Individual Rainfall Research Articles

Evaluation of 2B31 TRMM‐product rain estimates for single precipitation events over a region with complex topographic features

An evaluation of precipitation estimations on the ground for individual rainfall events was carried out by comparing the 2B31 Tropical Rainfall Measuring Mission (TRMM) product versus a high‐density, rain gauge network deployed at the ground over a small (about 1000 km2) study area in a continental region characterized by complex topography and high altitude. This comparison, using categorical analysis, showed a good agreement for several skill parameters most frequently used in works of this type. In this paper, it is concluded that Odds Ratio Skill Score (ORSS) is a more reliable measure of skill for categorical statistics than other scores because it better reflects the agreement between the two data sets. Furthermore, ORSS allows one to test the significance of the results so it is possible to discriminate whether the resulting skill is due to pure chance (ORSS was significant in 70% of the cases studied). Although variance and mean analyses generally showed differences between data sets for both the amount and the distribution of rainfall rate over the study area, least squares fits indicate a very high and quite linear correlation for both the mean rainfall rate (r2 = 0.90) and the maximum amount of precipitation at a given point (r2 = 0.74). It is concluded that 2B31 TRMM data can be used in weather applications for the area studied here and others with complex orographical characteristics and also as a tool in the diagnosis of individual rain events in other regions where there are no other data sources available.

Characteristics of surface runoff in a sandy area in southern Mu Us sandy land

To better understand the key role of biological soil crusts (BSCs) in redistribution processes of limited water resources in semi-arid sandy ecosystems, surface runoff over BSCs in a sandy area in the southern Mu Us sandy area was observed in this study. The results indicated that runoff occurred twice among six rainfall events during the experimental period. Runoff yields varied among types of BSCs, and that they increased in the following order: light algae crusts, dark algae crusts and moss crusts. These findings showed that runoff yields were increasing with the development of BSCs. The percentage of runoff in individual rainfall events increased from light algae crusts to moss crusts, which indicated that the redistribution ratios of different types of BSCs differed. Surface runoff of BSCs may be influenced by rainfall, rain intensity, degree of water saturation of the BSCs before the rain and degree of development of BSCs. Formation of BSCs on the surface of sand dunes changed the spatial distribution pattern of water in this semi-arid sandy ecosystem, which increased the heterogeneity of resources such as water and nutrients. Therefore, making appropriate disturbances of BSCs during storm season is beneficial to maintaining the balance of natural resources in the semi-arid sandy ecosystem.

Determination of the removal efficiency of a vortex-type facility as a best management practice using the dynamic event mean concentration: a case study of a bridge in Yong-In city in Korea

Thus far, the removal efficiency of non-point-pollution source removal facilities has been evaluated for individual rainfall events. However, as the removal efficiency for part of a single rainfall event has not been evaluated, adapting the removal facilities for these concentrations is imprecise. Of 18 rainfall events, the removal efficiency of a vortex-type facility as a BMP (Best Management Practice), a non-point-pollution source removal method, was assessed in this study in four assessment techniques and analyzed. In addition, the efficiency was assessed for the concentration using dynamic EMC (Event Mean Concentration). At a higher concentration, the efficiency becomes higher in terms of the TSS, COD, and TP results. In the case of TP, the concentration range of 0~2 mg/L showed the highest efficiency. In the case of Zn, low efficiency was shown in a concentration range of 0.2∼0.6 mg/L.

Characteristics of local groundwater recharge cycles in South African semi-arid hard rock terrains – rainwater input

Rainfall events in semi-arid regions of South Africa are characteristically erratic in terms of depths and recurrence rates. Chemical assessment of cyclic rainwater has recognised 3 intervals, spaced over the hydrological cycle, reporting diverse hydrochemical compositions of rainwater in winter and summer rainfall regions. Winter rainwater is generated over the south Atlantic maritime waters. This rainwater contains noticeably higher concentrations of oceanic aerosols (NaCl) than the summer rainwater generated in the Intertropical Convergence Zone/equatorial western Indian Ocean. Sporadic addition of terrigenous dust generated over the continent substantially elevates concentrations of non-oceanic nitrogenous and sulphurous aerosols in the summer rainwater. Prominent seasonal variations in the rainwater hydrochemistry signature coincide with cyclic rainfall depths, characteristic of the semi-arid climate. Macro-element concentrations during the summer dry period, April to September, are relatively high in relation to those recorded for the wet cycle, October to March. However, the latter period reports a noticeably depleted hydrochemical rainwater input into the local groundwater budget during the peak rainfall period (January to March). The October-December (early) period represents a phase between a dusty, dry winter atmosphere and a relatively flushed atmosphere in December, after the first regional rainfall manifests around middle September. Individual early rainfalls contain even higher hydrochemical concentrations than the previous dry period, which subsequently diffuses as the airborne moisture content increases towards the peak rainfall period starting in January. Continuous rainfall event monitoring in the summer semi-arid regions identified short-term wet cycles contain ing extraordinary high rainfall events, referred to as episodic events. These wet cycles are highly erratic in time and may last from 3 to 8 consecutive days with a recurrence rate of 1 in 5 years. The rainwater hydrochemistry signature differs significantly from the normal rainfall composition and represents a unique opportunity for tracing the infiltrating rain water. For example, chloride concentrations from individual, high rainfall events (40 to 150 mm) may be as low as 0.4 mg·l-1, whereas the background value varies around 0.8 mg·l -1 . Environmental chloride represents a conservative tracer for estimating the migration between rainwater and groundwater recharge. The concentration levels are not constant throughout the year and may lead to erroneous assumptions when performing groundwater recharge estimations using accumulated rainwater samples and uncontrolled groundwater sampling techniques.

Scale‐invariant rainstorm hazard modelling for slopeland warning

AbstractPeriods characterized by heavy rain and storms can trigger Multiple Damaging Hydrological Events (MDHE), in turn developing flooding, erosion, downpours and other phenomena affecting human habitats and ecosystems. However, approaches and applications to model MDHE and weather warning under specific environmental conditions are still poor. Based on the interpretation of the rainstorm—MDHE relationship, it was reconsidered and extended to a model‐based rainstorms hazard index (RHI) developed in a previous paper, where rainstorm‐pulsing force and resistance state are combined. In this way, landscape response was achieved by individual formative rainfall events, while the specific sequence of events that can affect landscape was only assessed in a qualitative way. A retrospective evaluation of rainstorm hazard modelling, control runs, are also given for different precipitation durations (from 1 to 240 h), to be compared with MDHE at two test‐sites of Southern Italy (Benevento, Campania region; Scilla, Calabria region). For these sites, the complete series of historical MDHE which occurred during a 10 year period (1997–2008) was gathered and used to validate the results of the rainfall model. The tool is relatively simple and potentially attractive to rapidly prediction of adverse consequences of rainstorms. Perspectives for real‐time applications in emergency planning are ultimately given for an agenda in future research. Copyright © 2011 Royal Meteorological Society

Water table dynamics in undisturbed, drained and restored blanket peat

► We study a drained, restored (6 years prior to monitoring) and intact blanket peatland. ► Water tables are more variable in the order drained > restored > intact. ► Water table dynamics in the restored site were intermediate between drained and intact. ► Water table response is highly dependent on topographic location around drains. ► Recovery from drainage is slow. Peatland water table depth is an important control on runoff production, plant growth and carbon cycling. Many peatlands have been drained but are now subject to activities that might lead to their restoration including the damming of artificial drains. This paper investigates water table dynamics on intact, drained and restored peatland slopes in a blanket peat in northern England using transects of automated water table recorders. Long-term (18 month), seasonal and short-term (storm event) records are explored. The restored site had drains blocked 6 years prior to monitoring commencing. The spatially-weighted mean water table depths over an 18 month period were −5.8 cm, −8.9 cm and −11.5 cm at the intact, restored and drained sites respectively. Most components of water table behaviour at the restored site, including depth exceedance probability curves, seasonality of water table variability, and water table responses to individual rainfall events were intermediate between that of the drained and intact sites. Responses also depended on location with respect to the drains. The results show that restoration of drained blanket peat is difficult and the water table dynamics may not function in the same way as those in undisturbed blanket peat even many years after management intervention. Further measurement of hydrological processes and water table responses to peatland restoration are required to inform land managers of the hydrological success of those projects.

Desert shrub stemflow and its significance in soil moisture replenishment

Abstract. Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system influencing water utilization of plant roots at the stand scale, especially in water scarce desert ecosystems. In this study, stemflow of Caragana korshinskii was quantified by an aluminum foil collar collection method on re-vegetated sand dunes of the Shapotou restored desert ecosystem in northwestern China. Time domain reflectometry probes were inserted horizontally at 20 different soil profile depths under the C. korshinskii shrub to monitor soil moisture variation at hourly intervals. Results indicated that 2.2 mm precipitation was necessary for the generation of stemflow for C. korshinskii. Stemflow averaged 8% of the gross precipitation and the average funnelling ratio was as high as 90. The soil moisture in the uppermost soil profile was strongly correlated with individual rainfall and the stemflow strengthened this relationship. Therefore, it is favourable for the infiltrated water redistribution in the deeper soil profile of the root zone. Consequently, stemflow contributes significantly to a positive soil moisture balance in the root zone and the replenishment of soil moisture at deeper soil layers. This plays an important role in plant survival and the general ecology of arid desert environments.

Evaluation of catchment contributing areas and storm runoff in flat terrain subject to urbanisation

Abstract. Contributing Catchment Area Analysis (CCAA) is a spatial analysis technique developed and used for estimation of the hydrological connectivity of relatively flat catchments. It allows accounting for the effect of relief depressions on the catchment rainfall-runoff relationship which is not commonly considered in hydrological modelling. Analysis of distributed runoff was based on USDA runoff curves numbers (USDA, 1986), which utilised the spatial information on land cover and soil types, while CCAA was further developed to define catchment area contributing to river discharge under individual rainfall events. The method was applied to the Southern River catchment, Western Australia, showing that contributing catchment area varied from less than 20% to more than 60% of total catchment area under different rainfall and soil moisture conditions. Such variability was attributed to a compensating effect of relief depressions. CCAA was further applied to analyse the impact of urbanisation on the catchment rainfall-runoff relationship. It was demonstrated that in addition to an increase in runoff coefficient, urbanisation leads to expansion in the catchment area contributing to the river flow. This effect was more evident for the most frequent rainfall events, when an increase in contributing area was responsible for a 30–100% rise in predicted catchment runoff.

Calibration and validation of the Modified Universal Soil Loss Equation for estimating sediment yield on sloping plots: A case study in Khun Satan catchment of Northern Thailand

In this study, model testing, calibration, and validation of the Modified Universal Soil Loss Equation (MUSLE) model were carried out in Khun Satan catchment, Thailand, for the estimation of sediment yield in plots of different slopes using the S factor from the classic Universal Soil Loss Equation (USLE) and the McCool model, as the calibration parameter. In situ experimental plots were established with five different inclinations (9, 16, 25, 30, and 35%), with the other model parameters (e.g., erodibility, conservation practice, etc) being treated as constants. Sediment yields were recorded from 27 rainfall events between July and October 2003. It was found that both the classic USLE and the McCool models over-estimated sediment yields at all slope angles. However, the classic USLE produced a smaller relative error (RE) than the McCool model at plots with slopes of 9 and 16%, while the McCool model performed better at plots with slopes over 16% inclination. The calibration of the model using the S factor was then made for two slope range intervals, and the slope algorithm was later modified. The calibrated S factors were used in the prototype model for slope ranges of 9 to 16% using classic USLE and for slopes from 16 to 35% using the McCool model. The results revealed that an acceptable accuracy can be obtained through model calibration. The model validation based on paired t-test, on the other hand, showed that there was no difference (α = 0.05) between measured and estimated sediment yield using both models. This result indicates that if data on various slope gradients are limited, MUSLE needs to be calibrated before application, especially with respect to topographic factors, in order to obtain an accurate estimate of the sediment yield from individual rainfall events.

Short-time measurements of interception in mountain spruce forest

Short-time measurements of interception in mountain spruce forestOpen area rainfall and throughfall measurements in the Western Tatra Mountains (altitude about 1500 m a.s.l.) made by tipping bucket gauges were used to estimate the usefulness of the short-time data in analysis of spruce interception. The 10-minute data from period 13 May-13 October 2009 did not reveal meaningful correlations between the open area rainfall and throughfall. Aggregated measurements representing individual rainfall events were more useful. They showed linear relationship between open area rainfall and throughfall for events with total rainfall depth in the open area exceeding 5 mm. Correlation between open area rainfall and throughfall for rainfall events with duration above 120 minutes was significantly better than for the shorter ones. Mean values of interception (percentage of open area rainfall which did not appear in throughfall) of individual rainfall events was high. When we excluded events for which throughfall was higher than the open area rainfall, mean interception for larger and longer rainfall events was 46% and 48%, respectively. For smaller (runoff depth below 5 mm) and shorter events (duration below 2 hours) the mean interception was 70% and 72%, respectively. However, the data revealed very high variability of interception.

Contrasting physiological responsiveness of establishing trees and a C4 grass to rainfall events, intensified summer drought, and warming in oak savanna

AbstractClimate warming and drought may alter tree establishment in savannas through differential responses of tree seedlings and grass to intermittent rainfall events. We investigated leaf gas exchange responses of dominant post oak savanna tree (Quercus stellata and Juniperus virginiana) and grass (Schizachyrium scoparium, C4 grass) species to summer rainfall events under an ambient and intensified summer drought scenario in factorial combination with warming (ambient, +1.5 °C) in both monoculture and tree‐grass mixtures. The three species differed in drought resistance and response of leaf gas exchange to rainfall events throughout the summer. S. scoparium experienced the greatest decrease in Aarea (−56% and −66% under normal and intensified drought, respectively) over the summer, followed by Q. stellata (−44%, −64%), while J. virginiana showed increased Aarea under normal drought (+13%) and a small decrease in Aarea when exposed to intensified summer drought (−10%). Following individual rainfall events, mean increases in Aarea were 90% for S. scoparium, 26% for J. virginiana and 22% for Q. stellata. The responsiveness of Aarea of S. scoparium to rainfall events initially increased with the onset of drought, but decreased dramatically as summer drought progressed. For Q. stellata, Aarea recovery decreased as drought progressed and with warming. In contrast, J. virginiana showed minimal fluctuations in Aarea following rainfall events, in spite of declining water potential, and warming enhanced recovery. J. virginiana will likely gain an advantage over Q. stellata during establishment under future climatic scenarios. Additionally, the competitive advantage of C4 grasses may be reduced relative to trees, because grasses will likely exist below a critical water stress threshold more often in a warmer, drier climate. Recognition of unique species responses to critical global change drivers in the presence of competition will improve predictions of grass–tree interactions and tree establishment in savannas in response to climate change.

Short communication: Effect of altitude on erosive characteristics of concurrent rainfall events in the KwaZulu-Natal Drakensberg

High-resolution rainfall data from two stations in the northern KwaZulu-Natal Drakensberg provide insight into the effect of altitude on individual rainfall event characteristics. The effect of altitude on the duration and erosivity (rainfall intensity and kinetic energy) of concurrent rainfall on the escarpment and in the foothills is analysed using 5-min interval data for the calendar year 2003. A cumulative total of 229 rainfall events, measured at the Royal Natal National Park station (1 392 m a.m.s.l.) and a temporary station on the escarpment at Sentinel Peak (3 165 m a.m.s.l.), were considered, of which 79 rainfall events were found to fall concurrently at the two stations. The data indicate that the concurrent events generate rainfall for longer on the escarpment, but that the amount of rain produced as well as the intensity at which it falls is less than that in the foothills, both in summer and winter. The escarpment appears to limit erosivity, with only 11 events meeting the set criteria for erosivity in the foothills but failing to meet the same criteria on the escarpment. This decrease in erosivity contrasts with previous models for the Drakensberg that demonstrate higher erosivity in the upper reaches, but concurs with studies in mountainous regions elsewhere which found that erosivity decreases with altitude. It is tentatively suggested that the difference in rainfall characteristics could be related to the sources of precipitation and the manner in which the escarpment zone affects the formation and distribution of rainfall. The paper also highlights the need for further research into the association between rainfall structure and synoptic conditions and the effect that the escarpment has on modifying large-scale rainproducing systems in the KwaZulu-Natal Drakensberg.

Effects of plough pan development on surface hydrology and on soil physical properties in Southeastern Brazilian plateau

Conventional tillage may impose changes in soil physical properties that lead to a decrease in soil physical quality. Although plough pan formation is considered to be an important consequence of conventional tillage practices in Southeastern Brazil, few studies have focused on its hydrological consequences. Detailed investigations in two experimental plots located in the hilly landscape of Serra do Mar close to Rio de Janeiro city were carried out to characterize the changes in soil physical properties and in soil hydrology due to plough pan formation. Conventional (CT) and minimum tillage (MT) practices were implemented in two plots for 3 years and soil matric potential (SMP) was monitored in each plot via nests of tensiometers and Watermark® sensors installed at different depths. Undisturbed soil blocks were collected for micromorphological analyses to quantify the total pore space in soils under CT and MT systems, and in soils under natural tropical forest. Results suggest that soils under the CT system developed a plough pan layer at about 20 cm depth that had 44% less total porosity as compared to surface conditions. It is shown that soils under the CT system tended to stay saturated for longer periods of time after each rainfall event. Besides, during intense rainy periods soils under the CT system may develop hydrologic conditions that favor lateral flows while soils under the MT system were still draining. Such hydrological responses may explain why average soil erosion rates measured for individual rainfall events under the CT system were about 2.5 times greater than the ones observed at MT. The results attested that conventional tillage in this area generated modifications in soil fabric, especially in pore-size distribution and connectivity, which induced important changes in soil hydrology and soil erosion. The agricultural practices used in this area, associated with the local steep hillslopes and intense rainfall events, are definitely not adequate and require the introduction of soil and water conservation practices in order to become sustainable.

Rainfall erosivity and rainfall return period in the experimental watershed of Aracruz, in the coastal plain of Espirito Santo, Brazil

Knowledge on the factors influencing water erosion is fundamental for the choice of the best land use practices. Rainfall, expressed by rainfall erosivity, is one of the most important factors of water erosion. The objective of this study was to determine rainfall erosivity and the return period of rainfall in the Coastal Plains region, near Aracruz, a town in the state of Espírito Santo, Brazil, based on available data. Rainfall erosivity was calculated based on historic rainfall data, collected from January 1998 to July 2004 at 5 min intervals, by automatic weather stations of the Aracruz Cellulose S.A company. A linear regression with individual rainfall and erosivity data was fit to obtain an equation that allowed data extrapolation to calculate individual erosivity for a 30-year period. Based on this data the annual average rainfall erosivity in Aracruz was 8,536 MJ mm ha-1 h-1 yr-1. Of the total annual rainfall erosivity 85 % was observed in the most critical period October to March. Annual erosive rains accounted for 38 % of the events causing erosion, although the runoff volume represented 88 % of the total. The annual average rainfall erosivity return period was estimated to be 3.4 years.

Modeling the Distribution of Rainfall Intensity using Hourly Data

Problem statement: Design of storm water best management practices to control runoff and water pollution can be achieved if a prior knowledge of the distribution of rainfall characteristics is known. Rainfall intensity, particularly in tropical climate, plays a major role in the design of runoff conveyance and erosion control systems. This study is aimed to explore the statistical distribution of rainfall intensity for Peninsular Malaysia using hourly rainfall data. Approach: Hourly rainfall data were collected from twelve stations spread across the Peninsular. Six hour separation time was used to divide the data into individual rainfall events and four probability distributions namely, Generalized Pareto (GP), Exponential (EXP), Beta (BT) and Gamma (GM) distributions were used to model the distribution of the hourly rainfall intensity. Kolmogorov-Sminov anderson-Darling and Chi-squared goodness-of-fit tests were used to evaluate the best fit. Results: The rainfall frequency, based on 6 h minimum inter-event time, ranges from 115-198 events. The distribution of the rainfall frequency and that of the highest intensity observed, over the recorded period, across the peninsular, is however irregular. The mean rainfall intensity ranges from 2.32-3.88 mm h-1. Kuala-Lumpur and Penang received the highest, while Segamat and Kedah received the lowest. Conversely, over the period of record, Segamat recorded the highest CV, skewness and kurtosis while Pahang has the least value for these parameters. Goodness-of-fit tests at 5% level of significance indicate that all the models can be used to model the distribution of rainfall intensity in Peninsular Malaysia. However, GP is found to be the most suitable model among the four probability distributions tested. Conclusion: Basic statistics of hourly rain intensity were obtained and probability distributions compared. It was found that GP is the most suitable model. Results can be useful, particularly, to agricultural and storm water management planning.

Performance of high-resolution X-band radar for rainfall measurement in The Netherlands

Abstract. This study presents an analysis of 195 rainfall events gathered with the X-band weather radar SOLIDAR and a tipping bucket rain gauge network near Delft, The Netherlands, between May 1993 and April 1994. The aim of this paper is to present a thorough analysis of a climatological dataset using a high spatial (120 m) and temporal (16 s) resolution X-band radar. This makes it a study of the potential for high-resolution rainfall measurements with non-polarimetric X-band radar over flat terrain. An appropriate radar reflectivity – rain rate relation is derived from measurements of raindrop size distributions and compared with radar – rain gauge data. The radar calibration is assessed using a long-term comparison of rain gauge measurements with corresponding radar reflectivities as well as by analyzing the evolution of the stability of ground clutter areas over time. Three different methods for ground clutter correction as well as the effectiveness of forward and backward attenuation correction algorithms have been studied. Five individual rainfall events are discussed in detail to illustrate the strengths and weaknesses of high-resolution X-band radar and the effectiveness of the presented correction methods. X-band radar is found to be able to measure the space-time variation of rainfall at high resolution, far greater than what can be achieved by rain gauge networks or a typical operational C-band weather radar. On the other hand, SOLIDAR can suffer from receiver saturation, wet radome attenuation as well as signal loss along the path. During very strong convective situations the signal can even be lost completely. In combination with several rain gauges for quality control, high resolution X-band radar is considered to be suitable for rainfall monitoring over relatively small (urban) catchments. These results offer great prospects for the new high resolution polarimetric doppler X-band radar IDRA.

Effects of Two Types of Landfills on River Water Quality and Endocrine Disruptor Concentrations Before and After Rainfall in a Subtropical Climate

Abstract One closed uncontrolled landfill, the Neihu garbage dump, and one active controlled landfill, the Sanzhuku sanitary landfill, were selected for investigation of their leachate characteristics and effects on adjacent river water quality before and after rainfall in northern Taiwan. A total of seven samplings were made during February and June 2007, with four samplings done after individual rainfall events on study sites. Water quality of runoff samples collected from the Sanzhuku sanitary landfill showed less pollution than the water quality of leachates collected from the Neihu garbage dump; however, some water quality levels of leachate samples collected from the Neihu garbage dump were relatively high, such as ammonia nitrogen (NH3-N), orthophosphate (PO43-) and biochemical oxygen demand (BOD5). At the uncontrolled dump, rainfall lead to dilution effects on river water NH3-N and PO43- concentrations, but not other water quality parameters. In contrast, the concentrations of bisphenol A (BPA) and nonylphenol were increased in both types of landfills after rainfall in the present study. Dilution effects of rainfall on most water quality parameters and toxicity tests were observed in the Neihu garbage dump leachates after rainfall, but not for the Sanzhuku Landfill runoff. The highest concentration of BPA measured in this study was 25.8 μg L-1 in the Sanzhuku sanitary landfill runoff after the heaviest rainfall event, during which 236 mm of rainfall accumulated over four days. The results of this study suggest that both uncontrolled and controlled landfill leachates can be an important potential pollution source of BPA to adjacent water bodies.

Control of recent European surface climate change by atmospheric flow

Many changes in European surface climate have occurred over the past decades, but most of the processes driving them are not identified. In particular, the role of atmospheric flow in driving surface trends needs to be evaluated to better predict future regional climate. We compare observed surface climate trends with those constructed from daily flow analogues. We find that during the last 60 years atmospheric circulation changes are the main drivers of surface weather trends in winter, but not in summer where temperature strongly interacts with the water cycle. For instance, increasing anticyclonic conditions control the decreasing summer rainfall frequency, but rainfall amount and cloud cover have not decreased accordingly, because individual rainfall events bring more rain now than decades ago. Over the past three decades the control by atmospheric flow changes has weakened, indicating evolutions in the processes steering European surface climate change.

Controls on the spatial and temporal variability of 222Rn in riparian groundwater in a lowland Chalk catchment

Radon is a powerful tracer of stream–aquifer interactions. However, it is important to consider the source and behaviour of radon in groundwater when interpreting observations of river radon in relation to groundwater discharge. Here we characterise the variability in groundwater radon concentrations in the riparian zone of a Chalk catchment. Groundwater 222 Rn (radon) concentrations were determined in riparian zone boreholes at two sites in the Lambourn catchment, Berkshire, UK, over a 2 year period. In addition, borehole core material was analysed for 226 Ra (radium) and to determine radon emanation. Radon and radium concentrations and radon emanation were found to change with depth and temporal variations in groundwater radon concentrations were found at different scales. The abundance of radium and emanation of radon increased nearer the surface leading to greater groundwater radon concentrations. It is shown that seasonal changes in water table elevation can to lead to variable radon concentrations in groundwater as zones of differing radon production become hydraulically active. Groundwater radon concentrations in shallow piezometers were found to respond to both seasonal changes in the water table and individual rainfall events. Riparian sources of radon can be variable and are therefore potentially influential in the radon signals observed in rivers and should be properly characterised when interpreting river radon inputs.

Event and Continuous Hydrologic Modeling with HEC-HMS

Event hydrologic modeling reveals how a basin responds to an individual rainfall event (e.g., quantity of surface runoff, peak, timing of the peak, detention). In contrast, continuous hydrologic modeling synthesizes hydrologic processes and phenomena (i.e., synthetic responses of the basin to a number of rain events and their cumulative effects) over a longer time period that includes both wet and dry conditions. Thus, fine-scale event hydrologic modeling is particularly useful for understanding detailed hydrologic processes and identifying the relevant parameters that can be further used for coarse-scale continuous modeling, especially when long-term intensive monitoring data are not available or the data are incomplete. Joint event and continuous hydrologic modeling with the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) is discussed in this technical note and an application to the Mona Lake watershed in west Michigan is presented. Specifically, four rainfall events were selected f...