GEOMORPHIC PARAMETERS PREDICT HYDROGRAPH CHARACTERISTICS IN THE SOUTHWEST1

ABSTRACT: Critical design characteristics of ephermal runoff such as hydrograph rise time, duration, mean peak discharge, volume, peak-volume ratio, and maximum flood were related to physical basin parameters such as area, shape, slope, drainage density, basin relief, stream length, and combinations of these in intermontane watersheds representative of the Mexican Highland section of the Basin and Range Province. Parameters used were restricted to those easily obtainable from maps or aerial photographs. A parameter expressing basin shape and size was developed which proved to be as accurate a predictor as others used in existing prediction equations tested and was simpler and faster to derive. Simple prediction equations derived for hydrograph characteristics were all significant except for volume at the 5% level; three were significant at the 1% level. Relationships determined are applicable in semi-arid basins of the Southwest up to 60 square miles (155 km²) in area.     

FOG DRIP IN THE BULL RUN MUNICIPAL WATERSHED,OREGON1

ABSTRACT: Net precipitation under old growth Douglas fir forest in the Bull Run Municipal Watershed (Portland, Oregon) totaled 1739 mm during a 4Cbweek period, 387 mm more than in adjacent clearcut areas. Expressing data on a full water year basis and adjusting gross precipitation for losses due to rainfall interception suggest fog drip could have added 882 mm (35 in) of water to total precipitation during a year when precipitation measured 2160 mm in a rain gage in a nearby clearing. Standard rain gages installed in open areas where fog is common may be collecting up to 30 percent less precipitation than would be collected in the forest. Long term forest management (Le., timber harvest) in the watershed could reduce annual water yield and, more importantly, summer stream flow by reducing fog drip.     

EFFECTS OF URBANIZATION ON BASE FLOW OF SELECTED SOUTH-SHORE STREAMS,LONG ISLAND,NEW YORK1

ABSTRACT: Hydrograph analysis of six streams on the south shore of Long Island indicates that eastward urbanization during the last three decades has significantly reduced base flow to streams. Before urbanization, roughly 95 percent of total annual stream flow on Long Island was base flow. In urbanized southwestern Nassau County, storm water sewerage, increased impervious surface area, and sanitary sewerage have reduced base flow to 20 percent of total stream flow. In an adjacent urbanized but unsewered area in southeastern Nassau County, base flow has decreased to 84 percent of total annual stream flow. In contrast, base flow in two streams in rural areas has remained virtually constant, averaging roughly 95 percent of total annual flow throughout the 1955-70 study period. Double-mass curve analysis of base flow as a percentage of total annual stream flow indicates that (1) changes in stream flow characteristics began in the early 1960's in the sewered area and in the late 1960's in the later urbanized, unsewered area, and (2) a new equilibrium has been established between the streams in the sewered area and the new hydrologic characteristics of their urbanized drainage basins.     

超高速瞬态测试系统软硬件构架设计研究

目的研究采样频率为2~10 MHz的64通道超高速同步瞬态测试系统的设计技术,实现两类典型超高速瞬态测试系统的硬件架构设计与软件架构设计。方法一类采用PXI-Express高带宽总线和高速RAID磁盘阵列架构构建持续流盘存储的连续高速测试系统,另一类是采用大容量板载数据缓存和PXI总线事后下载传输数据的架构构造高速测试系统。在高性能测试软件设计方面,主要应用生产者/消费者结构与有限状态机相结合的软件架构进行高性能测试系统软件设计。结果目前64通道下基于持续流盘架构的测试系统受数据记录的速度限制系统最高采样频率仅达2.5 MHz,而基于板载缓存数据与PXI总线事后下载数据架构的测试系统最高采样频率可达10 MHz,测试时长可达5 s。结论当前两类架构的测试系统均可满足超高速瞬态测试需求,设计时需根据需求的最高采样频率决定使用的架构形式。     

Creating False Images: Stream Restoration in an Urban Setting

Stream restoration has become a multibillion dollar business with mixed results as to its efficacy. This case study utilizes pre‐ and post‐monitoring data from restoration projects on an urban stream to assess how well stream conditions, publicly stated project goals, and project implementation align. Our research confirms previous studies showing little communication among academic researchers and restoration practitioners as well as provides further evidence that restoration efforts tend to focus on small‐scale, specific sites without considering broader land use patterns. This study advances our understanding of restoration by documenting that although improving ecological conditions is a stated goal for restoration projects, the implemented measures are not always focused on those issues that are the most ecologically salient. What these projects have accomplished is to protect the built environment and promote positive public perception. We argue that these disconnects among publicized goals for restoration, the implemented features, and actual stream conditions may create a false image of what an ecologically stable stream looks like and therefore perpetuate a false sense of optimism about the feasibility of restoring urban streams.     

Dissolved organic sulfur in streams draining forested catchments in southern China

Dissolved organic sulfur (DOS) is an important fraction for sulfur mobilization in ecosystem. In this work stream waters were sampled in 25 forested sites in southern China to study the dissolved sulfur fractions. Dissolved sulfur was fractionated into dissolved organic sulfur (DOS) and inorganic sulfate (SO₄^2-) for 95 stream water samples. The results showed that the concentration of DOS ranged from 0 to 13.1 mg/L (average 1.3 mg/L) in all the streams. High concentrations of DOS in stream waters were found in the sites with high concentrations of sulfate. DOS constituted less than 60.1% of dissolved sulfur (average 17.9%). Statistical analysis showed that DOS concentration was correlated with SO₄^2- in streams waters and total sulfur in surface layer soils. The results also showed that DOS concentration in stream waters had a seasonal variation, but no trends were found with it. The implication was that the long term sulfur deposition had led the increase of the concentration and fraction of DOS in stream waters in acid rain prevailing regions     

长江上游典型农业源溪流溶存氧化亚氮(N2O)浓度特征及影响因素

随着农业非点源氮（N）污染的加剧,农田周边溪流成为重要的活性N汇和潜在的氧化亚氮（N₂O）排放源.为查明长江上游农业源溪流中溶存N₂O浓度的全年动态变化特征,于2014年12月~2015年10月开展紫色土丘陵区典型农田源头溪流N₂O浓度的连续采样观测,采用水-气顶空平衡-气相色谱法测定顶空气体中N₂O浓度,根据相关参数计算出本研究水体中的溶存N₂O浓度,并同步测定溪流水体物理化学指标,分析水中溶存N₂O浓度的主要影响因素.结果表明,长江上游紫色土丘陵区的典型农业源溪流的硝态氮（NO₃^--N）是最主要的活性N赋存形态（年均1.45 mg·L^-1）,溪流水体溶存N₂O质量浓度（以N计）全年平均为0.57 μg·L^-1（范围0.26~1.28 μg·L^-1）,冬、春、夏和秋季的均值分别为0.63、0.45、0.53和0.64 μg·L^-1,但季节间无显著差异.溪流水体溶存N₂O浓度全年都处于过度饱和状态（饱和度年平均为203.9%,范围109.7%~546.5%）,可见,农业源溪流全年均为潜在的N₂O释放源.溪流溶存N₂O浓度的变化主要由水体NO₃^--N浓度决定,N₂O的主要产生机制为反硝化作用;溪流季节平均N₂O饱和度在夏、秋季显著高于冬、春季,水中溶存N₂O饱和度的变化主要受水温和NO₃^--N浓度的共同影响.研究还发现农业源溪流中溶存N₂O浓度在4~10月（湿润季节）间波动明显,较强降雨可促使其水中NO₃^--N浓度在雨后短期内升高,进而促进水体反硝化作用,导致雨后溪流中溶存N₂O浓度的增加.     

STREAM DEPLETION BY WELLS IN THE SOUTH PLATTE BASIN-COLORADO1

The agricultural production from the Lower South Platte Basin in Colorado represents a significant portion of the state economy. Until the early 1950's the production had developed almost exclusively by use of river water. Drought conditions combined with improved well technology resulted in an inordinate amount of well development in the valley during the period 1952-56. These wells were used for supplemental supply in many cases, but the application of sprinkler irrigation brought many acres of here-to-fore dry land into irrigated production. As a result of the vast amounts of groundwater withdrawal by the newly developed wells, senior surface appropriators found a decreasing amount of water available for use in the streams. The legislature, observing the doctrine of prior appropriation, ruled that all surface and ground water in a tributary would be treated and administered as one resource. This, of course, spelled doom for the well-oriented segment of the economy. Analysis of a segment of the river on an inflow-outflow basis was made with careful determination of all inflow-outflow in the study reach to include correlations required to determine ungaged side-channel in-flow and unmetered irrigation wells. Results indicate that wells have intercepted normal return flows to the river resulting in a decreased amount of surface water during the irrigation season. Stream depletion appears to equal the expected consumptive use of well water which ranged between 40% to 50% of the groundwater extraction.     

A stochastic-advective transport model for NAPL dissolution and degradation in non-uniform flows in porous media

Remediation schemes for contaminated sites are often evaluated to assess their potential for source zone reduction of mass, or treatment of the contaminant between the source and a control plane (CP) to achieve regulatory limits. In this study, we utilize a stochastic stream tube model to explain the behavior of breakthrough curves (BTCs) across a CP. At the local scale, mass dissolution at the source is combined with an advection model with first-order decay for the dissolved plume. Field-scale averaging is then employed to account for spatial variation in mass within the source zone, and variation in the velocity field. Under the assumption of instantaneous mass transfer from the source to the moving liquid, semi-analytical expressions for the BTC and temporal moments are developed, followed by derivation of expressions for effective velocity, dispersion, and degradation coefficients using the method of moments. It is found that degradation strongly influences the behavior of moments and the effective parameters. While increased heterogeneity in the velocity field results in increased dispersion, degradation causes the center of mass of the plume to shift to earlier times, and reduces the dispersion of the BTC by lowering the concentrations in the tail. Modified definitions of effective parameters are presented for degrading solutes to account for the normalization constant (zeroth moment) that keeps changing with time or distance to the CP. It is shown that anomalous dispersion can result for high degradation rates combined with wide variation in velocity fluctuations. Implications of model results on estimating cleanup times and fulfillment of regulatory limits are discussed. Relating mass removal at the source to flux reductions past a control plane is confounded by many factors. Increased heterogeneity in velocity fields causes mass fluxes past a control plane to persist, however, aggressive remediation between the source and CP can reduce these fluxes.