannon's diversity index, and aggregation index). Results showed that Tiaoxi watershed experienced profound cash crop expansion and progressive landscape fragmentation. The cash crops spread in accessible and productive areas at the expense of paddy and forests. Social drivers of cash crop expansion included population growth, labor structure changes and market incentives. Indicators of cash crop expansion presented linear relationships with landscape fragmentation metrics. These findings evidenced that cash crop cultivation would significantly fragment landscapes. Our study contributed to understanding on the enlarging cultivation of cash crops and the associated modifications of landscape patterns in subtropical regions.     

基于遥感和GIS的海岸带水域生态景观格局演变研究——以杭州湾北岸上海市段为例

以杭州湾北岸上海市段为例,利用谱间关系法从多时相遥感影像中提取出1992年、2001年和2008年的水域信息,通过水域斑块数量、面积、密度、形状、分维数和景观动态度等分析其动态变化; 利用GIS空间分析方法绘制了水域密度的空间分布图.结果显示,由于受人类活动的干扰,16 a来杭州湾北岸上海段水域景观格局发生了显著变化,...     

Erosion surfaces and Neogene landscape evolution in the NE Duero Basin (north-central Spain)

We present a chronological model of erosion surface development in the Iberian and Cantabrian Ranges of north-central Spain. We map four erosion surfaces and interpret these to be related to Duero basin continental sediments and tectonic activity from Upper Oligocene to Plio-Pleistocene. The oldest erosion surface, SE1, formed across Upper Oligocene–Lower Miocene synorogenic deposits; while surface SE2 was contemporaneous with the Middle Miocene alluvial systems, ending with an uplift stage in the Astaracian. The two most recent erosion surfaces, SE3 and SE4, developed during extensional tectonic episodes and are associated with the deposition of Upper Páramo sedimentary units at the end of the Miocene (Upper Turolian) and alluvial fan deposits, known as rañas (Plio-Pleistocene). With the exception of SE1, which seems to be associated with a relatively wet climate, the surfaces formed during periods of marked aridity and generally warm temperatures. Through geostatistical reconstruction of the best preserved surface (SE2), applying ordinary kriging method to the topography (DEM) of the erosion surface and its correlating sedimentary plains, we identify the deformation processes which occurred on this surface after its formation.     

Crossing the divide: Representation of channels and processes in reduced-complexity river models at reach and landscape scales

Reduced-complexity models have considerable potential as tools for elucidating river behaviour over periods of 10⁰–10⁴ years and, consequently, for addressing fundamental questions concerning the scale-dependent nature of explanation in geomorphology. This paper proposes a simple subdivision of reduced-complexity models of river behaviour into two categories that mirror methodological developments in fluvial geomorphology over the past 50 years. First, high-resolution cellular approaches that are implemented within a framework that resolves process-form feedbacks at small time and space scales. Second, models that incorporate section-averaged representations of channel geometry and processes, and that are typically underpinned by regime theory and equilibrium concepts. Examples of both model types are presented here, in the form of a cellular representation of stream braiding and a combined lattice-network model of alluvial fan evolution. Simulations conducted using these models demonstrate how small-scale process-form interactions determine the emergence of larger-scale channel and fan morphology and, in so doing, regulate system response to external forcing. In this sense, both models demonstrate that internal feedbacks play a critical role in controlling river responses to environmental change over historic and Holocene timescales. However, both classes of model are characterised by uncertainty in their parameterisation of geomorphic processes, such that internal feedbacks and thresholds for channel response to external forcing may vary substantially between competing models. Methods of refining both approaches are considered, and hybrid models based on lattice-network structures and mechanistic representations of channel process-form interactions are identified as a means of addressing the shortcomings of existing strategies.     

Scaling in river corridor widths depicts organization in valley morphology

Landscapes have been shown to exhibit numerous scaling laws from Horton's laws to more sophisticated scaling in topography heights, river network topology and power laws in several geomorphic attributes. In this paper, we propose a different way of examining landscape organization by introducing the “river corridor width” (lateral distance from the centerline of the river to the left and right valley walls at a fixed height above the water surface) as one moves downstream. We establish that the river corridor width series, extracted from 1 m LIDAR topography of a mountainous river, exhibit a rich multiscale statistical structure (anomalous scaling) which varies distinctly across physical boundaries, e.g., bedrock versus alluvial valleys. We postulate that such an analysis, in conjunction with field observations and physical modeling, has the potential to quantitatively relate mechanistic laws of valley formation to the statistical signature that underlying processes leave on the landscape. Such relations can be useful in guiding field work (by identifying physically distinct regimes from statistically distinct regimes) and advancing process understanding and hypothesis testing.     

基于手持GPS洞庭湖区植被景观格局外业调绘研究

本文以1∶50 000的地形图为工作底图,采用手持GPS技术、利用实地调查与分解森林资源分布图相结合的方法,对洞庭湖区植被分布状况进行了外业调绘的研究。建立了外业调绘过程中植被群落斑块最小面积和边界的确定原则及其斑块类型与编码。探讨了手持GPS实现WGS-84坐标系向1954北京坐标系的转化方法,并进行了精度估算,其点位误差≤5.8 m,完全可以满足洞庭湖区植被分布外业调绘的精度要求。运用该方法进行植被分布的外业调绘,可以解决运用传统的定位测量方法在湖区定位难的问题,提高了外业作业效率。     

Boulder weathering and erosion associated with a wildfire, Sierra Ancha Mountains, Arizona

An April–May 2000 “Coon Creek Fire” burned 37.5 km² of the Sierra Ancha Mountains, 32.3 km miles north of Globe, AZ—including 25 sandstone and 19 diorite boulders surveyed in 1989 and resurveyed after the burn, after the summer 2000 monsoon season, and after the winter 2001 season. When viewed from the perspective of cumulative eroded area, both sandstone and diorite displayed bimodal patterns with 79% of sandstone boulder area and 93% of diorite boulder area undergoing either no fire-induced erosion or fire-induced erosion >76 mm. When stretched over cumulative boulder areas, erosion due to the fire averaged >26 mm for sandstone and >42 mm for diorite. Post-fire erosion from thunderstorm summer rains averaged <1 mm for 5 diorite and 1 mm for 10 sandstone boulders. While only a single diorite boulder eroded an average of 1.2 mm after the winter, winter erosion removed an average of 5.5 mm from 14 sandstone boulders. Thus, fire appears to increase a rock's susceptibility to post-fire weathering and erosion processes, as predicted by Goudie et al. [Earth Surf. Process. Landf. 17 (1992) 605]. In contrast to experimental research indicating the importance of size in fire weathering, no statistically significant relationship exists between erosion and boulder height or boulder surface area—a result similar to Zimmerman et al. [Quat. Res. 42 (1994) 255]. These data exclude 12 original sites and 85 boulders at sites impacted by the fire that could not be relocated, with a reasonable cause for the lack of relocation being boulder obliteration by the fire. Given evidence from ¹⁰Be and ²⁶Al cosmogenic nuclides [Earth Planet. Sci. Lett. 186 (2001) 269] supporting the importance of boulders in controlling evolution of nonglaciated, bouldered landscapes [Geol. Soc. Amer. Bull. 76 (1965) 1165], fire obliteration of boulders could be an important process driving drainage evolution in nonglaciated mountains.