Application of a 2D hydrodynamic model to design of reach‐scale spawning gravel replenishment on the Mokelumne River,California

In‐stream chinook salmon (Oncorhynchus tschawytscha) spawning habitat in California's Central Valley has been degraded by minimal gravel recruitment due to river impoundment and historic gravel extraction. In a recent project marking a new direction for spawning habitat rehabilitation, 2450 m³ of gravel and several boulders were used to craft bars and chutes. To improve the design of future projects, a test was carried out in which a commercial modelling package was used to design and evaluate alternative gravel configurations in relation to the actual pre‐ and post‐project configurations. Tested scenarios included alternate bars, central braid, a combination of alternate bars and a braid, and a flat riffle with uniformly spaced boulders. All runs were compared for their spawning habitat value and for susceptibility to erosion. The flat riffle scenario produced the most total, high, and medium quality habitat, but would yield little habitat under flows deviating from the design discharge. Bar and braid scenarios were highly gravel efficient, with nearly 1 m² of habitat per 1 m³ of gravel added, and yielded large contiguous high quality habitat patches that were superior to the actual design. At near bankfull flow, negligible sediment entrainment was predicted for any scenario. Copyright © 2004 John Wiley & Sons, Ltd.     

长江源区1980-2010年土地利用变化及影响分析研究

长江源区地处我国三江源自然保护区内,作为长江的源头是整个长江开发利用和环境保护的关键一环。从源区土地利用/覆盖角度分析源区自然环境状态变化,利用ENVI和Arc GIS软件对1980-2010年4期长江源区遥感数据进行解译,以土地利用动态度、综合程度指数及转移矩阵作为评价指标。结果表明:长江源区地貌类型以草地和裸地为主,建筑用地和耕地最少;全时段1980-2010年间,水域面积减少最多,裸地面积增加最多,相对于初期而言源区自然环境有所下降; 1990-2000年间是土地利用开发强度最强的时段,随着2000年三江源保护区的建立,2000-2010年长江源区土地利用朝着恢复方向发展,自然环境有所改善。     

长江源通天河段辫状河道形态特征与变化规律

长江源广泛发育辫状河道,共同组成一个庞大的辫状河群,在水流泥沙与河床地形数据缺乏的条件下,长江源辫状河道形态的时空变化尚缺少研究。基于Landsat遥感影像解译,研究长江源通天河局部辫状河段的平面形态特征与分汊强度的时空变化规律。结果表明:1987—2016年辫状河段的水域面积与河床面积之比在年内呈现单峰变化过程,即汛期4—9月份逐渐变大,非汛期10月—次年3月趋于变小至基本不变,而且近30 a有所增加,间接反映了长江源径流量增加的趋势。辫状河段的36个横断面的汊道数指数和汊道长度指数分别为4~10和5~12,在1994,2005,2015年其均值几乎维持不变,表明此辫状河段的整体形态具有自相似性且河型不变。     

融合光谱和几何特征的高分辨率遥感变化检测研究

针对高分辨率遥感影像城市区域地类复杂的特点,提出了一种融合光谱和几何特征的多时相高分辨率遥感变化检测方法。在获取光谱和几何差异影像的基础上,采用模糊分类的方法,进行变化类和非变化类区分,建立各类的隶属度图像。采取基于模糊集理论的融合算法,对各种检测方法获取的隶属度图像进行有效融合,以减小部分区域的模糊度,提高变化类和非变化类的检测精度。采用城区多时相高分辨率影像为实验数据,进行各种变化检测方法的对比与分析,实验结果表明,融合光谱和几何特征的方法所获取的检测结果与光谱、几何差异影像法相比,具有检测精度高、漏检率低的特点。     

Multi‐scale modelling of land‐use change and river training effects on floods in the Rhine basin

Land‐use changes effects on floods are investigated by a multi‐scale modelling study, where runoff generation in catchments of different sizes, different land uses and morphological characteristics are simulated in a nested manner. The macro‐scale covers the Rhine basin (excluding the alpine part), the upper meso‐scale covers various tributaries of the Rhine and three lower meso‐scale study areas (100–500 km²) represent different characteristic land‐use patterns. The main innovation is the combination of models at different scales and at different levels of process representation in order to account for the complexity of land‐use change impacts for a large river basin. The results showed that the influence of land‐use on storm runoff generation is stronger for convective storm events with high precipitation intensities than for long advective storms with low intensities. The simulated flood increase at the lower meso‐scale for a scenario of rather strong urbanization is in the order of 0 and 4% for advective rainfall events, and 10–30% for convective rain storms with a return period of 2–10 years. Convective storm events, however, are of hardly any relevance for the formation of floods in the large river basins of Central Europe, because the extent of convective rainstorms is restricted to local occurrence. Due to the dominance of advective precipitation for macro‐scale flooding, limited water retention capacity of antecedent wet soils and superposition of flood waves from different tributaries, the land‐use change effects at the macro‐scale are even smaller, for example at Cologne (catchment area 100 000 km²), land‐use change effects may result in not more than 1–5 cm water level of the Rhine. Water retention measures in polders along the Upper and Lower Rhine yield flood peak attenuation along the Rhine all the way down to the Dutch border between 1 and 15 cm. Copyright © 2007 John Wiley & Sons, Ltd.     

基于GF-2影像的大运河及河长制治理成效评价

基于遥感技术提出利用植被绿化面积、水体面积和景观格局等因素的时空变化对比评价方法,通过对高分遥感影像数据校正、融合、镶嵌和解译,计算植被指数、水体指数和景观格局指数变化,客观反映生态环境保护修复的时空变化情况,并且成本低,时效性强。基于大运河核心监控区北京段的试验表明:研究区内2015—2017年植被绿化面积减少,水体面积增加;2017—2019年植被绿化面积骤增,水体面积增加。从总体上看,植被绿化面积和水体面积均呈扩张趋势,景观格局趋于均匀化、规则化。在一定程度上体现了河长制推行下,大运河治理颇有成效,依此作为督察评估河长工作成效的数据支撑和依据,可量化,更具有客观性,是一种可行的方法。     

The calculation of riverine ecological instream flows and runoff profit‐loss analysis in a coal mining area of northern China

The northern Shaanxi province of China has severe water shortages, especially in coal mining areas, and it is very important to calculate the riverine ecological instream flows (EIFs) and analyse the runoff profit‐loss situation. Using the Kuye River as a case study, the EIF was calculated for different years and seasons using the instream flows rate (IFR) method and compared with the Tennant and the minimum monthly average flow (MAF) methods. The recommended value of the Kuye River EIF was obtained by an analysis of the results of these three methods. The river runoff profit‐loss situation associated with the EIF was also calculated and the main reason for the loss explained. The Kuye River EIF was calculated to be 1.69 to 11.14 m³/s by the IFR method, 1.94 to 8.50 m³/s by the Tennant method, and 3.81 to 10.87 m³/s by the MAF method. Based on these results, the EIF annual recommended value of the Kuye River was 4.00 m³/s for the 1961–2010 period. The wet season (July–October), average season (March–June), and dry season (November–following Feb) EIFs were 6.50, 3.50, and 2.00 m³/s, respectively. The Kuye River had a large surplus runoff within the EIF prior to1999, but from 1999 to 2010, the runoff and EIF were very close and the April to June average runoff did not meet the EIF. The main factors that affected the river runoff were rainfall, temperature, water and soil conservation, coal mining, and water consumption for industry and domestic use, with coal mining becoming a more important factor since 1999. This case study provides important technical support and guidance for the ecological restoration of the Kuye River basin, and the concept can be applied to other similar coal mining areas.     

Large dam removal and early spontaneous riparian vegetation recruitment on alluvium in a former reservoir: Lessons learned from the pre‐removal phase of the Sélune River project (France)

The restoration of ecological continuity along the Sélune River (Normandy, France) involves the removal of two tall hydroelectric dams (36 m removed in 2019 and 16 m in 2021), a project without precedent in Europe. During the pre‐removal phase (2014–2018), we performed scientific monitoring of the vegetation that was colonizing alluvium in the former dam reservoir (length: 19 km; surface area: 151 ha). Our study aimed to analyse if spontaneous vegetation could ecologically restore the riparian zone and help maintain fine sediment after dam removal. We used colonization indicators related to vegetation structure, taxonomic richness and diversity, and composition. These indicators were calculated at two spatial scales (local, at a single site, and broad, along the reservoir). The aim was to (a) characterize the spontaneously established species pool; (b) analyse longitudinal patterns in vegetation colonization; and (c) assess temporal changes in the species community. Our results show that diverse plant communities have developed. Slight differences in longitudinal and lateral patterns existed; they were linked with habitat heterogeneity and the reservoir's slow pace of draining. We observed fast spontaneous terrestrialization, which has resulted in cover stabilization, decreased diversity, and the development of herbaceous riverbank communities, with very few invasive species. This finding suggests stabilization potential is high and passive ecological restoration could occur, at least locally. Further analyses focusing on functional traits could help inform future management decisions regarding revegetation on reservoir alluvium.