Higher Peak Flow Research Articles

A Model for Developing Reservoir Operation Rules for Irrigation Projects

At a basin scale the criteria for designing reservoirs for irrigation projects are based in three aspects: i) Storage required for supplying crop water requirements at an irrigated area, which are calculated for critical drought conditions. ii) Storage required for releasing the minimum ecological river flow under the described weather condition. iii) Spillway dimensions to evacuate high peak flow events. Those aspects are fundamental for designing a reservoir, however, designing reservoir operation rules is also an important aspect and normally it is a big uncertainty for project managers. This study focuses on developing a mathematical model for operating reservoirs for irrigation projects into an integrated basin context. The crop cycle is simulated for several year based on long term historical hydro-meteorological time series in a daily basis. Irrigation requirements are obtained from those simulations. Those results are clustered in 10-day periods during the crop cycle. Frequency analyses of the irrigation requirements are performed. Those results are applied for building irrigation schedules for dry, normal, and rainy conditions. Furthermore, frequency analyses are performed to the distributed rainfall for determining similar weather thresholds. The reservoir operation consists in first routing the inflow thorough the reservoir to the different outlets. A conceptual hydrological routing model is applied for this purpose. Second, the amount of water to release from the reservoir to the irrigation scheme depends on amount of rainfall measured during the precedent 10-days and on the irrigation schedule for that weather condition. The model was developed for a case study in the Ecuadorian Coast, which is a large irrigation project, called PACALORI. The reservoir operation rules were obtained by modeling the system for 42 years of hydro-meteorological data. The model would be implemented in a real time operation, depending on the monitoring implementation for measuring rainfall, flow, and meteorological variables.

Climate changes of hydrometeorological and hydrological extremes in the Paute basin, Ecuadorean Andes

Abstract. Investigation was made on the climate change signal for hydrometeorological and hydrological variables along the Paute River basin, in the southern Ecuador Andes. An adjusted quantile perturbation approach was used for climate downscaling, and the impact of climate change on runoff was studied for two nested catchments within the basin. The analysis was done making use of long daily series of seven representative rainfall and temperature sites along the study area and considering climate change signals of global and regional climate models for IPCC SRES scenarios A1B, A2 and B1. The determination of runoff was carried out using a lumped conceptual rainfall–runoff model. The study found that the range of changes in temperature is homogeneous for almost the entire region with an average annual increase of approximately +2.0 &degC. However, the warmest periods of the year show lower changes than the colder periods. For rainfall, downscaled results project increases in the mean annual rainfall depth and the extreme daily rainfall intensities along the basin for all sites and all scenarios. Higher changes in extreme rainfall intensities are for the wetter region. These lead to changes in catchment runoff flows, with increasing high peak flows and decreasing low peak flows. The changes in high peak flows are related to the changes in rainfall extremes, whereas the decreases in the low peak flows are due to the increase in temperature and potential evapotranspiration together with the reduction in the number of wet days.

Predicting streamflow for land cover changes in the Upper Gilgel Abay River Basin, Ethiopia: A TOPMODEL based approach

Hydrological effects of land cover changes and runoff contributions from respective land cover types are analysed for the Upper Gilgel Abay basin in Ethiopia. Runoff production and streamflow are simulated by the TOPMODEL approach. For impact assessment of land cover changes, satellite based land covers for the years 1973, 1986 and 2001 are considered. Catchment topography as well as land cover and vegetation characteristics are derived from satellite images and serve to estimate model parameters. Land cover in TOPMODEL has been implemented by spatial units based on the actual size of each land cover type. The topographic index distribution function, which is an important input to the TOPMODEL, is prepared for each land cover type. Simulations are also performed for specific land cover types to allow inter comparison of hydrological responses. Results showed that the highest peak flow as well as the annual streamflow volume varied among the land cover types agriculture, forest and grassland which dominate land cover in the catchment. Results of this study show that in data poor basins, satellite images provide suitable land surface data for rainfall–runoff modelling and land surface parameterization. Findings are of relevance for many African rural catchments which experience rapid population increases and resource scarcity.

Climate change, urban development, and community perception of an extreme flood: A case study of Vernonia, Oregon, USA

Extreme precipitation events and land development on floodplains have been an increasing concern for many regions throughout the world as they increase flood risks. Using the 2007 Vernonia flood in Oregon as a case, this research examined potential changes in future flood risks under the combined climate change and urban development scenarios. Research procedures included hydraulic modeling, social analysis, and scenario analysis. Physical modeling involved creating a model for the 2007 flood, analyzing the results using Hydrologic Engineering Center – Hydrologic Modeling System (HEC-HMS), predicting variation in watershed parameters, and creating accessible maps for the public. Social questionnaires were distributed throughout Vernonia, and the results were analyzed. Our results indicate that increasing urbanization and impervious surface resulted in a major increase in the severity of flooding, exacerbating flood damage by longer inundation time and higher peak flow. The social survey revealed key discrepancies between floodplain residents and non-floodplain residents. The communal strain on the flood victims is independent of whether they lived in the floodplain or not, while floodplain residents perceived higher economic strain, family strain, and physical damage than non-floodplain residents. The information obtained from residents' response to extreme floods, along with the successful reevaluation of flood modeling at a finer scale, buttress the applicability of our procedure for flood inundation studies to other areas. Such methodologies will enhance our ability to predict and mitigate the damaging effect of floods in a changing climate.

Effects of urban form on wadi flow frequency analysis in the Wadi Aday watershed in Muscat, Oman

The effect of urban form on Curve Number (CN) use in rainfall-runoff modelling is explored in an arid wadi watershed in Oman. The standard hydrologic CN used in the Soil Conservation Service method may not be appropriate to use in urbanized arid wadi regions since the land-use characteristics are different than those for which the CN method was developed for. In this paper a new method is described to develop regional CN for arid wadi regions. The modified CN are then used to predict peak-flow and time-to-peak in a wadi watershed and are compared to results from the standard CN method. The regional values produce higher peak-flow (an increase of 19% or 7.4 m3/s, on average) with shorter time-to-peak (a decrease of 16% or 86 minutes, on average), mimicking the flash-floods seen in the region. In addition, the regional CN were used to model the change in hydrology caused by urbanization.

三次元角柱側面に発生する局部負圧に関するLES

The purpose of this paper is to investigate turbulence effects on characteristics of local severe suction on side face of a three-dimensional square cylinder by LES. The behavior of conical vortices associated with local suctions at the angle of the attack =0, and glancing angle are focused on. First, the computed results for distribution of the pressure coefficients are validated through comparison with the experimental data. Next, using the computed results, the effects of inflow turbulence on the high peak suctions and flow characteristics are examined. As a result, high peak suctions occur associated with wake characteristics and flow reattachment characteristics affected by the large scale fluctuation of oncoming turbulence.

Variability in effect of climate change on rain-on-snow peak flow events in a temperate climate

► Historically extreme peak flows in a temperate climate are rain-on-snow events. ► Climate change is predicted to decrease the number of rain-on-snow events. ► The transient rain/snow zone is predicted to increase in elevation with climate change. ► Decreases in rain-on-snow events increased frequency of peak flows <5–10 year return. ► Decreases in rain-on-snow events decreased frequency of peak flows >10 year return. The frequency of rain-on-snow (ROS) hydrologic events, which produce high runoff volumes and lead to large-scale flooding and avalanching, are likely to change in the future as the types and timing of precipitation change. The relationship between ROS precipitation events and peak daily flow events ⩾1-year return were examined for historical and future runoff affected by climate change within the Santiam River Basin, Oregon. Historical streamflow records and modeled historical and future streamflow projections were analyzed for three sites across three elevation zones defined by the dominant precipitation types; rain, rain and snow transition, and snow. The results illustrate that, across elevation zones, historical peak daily flows ⩾1-year return have a high frequency (>60%) of association with ROS. The historical association between peak daily flows and ROS is highest within the transient rain and snow elevation band (350–1100 m), with 80% and 100% of ⩾1 and ⩾5-year return peak flows associated with ROS, respectively. In a future with increased air temperature due to climate change, our results indicate that a decrease in the frequency of high peak flow ROS events will occur in the low and middle elevation zones while the frequency of ROS associated peak flows will increase in high elevation areas. The transition of winter precipitation from snow to rain is predicted to increase peak daily flows <5–10-year return interval and decrease peak daily flows ⩾10-year return in the middle to high elevation zones.

Impact of radar‐rainfall error structure on estimated flood magnitude across scales: An investigation based on a parsimonious distributed hydrological model

The goal of this study is to diagnose the manner in which radar‐rainfall input affects peak flow simulation uncertainties across scales. We used the distributed physically based hydrological model CUENCAS with parameters that are estimated from available data and without fitting the model output to discharge observations. We evaluated the model's performance using (1) observed streamflow at the outlet of nested basins ranging in scale from 20 to 16,000 km2 and (2) streamflow simulated by a well‐established and extensively calibrated hydrological model used by the US National Weather Service (SAC‐SMA). To mimic radar‐rainfall uncertainty, we applied a recently proposed statistical model of radar‐rainfall error to produce rainfall ensembles based on different expected error scenarios. We used the generated ensembles as input for the hydrological model and summarized the effects on flow sensitivities using a relative measure of the ensemble peak flow dispersion for every link in the river network. Results show that peak flow simulation uncertainty is strongly dependent on the catchment scale. Uncertainty decreases with increasing catchment drainage area due to the aggregation effect of the river network that filters out small‐scale uncertainties. The rate at which uncertainty changes depends on the error structure of the input rainfall fields. We found that random errors that are uncorrelated in space produce high peak flow variability for small scale basins, but uncertainties decrease rapidly as scale increases. In contrast, spatially correlated errors produce less scatter in peak flows for small scales, but uncertainty decreases slowly with increasing catchment size. This study demonstrates the large impact of scale on uncertainty in hydrological simulations and demonstrates the need for a more robust characterization of the uncertainty structure in radar‐rainfall. Our results are diagnostic and illustrate the benefits of using the calibration‐free, multiscale framework to investigate uncertainty propagation with hydrological models.

Episodic Change Analysis of the Annual Flood Peak Time Series for a Flood Insurance Study

AbstractDecreasing annual maximum flood peaks on the rivers and streams in the Wisconsin driftless area have been reported in recent studies. Various explanations have been offered, generally suggesting different episodes or change points separating the early periods of higher peak flows from the more recent lower peak flows. The present research used two statistical tests to detect a change point in annual flood peaks at Freeport on the Pecatonica River for the period 1914–2008. Both tests indicated that the most significant change occurred in 1954. Next, to find an explanation for the decreasing peaks, this research carried out a seasonal analysis of flood timing. The decrease in winter flood peaks was partly explained by the decrease in snow depth and the increase in winter temperature, providing less favorable conditions for winter flooding. In turn, the decrease in winter peak flows made once smaller summer peak flows more dominant in recent years, causing the shift in flood timing. Similar analysis ...

Nasal versus oronasal raised volume forced expirations in infants—A real physiologic challenge

Raised volume rapid thoracoabdominal compression (RTC) generates forced expiration (FE) in infants typically from an airway opening pressure of 30 cm H(2)O (V(30)). We hypothesized that the higher nasal than pulmonary airway resistance limits forced expiratory flows (FEF(%)) during (nasal) FE(n), which an opened mouth, (oronasal) FE(o), would resolve. Measurements were performed during a brief post-hyperventilation apnea on 12 healthy infants aged 6.9-104 weeks. In two infants, forced expiratory (FEFV) flow volume (FV) curves were generated using a facemask that covered the nose and a closed mouth, then again with a larger mask with the mouth opened. In other infants (n = 10), the mouth closed spontaneously during FE. Oronasal passive expiration from V(30) generated either the inspiratory capacity (IC) or by activating RTC before end-expiration, the slow vital capacity ((j) SVC). Peak flow (PF), FEF(25), FEF(50), FEF(25-75), FEV(0.4), and FEV(0.5) were lower via FE(n) than FE(o) (P < 0.05), but the ratio of expired volume at PF and forced vital capacity (FVC) as percent was higher (P < 0.05). FEF(75), FEF(85), FEF(90), FVC as well as the applied jacket pressures were not different (P > 0.05). FEFV curves generated via FE(o) exhibited higher PF than FV curves of IC (P < 0.05); PF of those produced via FE(n) were not different from FV curves of IC (P > 0.05) but lower than those of (j) SVC (P < 0.05). In conclusion, the higher nasal than pulmonary airways resistance unequivocally affects the FEFV curves by consistently reducing PF and decreases mid-expiratory flows. A monitored slightly opened mouth and a gentle anterior jaw thrust are physiologically integral for raised volume RTC in order to maximize the oral and minimize nasal airways contribution to FE so that flow limitation would be in the pulmonary not nasal airways.

Produção de água e sedimentos em bacia representativa do semiárido pernambucano

A erosão hídrica é um dos principais processos responsáveis pela degradação física dos solos, em particular em áreas semiáridas, susceptíveis a chuvas de alta intensidade e com limitada cobertura vegetal, principalmente nos períodos secos. O presente trabalho teve como objetivo avaliar experimentalmente as características hidrossedimentológicas da bacia hidrográfica do Riacho Mimoso, no semiárido pernambucano, no município de Pesqueira, PE. A bacia representativa do Riacho Mimoso apresentou respostas hidrológicas com altos picos de vazão, em seção de controle com regime hidrológico intermitente. A produção de descarga sólida em suspensão do Riacho Mimoso é elevada, tendo-se registrado concentrações de sedimentos de 10,91 e 0,91 t ha-1 ano-1, para os anos de 2009 e 2010, respectivamente.

Grey water treatment in upflow anaerobic sludge blanket (UASB) reactor at different temperatures

The treatment of grey water in two upflow anaerobic sludge blanket (UASB) reactors, operated at different hydraulic retention times (HRTs) and temperatures, was investigated. The first reactor (UASB-A) was operated at ambient temperature (14-25 degrees C) and HRT of 20, 12 and 8 h, while the second reactor (UASB-30) was operated at controlled temperature of 30 degrees C and HRT of 16, 10 and 6 h. The two reactors were fed with grey water from 'Flintenbreite' settlement in Luebeck, Germany. When the grey water was treated in the UASB reactor at 30 degrees C, total chemical oxygen demand (CODt) removal of 52-64% was achieved at HRT between 6 and 16 h, while at lower temperature lower removal (31-41%) was obtained at HRT between 8 and 20 h. Total nitrogen and phosphorous removal in the UASB reactors were limited (22-36 and 10-24%, respectively) at all operational conditions. The results showed that at increasing temperature or decreasing HRT of the reactors, maximum specific methanogenic activity of the sludge in the reactors improved. As the UASB reactor showed a significantly higher COD removal (31-64%) than the septic tank (11-14%) even at low temperature, it is recommended to use UASB reactor instead of septic tank (the most common system) for grey water pre-treatment. Based on the achieved results and due to high peak flow factor, a HRT between 8 and 12 h can be considered the suitable HRT for the UASB reactor treating grey water at temperature 20-30 degrees C, while a HRT of 12-24 h can be applied at temperature lower than 20 degrees C.

Understanding the Factors That Influence Headwater Stream Flows in Response to Storm Events1

Stanfield, Les W. and Don A. Jackson, 2011. Understanding the Factors That Influence Headwater Stream Flows in Response to Storm Events. Journal of the American Water Resources Association (JAWRA) 1-22. DOI: 10.1111/j.1752-1688.2010.00518.x Abstract: Headwater drainage features (first- to second-order streams) are the capillaries of the landscape that, among other things, moderate the timing and volumes of water available to the riparian and aquatic ecosystems. How these features respond to summer rainfall is poorly understood. We studied how geology and an index of land use/land cover influenced peak flows following rainfall events in 110 headwater stream sites that were studied over a four-month period during a drought year. Highest peak flows were observed in the most urbanized catchments and in poorly drained soils, but specific responses were variable depending on both geology and land disturbance. Redundancy analysis indicated that both surficial geology and land disturbance were important factors influencing peak flows under drought conditions. We conclude that responses of these headwater streams to individual storms during drought conditions are unpredictable from data collected using our methods, but increased peak flows were associated with increased urban and agricultural development, but mitigated by surficial geology. These findings demonstrate the challenges to accurately predict flow conditions in headwater streams during periods of extreme weather that concurrently have the greatest potential effect on biota. The combination of these challenges and importance of such events indicates the need to develop new approaches to study and manage these resources.

Cerebrospinal fluid and blood flow in mild cognitive impairment and Alzheimer's disease: a differential diagnosis from idiopathic normal pressure hydrocephalus

BackgroundPhase-contrast magnetic resonance imaging (PC-MRI) enables quantification of cerebrospinal fluid (CSF) flow and total cerebral blood (tCBF) flow and may be of value for the etiological diagnosis of neurodegenerative diseases. This investigation aimed to study CSF flow and intracerebral vascular flow in patients with Alzheimer's disease (AD) and patients with amnesic mild cognitive impairment (a-MCI) and to compare the results with patients with idiopathic normal pressure hydrocephalus (NPH) and with healthy elderly volunteers (HEV).MethodsTen a-MCI and 9 mild AD patients were identified in a comprehensive neurological and neuropsychological assessment. They underwent brain MRI; PC-MRI pulse sequence was performed with the following parameters: two views per segment; flip angle: 25° for vascular flow and 20° for CSF flow; field-of-view (FOV): 14 × 14 mm²; matrix: 256 × 128; slice thickness: 5 mm; with one excitation for exams on the 3 T machine, and 2 excitations for the 1.5 T machine exams. Velocity (encoding) sensitization was set to 80 cm/s for the vessels at the cervical level, 10 or 20 cm/s for the aqueduct and 5 cm/s for the cervical subarachnoid space (SAS). Dynamic flow images were analyzed with in-house processing software. The patients' results were compared with those obtained for HEVs (n = 12), and for NPH patients (n = 13), using multivariate analysis.ResultsArterial tCBF and the calculated pulsatility index were significantly greater in a-MCI patients than in HEVs. In contrast, vascular parameters were lower in NPH patients. Cervical CSF flow analysis yielded similar values for all four populations. Aqueductal CSF stroke volumes (in μl per cardiac cycle) were similar in HEVs (34 ± 17) and AD patients (39 ± 18). In contrast, the aqueductal CSF was hyperdynamic in a-MCI patients (73 ± 33) and even more so in NPH patients (167 ± 89).ConclusionOur preliminary data show that a-MCI patients present with high systolic arterial peak flows, which are associated with higher mean total cerebral arterial flows. Aqueductal CSF oscillations are within normal range in AD and higher than normal in NPH. This study provides an original dynamic vision of cerebral neurodegenerative diseases, consistent with the vascular theory for AD, and supporting primary flow disturbances different from those observed in NPH.

Flow-balanced expiration reduces oedema formation in a porcine oleic acid lung injury model

Positive pressure ventilation involves ventilator-controlled inflation of the lungs followed by passive expiration driven by the elastic recoil forces of the respiratory system. In contrast to inspiration where the flow is controlled by the ventilator, expiration is passive, and the only clinically available means of influencing expiration is positive end-expiratory pressure (PEEP). During passive expiration, the flow curve starts with a high peak flow followed by an exponential decay in airflow rate so that typically there is no flow during more than 50% of expiration time. Prolonging the phase of expiratory flow may be expected to be lung protective.

Localized Control of Exsanguinating Arterial Hemorrhage: An Experimental Model

To develop an arterial injury model for testing hemostatic devices at well-defined high and low bleeding rates. A side-hole arterial injury was created in the carotid artery of sheep. Shed blood was collected in a jugular venous reservoir and bleeding rate at the site of arterial injury was controlled by regulating outflow resistance from the venous reservoir. Two models were studied: uncontrolled exsanguinating hemorrhage and bleeding at controlled rates with blood return to maintain hemodynamic stability. Transcutaneous Duplex ultrasound was used to characterize ultrasound signatures at various bleeding rates. A 2.5 mm arterial side-hole resulted in exsanguinating hemorrhage with an initial bleeding rate of 400 ml/min which, without resuscitation, decreased to below 100 ml/min in 5 minutes. After 17 minutes, bleeding from the injury site stopped and the animal had lost 60% of total blood volume. Reinfusion of shed blood maintained normal hemodynamics and both high and low bleeding rates could be maintained without hemorrhagic shock. Bleeding rate at the arterial injury site was held at 395±78 ml/min for 8 minutes, 110±11 ml/min for 15 minutes, and 12±1 ml/min for 12 minutes. Doppler flow signatures at the site of injury were characterized by high peak and end-diastolic flow velocities at the bleeding site which varied with the rate of hemorrhage. We have developed a hemodynamically stable model of acute arterial injury which can be used to evaluate diagnostic and treatment methods focused on control of the arterial injury site.

Incorporating Surface Storage and Slope to Estimate Clark Unit Hydrographs for Ungauged Indiana Watersheds

Application of Soil Conservation Service’s (SCS) dimensionless unit hydrograph method for ungauged basins in Indiana yields very high peak flows and short time to peaks for the northern region, thus producing unrealistic flow estimates for design purposes. It is hypothesized that the overestimation of peak flows in northern region using SCS method is due to the flat terrain and high surface storage caused by the Wiconsinan glaciations. To incorporate the slope and storage characteristics, the application of Clark synthetic unit hydrograph (SUH), which incorporates time of concentration ( tc ) and a storage parameter (R) to produce runoff hydrograph, is explored for Indiana. A statistical analysis of 29 geomorphic attributes and past storm hydrographs for thirty watersheds in Indiana show that watersheds in north, central and southern regions are statistically different in terms of slope and storage characteristics. A statistical comparison of Clark parameters ( R and tc ) estimated for past storm events a...

Urban flood hazard zoning in Tucumán Province, Argentina, using GIS and multicriteria decision analysis

Recently, the cities of Yerba Buena and Tucuman in Tucumán Province, Argentina, have been affected by several storm flood events, causing hundreds of people to be evacuated from their homes . Heavy intensity rainfall, new housing developments covering previously permeable grounds, and old drainage systems are the main causes for this situation. This paper presents a simple approach of urban flood hazard assessment in a region where primary data are scarce. The objectives of this study are to develop a GIS-aided urban flood hazard zoning of the two cities applying multicriteria decision analysis and to evaluate it by means of uncertainty and sensitivity analysis. The research methodology focused on the analysis of those variables that control the water routing when high peak flows exceed the drainage-system capacity. The model incorporates five parameters: distance to the drainage channels, topography (heights and slopes), ground water table depths, and urban land use. A final hazard map for each category is obtained using an algorithm that combines factors in weighted linear combinations. The urban flood hazard map shows that the southeast part of San Miguel de Tucumán has the highest flood hazard over an extended area as a consequence of the conjunction of lowlands with slopes under 0.6% and the presence of urban stream channels with poor maintenance plan. In this area, several neighbourhoods have been flooded. The model was evaluated by the error propagation method and global sensitivity analysis to assess the uncertainty and the relative importance of model input factors. Finally, the influence of criterion weights are analyzed ranging from 25% to 75% of their original values showing a robust behaviour.

Urban Ecosystems: Alterations to Peakflow, Microclimate and the Natural Environment

More than half of the world’s population now lives in urbanized ecosystems. Continued human population growth over the next several decades will place unprecedented demand on urban water resources, resulting in escalating water quality and supply challenges. Urbanization exacts significant impacts on stream ecosystems including increased magnitude and frequency of peak flows, altered microclimates and reduced biodiversity. Increased impervious surface area in urban settings reduces or eliminates soil infiltration and increases the amount of stormwater runoff delivered to stream channels. Stormwater routing networks in urban areas channelize runoff, reducing stormwater transit time. Stormwater flow serves as an important transport mechanism for non-point source pollutants, and impervious surfaces serve as conduits to flow, replacing soils and vegetation that would otherwise attenuate runoff and transport of pollutants. Stream channels typically broaden and deepen in response to increased volume, velocity and frequency of peak flows, leading to increased channel instability, accelerated erosion, and subsequent loss of habitat. Given these scenarios, urbanization can degrade freshwater resources, detrimentally impact in-stream and riparian biota, and destroy riparian wetland form and function. The following work quantifies peak flow and microclimate alteration due to urbanization in a large, multi-use watershed of the central U.S. A long-term stream flow monitoring program was established in the Hinkson Creek Watershed located in Boone County, mid-Missouri during the fall of 2008. Hydroclimate stations were installed at five locations along Hinkson Creek within predominantly forest, cropland, and urban environments. Continuous stream stage and flow data from these sites were used to quantify peak flow in different environments of the watershed. Preliminary results indicate that forested environments tend to attenuate peak flows from small precipitation events (< 0.80 mm), whereas events of similar magnitude in urban settings cause spikes in flow and a flashier hydrograph. With larger precipitation events (> 1.0 mm), the time from peak rainfall to peak flow is decreased by as much as 13% in urban settings accompanied by at least 4 cm higher peak flows and 15-20% greater flow volume. Average air temperatures in the urban region exceed the forested region by at least 15% during winter months, holding important implications for snow melt and runoff, peak flow and ecosystem processes. Continued monitoring and analyses will more precisely quantify the effects of urbanization on these phenomena and will provide critical information for the sustainable management of urban natural resources.

Urban Ecosystems: Alterations to Peakflow, Microclimate and the Natural Environment

AbstractMore than half of the world’s population now lives in urbanized ecosystems. Continued human population growth over the next several decades will place unprecedented demand on urban water resources, resulting in escalating water quality and supply challenges. Urbanization exacts significant impacts on stream ecosystems including increased magnitude and frequency of peak flows, altered microclimates and reduced biodiversity. Increased impervious surface area in urban settings reduces or eliminates soil infiltration and increases the amount of stormwater runoff delivered to stream channels. Stormwater routing networks in urban areas channelize runoff, reducing stormwater transit time. Stormwater flow serves as an important transport mechanism for non-point source pollutants, and impervious surfaces serve as conduits to flow, replacing soils and vegetation that would otherwise attenuate runoff and transport of pollutants. Stream channels typically broaden and deepen in response to increased volume, velocity and frequency of peak flows, leading to increased channel instability, accelerated erosion, and subsequent loss of habitat. Given these scenarios, urbanization can degrade freshwater resources, detrimentally impact in-stream and riparian biota, and destroy riparian wetland form and function. The following work quantifies peak flow and microclimate alteration due to urbanization in a large, multi-use watershed of the central U.S. A long-term stream flow monitoring program was established in the Hinkson Creek Watershed located in Boone County, mid-Missouri during the fall of 2008. Hydroclimate stations were installed at five locations along Hinkson Creek within predominantly forest, cropland, and urban environments. Continuous stream stage and flow data from these sites were used to quantify peak flow in different environments of the watershed. Preliminary results indicate that forested environments tend to attenuate peak flows from small precipitation events (&lt; 0.80 mm), whereas events of similar magnitude in urban settings cause spikes in flow and a flashier hydrograph. With larger precipitation events (&gt; 1.0 mm), the time from peak rainfall to peak flow is decreased by as much as 13% in urban settings accompanied by at least 4 cm higher peak flows and 15-20% greater flow volume. Average air temperatures in the urban region exceed the forested region by at least 15% during winter months, holding important implications for snow melt and runoff, peak flow and ecosystem processes. Continued monitoring and analyses will more precisely quantify the effects of urbanization on these phenomena and will provide critical information for the sustainable management of urban natural resources.