贺兰山水系流域数值地貌特征及其构造指示意义

基于Arcgis9.3与ASTER GDEM数据,提取了贺兰山两侧主要水系及其流域边界,根据河流及流域指标提取河流纵剖面、流域的Strahler曲线,并计算其面积高度积分值（Hypsometric Intergral）、河流纵剖面的凹度值（Concavity）。通过HI值、凹度值同河流落差、河流长度、流域面积之间相关性分析发现,后3种地貌参数与HI值、凹度值间的相关性较差。对比分析贺兰山两侧河流HI值及凹度值发现：贺兰山东侧北段活动性大于南段,西侧构造活动性分布规律不明显。结合9条河流所处流域的Strahler曲线、河流纵剖面形态和HI值、凹度值分析发现：汝箕沟及其以北贺兰山地区处于地形演化的老年期,汝箕沟以南贺兰山段处于均衡调整的壮年期。     

六棱山北麓中段冲沟地貌发育的定量研究及其新构造意义

利用地貌形态指标对六棱山北麓断层中段的5条冲沟进行定量化研究,流域的冲沟比降指标(SL)、面积--高度积分值(HI)和流域盆地形态因子(Bs)的异常值表明5条冲沟的发育对六棱山北麓断层活动性有明显的响应,流域发育处于壮年期.秋林沟口野外实测数据验证并揭示了六棱山北麓断裂晚第四纪以来的活跃性.     

格尔木河流域面积-高程积分值的地貌学分析

在sRTM-DEM数据的基础上,运用GIS空间分析技术,系统提取了格尔木河三级流域及部分二级流域地形参数和面积-高程积分值,探讨了面积-高程积分值的面积及空间依赖性,并对面积-高程积分值(HI)对构造活动性、岩性变化、冰川作用强度的指示意义进行了研究.研究表明:HI值具有面积依赖及空间依赖性;东昆南断裂(F4)-西大滩断裂(F3)以昆仑山口为界可以分为东西两部分,各自的活动性都是中间强往两边依次减小,东昆中断裂(F1)的活动性变化不大;岩性对HI影响表现出,侵入岩的抗侵蚀力最大,片岩的抗侵蚀力最小,碳酸盐岩组合的抗侵蚀力居中;冰川作用对地貌发育和侵蚀程度有改造作用,与只有古冰川发育或无古冰川流域比较,有现代冰川发育,古冰川作用遗迹广泛的流域,HI值较大并会出现U型谷.     

面积高度积分的面积依赖与空间分布特征

面积高度积分作为揭示区域构造相对活动性的指标,其面积依赖和空间分布两大特性会影响到它对构造活动的解释。以北天山10条河流流域作为研究区域,研究表明,在不同集流面积阈值下,天山北麓流域次集水盆地的平均面积高度积分与平均面积、平均高差都具有负相关关系。受北天山褶皱逆断裂构造带的影响,流域面积高度积分值的分布与构造带走向相一致,上游山地型次集水盆地面积高度积分值大于中游山麓丘陵型次集水盆地面积高度积分,揭示了面积高度积分存在空间分布依赖的特性。在大小不同观测尺度下,构造活动和基岩岩性差异对面积高度积分有着不同的影响。在玛纳斯河流域中,以不同集流阈值提取的不同面积大小的次集水盆地与各年代地层以及活动构造做GIS叠加分析,可以发现当集流阈值小于9km²时,面积高度积分值受到岩性与构造的双重影响,而当集流阈值大于20km²时,面积高度积分值主要反映构造活动的影响。     

Tectonic constraints on watershed development on frontal ridges: Mohand Ridge, NW Himalaya, India

Uplifting frontal ridges are one of the most conspicuous geomorphic features that mark the frontal parts of actively converging mountain belts. Growth of these ridges can lead to the simultaneous development of a drainage system that is defined by watersheds, stream network and long profiles of channels. In the present study, shape parameters of watersheds, stream network characteristics and pattern of network growth, shape of long profiles, and the SL index have been investigated in a part of NW Himalaya to understand the relationship between endogenic tectonic processes and exogenic fluvial processes. This explains the tectonic control on drainage systems in the uplifting frontal ridge. This watershed analysis was carried out using a Digital Elevation Model (DEM) and a number of anomalies have been identified and analysed. The most striking is the asymmetric development of watersheds on either side of an almost straight ridge crest. Watershed asymmetry along the ridge crest is characterized by larger area and less elongated watersheds in the southern flank (forelimb) in comparison to the northern flank (backlimb). Drainage network and long profile analysis establishes that the larger watershed area in the forelimb is due to dominance of headward erosion and its impact on drainage network growth. Dominance of headward erosion is due to slope variation in response to forelimb development along a fault-related fold. Even through, headward erosion has shifted the ridge crest; it is parallel with the trace of the Himalayan Frontal Thrust (HFT). The parallel ridge crest with reference to the HFT is indicative of the tectonic control of the HFT on the development of the watersheds. Hence, a well developed linkage between tectonic processes (fold development) and surface processes (headward erosion) is responsible for variation in watershed and drainage network pattern across the ridge crest. The study also investigates the role of planform ridge curvature on watershed development. The effect is more pronounced on an asymmetric ridge, such as the Mohand ridge, than on a symmetric ridge.     

The Pinjaur dun (intermontane longitudinal valley) and associated active mountain fronts, NW Himalaya: Tectonic geomorphology and morphotectonic evolution

The Himalayan orogenic belt, formed as a result of collision tectonic processes, shows abundant evidence of neotectonic activity, active tectonics, and the occurrence of historical earthquakes. Its frontal deformation zone is characterized, in some segments, by intermontane longitudinal valleys (duns). Such frontal segments of the Himalaya are marked by the occurrence of multiple mountain fronts.In one such segment of the foothills of the NW Himalaya, the Pinjaur dun is developed and marked by three mountain fronts: MF1A and MF1B associated with the southernmost Himalayan Frontal Thrust (HFT), MF2 associated with the Sirsa fault, and MF3 associated with the Barsar thrust along the southern margin of the relatively higher main part of the sub-Himalaya. Geomorphic responses to the tectonic activity of these and related structural features have been analyzed through the use of geomorphic indices, drainage density, stream longitudinal profiles, drainage anomalies, and hypsometric analysis. Also, fault and fold growth and their expression on landform development was studied using a combination of surface profiles and field observations.The values of valley floor width to height ratio (V_f) for valleys associated with MF1 ranged between 0.07 and 0.74, and for valleys associated with MF2 ranged from 1.02–5.12. V_f for the four major valleys associated with MF1B ranged from 1.1–1.7. The asymmetry factor for 26 drainage basins related to MF1A indicate these have developed under the influence of a transverse structure. These results taken together with those obtained from the Hack profiles and SL index values, hypsometry, drainage density, and drainage anomalies suggest that the faults associated with the mountain fronts and related structures are active.Active tectonics and neotectonic activity have led to the formation of four surfaces in the Pinjaur dun. In addition, an important drainage divide separating the Sirsa and Jhajara drainage networks also developed in the intermontane valley. Surface profile analysis helped in deciphering the growth history of the fault bend fold structures of the outermost Siwalik hills. The effects of tectonic activity on the proximal part of the Indo-Gangetic plains are interpreted from the remarkable river deflections that are aligned linearly over tens of kilometers in a zone about 10 km south of the HFT.Based on these integrated structural and tectonic geomorphological approaches, a morphotectonic evolutionary model of the dun has been proposed. This model highlights the role of uplift and growth history of the fault bend fold structures of the outermost Siwalik hills on (i) the depositional landforms and drainage development of the Pinjaur dun, and (ii) valley development of the outermost Siwalik hills.Importantly, this study postulates the formation of an incipient mountain front that is evolving ahead of the HFT and the outermost Siwalik hills in the Indo-Gangetic plains.     

A STREAM-GRADIENT INDEX APPLIED TO SUBHUMID MONTANE STREAMS

Hack (1973) introduced the stream-gradient index as a measure to analyze longitudinal stream profiles. It is derived from the channel slope at a point and channel length as measured along the longest stream above that point. In the eastern United States, empirical evidence shows the stream-gradient index to be a rough approximation of stream power or competence. Validity of this relationship in other geomorphic and climatic regions was unproven. Eight canyon drainages in the Bear River Range, north-central Utah, provide a basis for testing the validity of stream-gradient index analysis in a subhumid montane area. These drainages are found to have a drainage area to discharge function, rate of increase in channel width downstream, and coverging stream network with an average length proportional to a power of the drainage similar to Hack's original study area. These similarities indicate that use of stream-gradient indices as approximations of stream power are valid in subhumid montane areas. Stream-gradient index analysis of canyon streams in the Bear River Range illustrates drainage adjustment to tectonic activity, bedrock lithology, and structural attitude.     

中条山北麓河流地貌参数及其新构造意义

基于数字高程模型（DEM）及地理信息系统（GIS）技术,系统提取和分析了中条山北麓河流坡降指标、河道陡峭指数及面积高程积分等河流地貌参数。研究表明：河流坡降指标、河道陡峭指数及面积高程积分在永济至解州一带表现出较高的值;综合分析岩性、降水及构造等因素可知,新构造运动是控制中条山北麓河流地貌发育的主要因素,自北向南总体表现出增强的趋势,在永济南活动最强。前人研究表明,中条山北麓断裂晚第四纪以来构造活跃,全新世以来仍有多次活动,但不同部位活动强度各异,解州段晚更新世晚期以来滑动速率相比韩阳段及夏县段高,极高值在出现在永济南一带。可见,基于河流地貌参数获得的中条山北麓新构造运动强弱与断裂晚第四纪以来的活动强弱一致。     

The sensitivity of East African rift lakes to climate fluctuations

Sequences of paleo-shorelines and the deposits of rift lakes are used to reconstruct past climate changes in East Africa. These recorders of hydrological changes in the Rift Valley indicate extreme lake-level variations on the order of tens to hundreds of meters during the last 20,000 years. Lake-balance and climate modeling results, on the other hand, suggest relatively moderate changes in the precipitation-evaporation balance during that time interval. What could cause such a disparity? We investigated the physical characteristics and hydrology of lake basins to resolve this difference. Nine closed-basin lakes, Ziway-Shalla, Awassa, Turkana, Suguta, Baringo-Bogoria, Nakuru-Elmenteita, Naivasha, Magadi-Natron, Manyara, and open-basin Lake Victoria in the eastern branch of the East African Rift System (EARS) were used for this study. We created a classification scheme of lake response to climate based on empirical measures of topography (hypsometric integral) and climate (aridity index). With reference to early Holocene lake levels, we found that lakes in the crest of the Ethiopian and Kenyan domes were most sensitive to recording regional climatic shifts. Their hypsometric values fall between 0.23–0.29, in a graben-shaped basin, and their aridity index is above unity (humid). Of the ten lakes, three lakes in the EARS are sensitive lakes: Naivasha (HI = 0.23, AI = 1.20) in the Kenya Rift, Awassa (HI = 0.23, AI = 1.03) and Ziway-Shalla (HI = 0.23, AI = 1.33) in the Main Ethiopian Rift (Main Ethiopian Rift). Two lakes have the graben shape, but lower aridity indices, and thus Lakes Suguta (HI = 0.29, AI = 0.43) and Nakuru-Elmenteita (HI = 0.30, AI = 0.85) are most sensitive to local climate changes. Though relatively shallow and slightly alkaline today, they fluctuated by four to ten times the modern water depth during the last 20,000 years. Five of the study lakes are pan-shaped and experienced lower magnitudes of lake level change during the same time period. Understanding the sensitivity of these lakes is critical in establishing the timing or synchronicity of regional-scale events or trends and predicting future hydrological variations in the wake of global climate changes.     

Differential effect of neotectonic process on stream characteristics: a geomorphologic evaluation of the Meenachil River basin,Kerala, India

Morphotectonic characteristics of the Meenachil River and its major tributaries in Kerala, India, were evaluated to understand the effects of tectonic processes on stream characteristics. Parameters such as longitudinal profile, stream length-gradient index (SL index), SL anomaly index, and transverse topographic symmetry factor (T) were considered. Longitudinal profiles of all the rivers show convexity and knickpoints in the segments between the headwaters and middle reaches, and further follow smooth profiles. Anomalies in longitudinal profiles were confirmed by the relatively high SL indexes. The SL anomaly index categorizes stream segments based on the severity of anomalies. The T index indicates the differential effect of tectonic processes in the river basin and in channel characteristics by showing spatial variation in its magnitude and orientation. Variations in the SL index, SL anomaly index, and T index in rivers flowing through similar lithology confirm the influence of differential effects of tectonic processes over the stream and networks and the nonequilibrium condition of the Meenachil River basin as a single unit.     

Development and morphometry of drainage network in volcanic terrain, Central Anatolia, Turkey

This paper presents the results of morphotectonic and morphometric research carried out in order to determine the neotectonic development of the volcanic mountains and a drainage network in SW Cappadocia. The study area extends among the Aksaray, Ni?de, and Nev?ehir Provinces. The study area comprises Hasanda?, Melendiz, Keçiboyduran, Göllüda? Mountains and the adjacent parts of these volcanic mountains.Data collected exclusively from 1:25,000 digitised topographic maps and 10 m-resolution DEMs were used to define parameters related to the longitudinal profile of streams. The study area was divided into 10 volcanic units. Longitudinal profiles of 20 streams and stream orders were analysed to determine a regional tectonic differentiation pattern in these units. The streams in the study area drain into four different tectonic depressions. These depressions are Aksaray plain controlled by the Tuz Gölü fault (TGF), Çiftlik plain controlled by the Keçiboyduran–Melendiz fault (KMF), Misli plain controlled by the Derinkuyu fault (DF), and Bor plain controlled by the Ni?de Fault Zone (NFZ). An analysis of morphometric parameters shows that the development of a drainage network is associated with faults and rock resistance. Occurrence of morphometric parameters with different values in units reveals that the volcanic mountains were not uplifted in the same period and were subjected to different morphologic processes. High total order number in the south of Hasanda? (unit 3) and Melendiz Mountains (unit 7) indicate that the uplift ratio of the southern part is much greater than that of the northern part. Moreover, development of the drainage network in the south is in a more advanced phase than in the north. Indeed, the drainage network in the north is in the youngest erosional phase of all parts of the study area. The increased stream length-gradient indices (SL), and stream gradients and an analysis of headward erosion show that the streams displaying the longest and highest reach of the erosional phase are all in the southern part of Keçiboyduran and Melendiz Mountains. The longitudinal profile (Lp) of the present thalweg of the streams is irregular. The irregular Lp are associated with four different causes. These are geological variations in resistance, tectonics, and volcanic topography and downcutting in response to stream incision. The beginning of the fluvial incision in the northern part is younger than in the south.     

Paleolimnological investigations of anthropogenic change in Lake Tanganyika: VIII. Hydrological evaluation of two contrasting watersheds of the Lake Tanganyika catchment

This study was conducted to delineate the impact of human activities on stream flow and water chemistry as well as other factors that influence the chemical character of both surface and groundwater in two contrasting watersheds of the Lake Tanganyika catchment. The study sites the Mwamgongo and Mitumba streams along the northern Tanzanian coastline of the lake are representative of disturbed and undisturbed watersheds, respectively, but are quite similar in other characteristics of slope, bedrock geology and size. Separation of stream flow components was undertaken using classical hydrograph analysis along with chemical methods using both Cl and ¹⁸O data. All the data show that groundwater accounts for the predominant source of total stream flow in both the Mwamgongo and Mitumba watersheds (65 and 70% respectively). The streams have an average ¹⁸O of about -3.0% and less than 10 mg/l for Cl. The basin recession constants of 9.4×10^-3-d^-1 and 9.6×10^-3-d^-1 for Mwamgongo and Mitumba, respectively, indicate existence of both fissured and fractured aquifer systems. The chemical data exhibit low values of all determined ions. This supported the hypothesis that natural processes influence the water chemical character of the study area. An Mg–HCO₃ type of water dominates in the two watersheds. Despite their similar size and bedrock character the Mwamgongo watershed has an order of magnitude in sediment transport than the Mitumba one. The data show that the disturbed watershed discharges less groundwater and more sediments, and has a poorer water quality than the forested Mitumba watershed, which lies within the Gombe National Park. The data show that soil erosion processes are more active at Mwamgongo, and that both the surface runoff component of the total stream flow and increased dissolved salt load is greater in the deforested Mwamgongo watershed than in the Mitumba watershed. The chloride and ¹⁸O data complemented each other in delineating the amounts of groundwater in the total stream flow as the results using both data differed insignificantly. It may be concluded that the undisturbed watershed has a higher retention of good quality water and traps more sediments than the disturbed one. In addition, the groundwater component plays a dominant role in the total annual stream flow at each watershed.     

A Review of “Tectonic Faults: Agents of Change on a Dynamic Earth”

The fluvial system represents a nested hierarchy that reflects the relationship among different spatial and temporal scales. Within the hierarchy, larger scale variables influence the characteristics of the next lower nested scale. Ecoregions represent one of the largest scales in the fluvial hierarchy and are defined by recurring patterns of geology, climate, land use, soils, and potential natural vegetation. Watersheds, the next largest scale, are often nested into a single ecoregion and therefore have properties that are indicative of a given ecoregion. Differences in watershed morphology (relief, drainage density, circularity ratio, relief ratio, and ruggedness number) were evaluated among three ecoregions in eastern Oklahoma: Ozark Highlands, Boston Mountains, and Ouachita Mountains. These ecoregions were selected because of their high-quality stream resources and diverse aquatic communities and are of special management interest to the Oklahoma Department of Wildlife Conservation. One hundred thirty-four watersheds in first- through fourth-order streams were compared. Using a nonparametric, two-factor analysis of variance (α= 0.05) we concluded that the relief, drainage density, relief ratio, and ruggedness number all changed among ecoregion and stream order, whereas circularity ratio only changed with stream order. Our study shows that ecoregions can be used as a broad-scale framework for watershed management.     

Hypsometric Analysis of Headwater Rock Basins in the Dolomites (Eastern Alps) Using High‐Resolution Topography

Hypsometric curves and integrals are effective tools for rapid quantitative assessments of topography. High‐resolution digital terrain models derived from airborne LiDAR data have been analysed to study the hypsometry of small headwater rock basins (drainage areas up to 0.13 km²) in three study areas in the Dolomites (Eastern Alps) that have similar lithologies and climatic conditions. Hypsometric curves in the studied rocky headwaters display a variety of shapes and present remarkable differences between neighbouring basins. Hypsometric integrals show generally high values in the three study areas (>0.42, mean values between 0.51 and 0.65). The extent of the scree slopes located at the foot of rock basins in the three study areas is larger in the area with lower hypsometric integrals and indicates consistency between the development of basin erosion, which is shown by the hypsometric integral, and debris yield, represented by the extent of scree slope. No clear relations were observed between the hypsometric integrals and basin area and shape. When extending the analysis to larger basins, which encompass rocky headwaters and downslope soil‐mantled slopes, a negative correlation is found between the hypsometric integral and catchment area, suggesting that the scale independency of the hypsometric integral occurs essentially in headwater rock basins. Geomorphometric indices (residual relief and surface roughness) have contributed to interpreting the variability of surface morphology, which is related to the geo‐structural complexity of the catchments.     

闲暇时间约束对中山陵景区国内客源市场空间结构的影响

闲暇时间是旅游需求得以实现的必要条件之一,居民闲暇时间的变化必然对旅游地客源市场空间结构产生影响。选择"五一"小长假、"十一"黄金周及暑假3类6个不同闲暇时长的时段,基于现场问卷调研,使用客源地地理集中指数、客源吸引半径、距离衰减曲线及引力模型研究闲暇时间约束对南京市中山陵景区客源市场空间结构的影响,发现随着假日时长的增加,居民出游距离受闲暇时间的约束降低,从而旅游地客源吸引半径增大,客源地集中指数降低、距离衰减曲线变缓、距离衰减指数降低。研究结果表明,在不同时长的闲暇时间约束下,距离因素对景区客流量的影响最大,其次为收入(客源地人均地区生产总值),而客源地人口规模因素的影响最小。     

Litho-tectonic and precipitation implications on landslides,Yamuna valley,NW Himalaya

ABSTRACT

An attempt is made to explain the relationship of landslides to litho-tectonic and precipitation regimes. The possible influence of these factors on the dimensional pattern of landslides is also inferred. The Yamuna River valley, NW Himalaya, which traverses the Higher Himalaya (HH) and Lesser Himalaya (LH) rock mass, endures disastrous landslides and hence is taken as the case for study. To achieve the objectives, proxies like stream length gradient, topographic profile, steepness index, and ratio of valley floor width to valley height were used to infer a spatially varying tectonic regime, whereas rainfall data and Normalized Difference Vegetation Index were used to determine spatial differences in precipitation and vegetation variability, respectively. Dimensional patterns of landslides utilized the landslide area and volume. The higher reaches of the HH and lowest part of the LH show rockfall dominance associated with relatively high tectonic activity, whereas most of the debris slides coincide with regional thrusts. Total area and volume occupied by the landslides are ~1.5 ± 0.16 × 10⁶ m² and ~4.7 ± 1.2 × 10⁶ m³, respectively. Dimensions of debris slides were found to be less influenced by the litho-tectonic and precipitation regimes, whereas the dimensions of rockfalls were found to be more sensitive to these conditions.     

Comment on ‘Concerning “The economic evaluation of implementing a GIS‘”

Abstract

A fragmentation index has been implemented as a region based GIS operator to describe the spatial distribution of thematic classes in one data layer within map regions defined in another data layer. It has been applied to integrated analysis of digital maps and classified remote sensing data, for estimation of landscape complexity within watersheds and for detection of logged forest stands. The properties of the fragmentation index, when applied in this manner, are discussed. The fragmentation index is suggested as a valuable means of describing image characteristics of spectrally heterogeneous map regions.     

SPATIAL SCALE INFLUENCES ON MODELED RUNOFF FOR LARGE WATERSHEDS

Modeling the runoff subsystem for large drainage basins requires simplification in representing natural processes owing to the spatial variability of mass and energy transfers in a watershed. Many models represent temporally and spatially distributed watershed variables by some form of aggregation or lumping. Scale becomes a factor in the lumping decision because some of the variables are spatially continuous while others are spatially discontinuous. The effects of scale differences on lumping in large watersheds is examined using the 27,300 km² drainage area of the Deschutes River, Oregon. The watershed is modeled using three different spatial aggregations for representing the runoff subsystem. Agreement between modeled and observed monthly runoff for water years 1951-60 is analyzed to evaluate the magnitude of the difference between corresponding observed and modeled values. Increasing the number of spatial units in the model from 1 to 9 reduces all of the error terms by about 35 percent, but 20 spatial units in the model reduce the error terms by 50 percent or more. These data provide explicit evidence of improved modeling accuracy achieved by employing a disaggregated watershed model to represent spatially heterogeneous conditions in a large drainage basin. [Key words: watershed modeling, scale, large watersheds, hydroclimate, Deschutes Basin.]     

FLOOD DISTURBANCE AND THE DISTRIBUTION OF RIPARIAN SPECIES DIVERSITY*

ABSTRACT. Biodiversity varies considerably in Southern Californian riparian vegetation. The intermediate disturbance hypothesis posits greatest diversity in settings that are subject to moderate-intensity disturbance. Flood intensity tends to vary systematically in watersheds, potentially imposing patterns of biodiversity. In two study watersheds, species richness increases with flood severity. Diversity, or heterogeneity, is less predictable: Biodiversity patterns in these watersheds are complicated by atypical patterns of flood severity. Although riparian diversity may be intimately dependent on flood disturbance, the relationship is predictable only with due attention to the physiographic details of individual stream networks.     

黄土高原典型小流域道路特征及影响因素

通过GPS野外实测黄土高原纸坊沟小流域的道路特征,在GIS空间分析等方法支持下研究了流域内各级道路的分布规律。研究表明:黄土高原道路可分为4级,2级以下的土路是小流域的代表路型。各级别道路总长度都随级别增大而增加且累计总长度与道路级别线性相关,道路平均长度和密度则随级别增大而减小。道路网系和流域水系在结构规律上具有一定的相似性。不同级别道路分布范围受地形特征影响不同。爬坡道路坡度与地表坡度之间存在线性回归关系,且次级道路分布受主路控制;典型爬坡路在大于25°坡度范围内多呈"之"字形弯曲,随坡度的减小道路弯曲跨度和与等高线夹角增大。研究结果有助于定量模拟黄土高原地区道路分布特征,并为土壤侵蚀模型中道路影响因子的确定提供参考。