Sediment delivery linkages in a chaparral watershed following a wildfire

The purpose of this research is to study the temporal and spatial sediment delivery to and within the stream network following a wildfire on a chaparral watershed in Arizona, USA. Methods include interpretation of channel processes (aggradation, degradation) from sequential aerial photographs, field measurements of sediment delivery, and overland flow from ten microwatersheds having different vegetation cover (no vegetation, chaparral cover, and bare with vegetation buffer strips). The response of the watershed to the fire was very complex. The fire reduced the chaparral cover to zero in most locations and severe erosion led to filling of the channels by sediment. With vegetation recovery, sediment delivery from the watershed practically ceased. Vegetation buffer strips were mainly responsible for arresting the sediment delivered from bare hillslopes. Relatively clear water, entering the channels, caused degradation in the tributaries that delivered the sediment into the main stream at El Oso Creek. Due to high water infiltration by immense volumes of sediment deposits in the middle reach, the sediment from the tributaries was deposited as in-channel fans. In contrast, the upper reach of El Oso Creek behaved similarly to the tributaries. It aggraded after the fire and was followed by degradation. The low reach of El Oso Creek is degrading because it is still adjusting base level to the incision of the master stream. Implications of this study are that land managers, concerned to avoid severe erosion and sedimentation following disturbance, should concentrate on the establishment and enhancement of vegetation buffer strips along channel banks.     

WATER QUALITY BENEATH URBAN RUNOFF WATER MANAGEMENT BASINS1

ABSTRACT: The chemical impact of urban runoff water on water quality beneath five retention/recharge basins was investigated as part of the US EPA's Nationwide Urban Runoff Program in Fresno, California. Soil water percolating through alluvium soils and the ground water at the top of the water table were sampled with ceramic/Teflon vacuum water extractors at depths up to 26 m during the two-year investigation. Inorganic and organic pollutants are present in the runoff water delivered to the basins. No significant contamination of percolating soil water or ground water underlying any of the five retention/recharge basins has occurred for constituents monitored in the study. The oldest basins was constructed in 1962. The concentration of selected trace elements in the ground water samples was similar to the levels reported in the regional ground water. None of the pesticides or other organic priority pollutants, for which water samples were analyzed, was s̊ detected except diazinon which was found in trace amounts (0.3 μg/L or less) in only three soil water samples. These results are important to the continued conservation of storm water and the development of a best management practice for storm-water management using retention/recharge basins in a semi-arid climate.     

WATER BALANCE OF PACIFIC ATOLLS1

ABSTRACT: This study presents an estimate of water balance components for Pacific atolls under average dimatological conditions. Figures show annual potential evapotranspiration, annual recharge for rain-fed and aquifer-fed vegetated areas, and the number of months that potential evapotranspiration exceeds actual evapotranspiration (indicating water stress) under average conditions. The method relies on the assumption that small islands have minimal influence on cloudiness and precipitation. The potential evapotranspiration is computed using the equilibrium evaporation concept, and estimates of monthly soil water storage and recharge follow Thornthwaite's bookkeeping method. Gradients in potential evapotranspiration run primarily north-south, though for the equatorial zone potential evapotranspiration declines from east to west, opposing the trend in rainfall. Recharge estimates range from 250 mm in the central Tuamotu Archipelago and zero in eastern Kiribati to over 2000 mm per year in the southern Caroline Islands (U.S. Trust Territory) and Solomon Islands. The sensitivity of the model to intra-month rainfall variability and a range of available soil moisture values is discussed.     

Pesticide and Transformation Product Detections and Age‐Dating Relations from Till and Sand Deposits1

Abstract:  Pesticide and transformation product concentrations and frequencies in ground water from areas of similar crop and pesticide applications may vary substantially with differing lithologies. Pesticide analysis data for atrazine, metolachlor, alachlor, acetochlor, and cyanazine and their pesticide transformation products were collected at 69 monitoring wells in Illinois and northern Indiana to document occurrence of pesticides and their transformation products in two agricultural areas of differing lithologies, till, and sand. The till is primarily tile drained and has preferential fractured flow, whereas the sand primarily has surface water drainage and primary porosity flow. Transformation products represent most of the agricultural pesticides in ground water regardless of aquifer material – till or sand. Transformation products were detected more frequently than parent pesticides in both the till and sand, with metolachlor ethane sulfonic acid being most frequently detected. Estimated ground‐water recharge dates for the sand were based on chlorofluorocarbon analyses. These age‐dating data indicate that ground water recharged prior to 1990 is more likely to have a detection of a pesticide or pesticide transformation product. Detections were twice as frequent in ground water recharged prior to 1990 (82%) than in ground water recharged on or after 1990 (33%). The highest concentrations of atrazine, alachlor, metolachlor, and their transformation products, also were detected in samples from ground water recharged prior to 1990. These age/pesticide detection relations are opposite of what would normally be expected, and may be the result of preferential flow and/or ground‐water mixing between aquifers and aquitards as evident by the detection of acetochlor transformation products in samples with estimated ground‐water ages predating initial pesticide application.     

Hydrologic Model Framework for Water Resources Planning in the Santa Cruz River,Southern Arizona1

Abstract: The authors develop a model framework that includes a set of hydrologic modules as a water resources management and planning tool for the upper Santa Cruz River near the Mexican border, Southern Arizona. The modules consist of: (1) stochastic generation of hourly precipitation scenarios that maintain the characteristics and variability of a 45‐year hourly precipitation record from a nearby rain gauge; (2) conceptual transformation of generated precipitation into daily streamflow using varied infiltration rates and estimates of the basin antecedent moisture conditions; and (3) surface‐water to ground‐water interaction for four downstream microbasins that accounts for alluvial ground‐water recharge, and ET and pumping losses. To maintain the large inter‐annual variability of streamflow as prevails in Southern Arizona, the model framework is constructed to produce three types of seasonal winter and summer categories of streamflow (i.e., wet, medium, or dry). Long‐term (i.e., 100 years) realizations (ensembles) are generated by the above described model framework that reflects two different regimes of inter annual variability. The first regime is that of the historic streamflow gauge record. The second regime is that of the tree ring reconstructed precipitation, which was derived for the study location. Generated flow ensembles for these two regimes are used to evaluate the risk that the regional four ground‐water microbasins decline below a preset storage threshold under different operational water utilization scenarios.     

地下水回灌补源防治咸水入侵技术研究 --以山东省广绕县为例

山东省广绕县井灌区由于长期超采地下水，引起区域地下水位持续下降、咸水入侵和地裂缝等一系列环境地质问题，成为区域社会和经济持续发展的制约因素。采用地下水回灌补源和调蓄技术是防治咸水入侵的有效途径。探讨了地下水回灌补源系列技术方法，涉及试验研究、数学模拟与优化技术等。室内、野外试验研究为地下水回灌规划和设计以及建立数值模拟模型提供了基本数据和参数。为了优化调整地下水开采量和回灌补源，建立了管理模型。管理模型预测表明，引用黄河水和汛期雨洪水回灌补源，以及通过节水减少漏斗区地下水开采量等系列措施可以有效地阻止咸水入侵，逐步改善区内的地下水环境。     

HYDROLOGIC IMPLICATIONS OF GREATER GROUND‐WATER RECHARGE TO LAS VEGAS VALLEY,NEVADA1

ABSTRACT: Published estimates of natural recharge in Las Vegas Valley range between 21,000 and 35,000 acre‐feet per year. This study examined the underlying assumptions of previous investigations and evaluated the altitude‐precipitation relationships. Period‐of‐record averages from high altitude precipitation gages established in the 1940s through the 1990s, were used to determine strong local altitude‐precipitation relationships that indicate new total precipitation and natural recharge amounts and a new spatial distribution of that recharge. This investigation calculated about 51,000 acre‐feet per year of natural recharge in the Las Vegas Hydrographic Basin, with an additional 6,000 acre‐feet per year from areas tributary to Las Vegas Valley, for a total of 57,000 acre‐feet per year. The total amount of natural recharge is greater than estimates from earlier investigations and is consistent with a companion study of natural discharge, which estimated 53,000 acre‐feet per year of outflow. The hydrologic implications of greater recharge in Las Vegas Valley infer a more accurate ground‐water budget and a better understanding of ground‐water recharge that will be represented in a ground‐water model. Thus model based ground‐water management scenarios will more realistically access impacts to the ground‐water system.     

再生水补充地下水水质指标及控制技术

再生水补充地下水是扩大污水回用最有益的一种方式,具有广阔发展前景.本文分析与总结了国内外再生水补充地下水研究与应用实例、水质标准,结合我国再生水的水质特点及水文地质状况,从保护地下水资源和人体健康的角度,探讨了我国利用再生水补充地下水应控制的水质指标及控制技术.按地表回灌和井灌方式分别提出了水质基本控制项目COD、BOD、氨氮、粪大肠菌群数等22项,选择控制项目Hg、三氯甲烷等重金属和微污染有机物52项及其建议指标值,并提出了再生水处理控制技术.     

百脉泉泉群泉水氢氧稳定同位素时空变化特征

研究泉水氢氧稳定同位素时空变化特征,探究泉水的补给来源,对水资源管理及旅游业可持续发展具有重要指导意义。以百脉泉泉群为研究区,通过分析降水及泉水中的氢氧稳定同位素特征,获取了本地大气降水线、泉水同位素时空变化特征及蒸发线,并探究了百脉泉泉水的补给来源。结果表明：大气降水中δ²H的波动范围为-151.55‰δ¹⁸O—-4.28‰,δ¹⁸O的波动范围为-19.93‰δ¹⁸O—-0.52‰,δ²H和δ¹⁸O在时间上的分布规律相似,均呈现双峰状(“M”型),本地大气降水线(LMWL)为：δ²H=7.58×δ¹⁸O+4.17。百脉泉泉水的δ²H的波动范围为-65.23‰δ¹⁸O—-37.01‰,δ¹⁸O的波动范围为-8.99‰δ¹⁸O—-4.04‰。泉水δ²H—δ¹⁸O均落在本地大气降水线上或...     

降水入渗补给地下水过程分析

该文总结了降水入渗补给的模式,通过分析活塞式降水入渗、降水入渗补给的滞后和延迟、降水入渗优先补给等,研究了土壤不同岩性、不同埋深、不同降水时段与不同土壤含水量条件下的降水入渗补给过程．图5,表1,参8．