Catchment Flood Research Articles

Rain-on-snow events, floods and climate change in the Alps: Events may increase with warming up to 4 °C and decrease thereafter

This paper focuses on the influence of mountain rain-on-snow (ROS) events that can on occasion trigger major floods in alpine catchments. In order to assess the evolution of these events in a recent past, and the potential changes that could be experienced in a changing climate over coming decades, we have focused on a small catchment in north-eastern Switzerland, the Sitter, well-endowed with both climate and hydrological data. Observations show that there has been an increase in the number of rain-on-snow events since the early 1960s related to the rise in atmospheric temperatures. Results from a simple temperature-based snow model show that the number of ROS events could increase by close to 50% with temperatures 2–4°C warmer than today, before declining when temperatures go beyond 4°C. The likelihood of more ROS events suggests that the risks of flooding in a future climate may indeed get worse before they improve.

IMPLEMENTASI PERATURAN DAERAH NO 14 TAHUN 2011 TENTANG RENCANA TATA RUANG DAN WILAYAH KOTA SEMARANG DI KECAMATAN TEMBALANG

Flooding in the City of Semarang derived from two sources that is from the sea and from the top of semarang. Regional Semarang over are prioritized for this flood catchment area is established building houses, simple and elite houses. One of the effort from the City Government Semarang by the application of Local Regulation no. 14 years 2011 about spatial plans and the areas of the City of Semarang. This research was conducted in DKTP Semarang as officer of Semarang’s Government. Section of Regional planing and supervision as stakeholder of the Implementation Of The Local Regulation No 14 2011. This Research is based on the rise of the construction of housing in the area of the City of Semarang over especially in Kecamatan Tembalang is not in reflect with RTRW of Semarang City. The purpose of this research is described and analyze Implementation Of Regulation No 14 2011 and analyze what factors which influence the Implementation Of Regulation No 14 2011 the City of Semarang. The results of the study showed that in its implementation there are a number of things can restrickting the implementation of this local regulations. This is due to a lack of human resources , obscurity standards and target of this policy and the less participation of the community and private sectors caused by social and economic conditions. Recommendations from this research are to recruit of human resources to handling the problem , the implementation of RDRTK as a continuity of Semarang’s RTRW , and listen to public aspiration.

A NEAR-GLOBAL BARE-EARTH DEM FROM SRTM

The near-global elevation product from NASA’s Shuttle Radar Topographic Mission (SRTM) has been widely used since its release in 2005 at 3 arcsecond resolution and the release of the 1 arcsecond version in late 2014 means that the full potential of the SRTM DEM can now be realised. However the routine use of SRTM for analytical purposes such as catchment hydrology, flood inundation, habitat mapping and soil mapping is still seriously impeded by the presence of artefacts in the data, primarily the offsets due to tree cover and the random noise. This paper describes the algorithms being developed to remove those offsets, based on the methods developed to produce the Australian national elevation model from SRTM data. <br><br> The offsets due to trees are estimated using the GlobeLand30 (National Geomatics Center of China) and Global Forest Change (University of Maryland) products derived from Landsat, along with the ALOS PALSAR radar image data (JAXA) and the global forest canopy height map (NASA). The offsets are estimated using several processes and combined to produce a single continuous tree offset layer that is subtracted from the SRTM data. <br><br> The DEM products will be made freely available on completion of the first draft product, and the assessment of that product is expected to drive further improvements to the methods.

Institutional adaptive capacities to promote Ecosystem-based Adaptation (EbA) to flooding in England

Purpose – The purpose of this paper is to assess the inherent adaptive capacities of multilevel flood management institutions in England that are necessary to espouse the concept of Ecosystem-based Adaptation (EbA). Design/methodology/approach – This paper is based on an extensive assessment of flood management literature including European and English flood management policies, strategies, regulations and reports. First, an assessment protocol was developed from systematic literature search and, second, multilevel flood management policies and organizations were evaluated. A qualitative scoring method was applied at the assessment stage. Findings – The protocol included 18 major assessment criteria under seven EbA principles. Application of the protocol showed that English national flood policies showed comparatively greater adaptive capacities than European- and local-level policies and local organizations. Specialized flood management policies such as Catchment Flood Management Policies at the local level and European Policies such as flood directives are among the lowest-scoring policy institutions. It was also identified that there is an emerging trend of stakeholder participation, catchment-based approach and knowledge-based adaptation planning at the national level which potentially can be the entry points of wider-scale EbA implementation. This paper recommends proactive roles of local executive organizations through improving institutional communication, consideration of catchment-scale planning with clear adaptation goals and valuing local knowledge base. Originality/value – The research is important to identify the institutional aspects of adaptive capacity that require attention for promoting alternative adaptation measures such as EbA.

Journal of Flood Risk Management

Journal of Flood Risk Management

Improving flood forecasting capability of physically based distributed hydrological models by parameter optimization

Abstract. Physically based distributed hydrological models (hereafter referred to as PBDHMs) divide the terrain of the whole catchment into a number of grid cells at fine resolution and assimilate different terrain data and precipitation to different cells. They are regarded to have the potential to improve the catchment hydrological process simulation and prediction capability. In the early stage, physically based distributed hydrological models are assumed to derive model parameters from the terrain properties directly, so there is no need to calibrate model parameters. However, unfortunately the uncertainties associated with this model derivation are very high, which impacted their application in flood forecasting, so parameter optimization may also be necessary. There are two main purposes for this study: the first is to propose a parameter optimization method for physically based distributed hydrological models in catchment flood forecasting by using particle swarm optimization (PSO) algorithm and to test its competence and to improve its performances; the second is to explore the possibility of improving physically based distributed hydrological model capability in catchment flood forecasting by parameter optimization. In this paper, based on the scalar concept, a general framework for parameter optimization of the PBDHMs for catchment flood forecasting is first proposed that could be used for all PBDHMs. Then, with the Liuxihe model as the study model, which is a physically based distributed hydrological model proposed for catchment flood forecasting, the improved PSO algorithm is developed for the parameter optimization of the Liuxihe model in catchment flood forecasting. The improvements include adoption of the linearly decreasing inertia weight strategy to change the inertia weight and the arccosine function strategy to adjust the acceleration coefficients. This method has been tested in two catchments in southern China with different sizes, and the results show that the improved PSO algorithm could be used for the Liuxihe model parameter optimization effectively and could improve the model capability largely in catchment flood forecasting, thus proving that parameter optimization is necessary to improve the flood forecasting capability of physically based distributed hydrological models. It also has been found that the appropriate particle number and the maximum evolution number of PSO algorithm used for the Liuxihe model catchment flood forecasting are 20 and 30 respectively.

Catchment-scale High-resolution Flash Flood Simulation Using the GPU-based Technology

A number of studies have predicted more frequent and intensive storms as a result of climate change in UK and other parts of the world, which may consequently cause more hazardous flash floods in steep catchments of small to medium size (e.g. up to 100km2). These flash floods are commonly characterized by high-velocity overland flow as a result of rapid catchment response to the intense rainfall. The hydrological processes related to the rapid catchment response are poorly understood and reliable prediction is generally beyond the capability of traditional hydrological models or simplified hydrodynamic models. This work aims to present a shock-capturing hydrodynamic modelling system to simulate the complex rainfall-runoff and the subsequent flash surface flooding process in a rapid-response catchment. The model solves the fully 2D shallow water equations using a finite volume Godunov-type shock-capturing numerical scheme for the rapidly varying overland flow hydrodynamics following intense rainfall. Typically, this type of shock-capturing hydrodynamic models is not able to provide efficient and high-resolution simulations for large-scale flash flood events due to their high computational demand. In order to substantially improve the computational efficiency and enable catchment-scale simulations at very high resolution involving millions of computational nodes, the model is implemented on GPUs for high-performance parallel computing. After being validated against the analytical benchmark of Tilted V-catchment test, the GPU-accelerated hydrodynamic modelling system is applied to simulate the rainfall-runoff process in the 42km2 Haltwhistle Burn Catchment in England.

Review of the flood risk management system in Germany after the major flood in 2013

Widespread flooding in June 2013 caused damage costs of €6 to 8 billion in Germany, and awoke many memories of the floods in August 2002, which resulted in total damage of €11.6 billion and hence was the most expensive natural hazard event in Germany up to now. The event of 2002 does, however, also mark a reorientation toward an integrated flood risk management system in Germany. Therefore, the flood of 2013 offered the opportunity to review how the measures that politics, administration, and civil society have implemented since 2002 helped to cope with the flood and what still needs to be done to achieve effective and more integrated flood risk management. The review highlights considerable improvements on many levels, in particular (1) an increased consideration of flood hazards in spatial planning and urban development, (2) comprehensive property-level mitigation and preparedness measures, (3) more effective flood warnings and improved coordination of disaster response, and (4) a more targeted maintenance of flood defense systems. In 2013, this led to more effective flood management and to a reduction of damage. Nevertheless, important aspects remain unclear and need to be clarified. This particularly holds for balanced and coordinated strategies for reducing and overcoming the impacts of flooding in large catchments, cross-border and interdisciplinary cooperation, the role of the general public in the different phases of flood risk management, as well as a transparent risk transfer system. Recurring flood events reveal that flood risk management is a continuous task. Hence, risk drivers, such as climate change, land-use changes, economic developments, or demographic change and the resultant risks must be investigated at regular intervals, and risk reduction strategies and processes must be reassessed as well as adapted and implemented in a dialogue with all stakeholders.

A vertical wind structure that leads to extreme rainfall and major flooding in southeast Australia

Here we examine winds associated with extreme rainfall and major flooding in coastal catchments and more broadly over southeastern Australia. Both radio-sonde and re-analysis data are examined. In every case (i) atmospheric moisture content is high and (ii) the low-level winds are onshore, and in almost every case (iii) the wind-direction turns anti-cyclonically with increasing height up to 500 hPa. Data from Brisbane extending back more than 50 years is consistent with this behavior: winds turn anti-cyclonically with increasing height on days with heavy rainfall, whereas winds turn cyclonically with increasing height on days with light or no rainfall. In the coastal zone, extreme rainfall rarely occurs without (i), (ii) and (iii). In eastern Australia beyond the coastal zone, conditions (i) and (iii) are also associated with extreme rainfall. We found very few cases where such conditions were not associated with extreme rainfall in this broader region. This study extends previous work by showing that the link between turning winds and rainfall exists in both the tropics and subtropics, and the link applies in cases of extreme rainfall and associated major flooding.

Combined Fluvial and Pluvial Flood Inundation Modelling for a Project Site

There are many sources of flooding viz. river flooding, coastal flooding, surface water flooding, drain and sewer flooding, groundwater flooding etc. This study envisages identification of various flooding sources, estimation of maximum floods and their routing through drainage system for a proposed industrial site. The digital elevation model (DEM) is developed from DGPS points, 0.5 m interval contour and spot levels and contours extracted from survey of India topographical maps for the surrounding area. The L-moments based rainfall frequency analysis has been performed to estimate 1 day maximum rainfall for various return periods. The synthetic unit hydrographs are derived from catchment characteristics and flood hydrographs for 10, 25, 50 and 100 year return periods are computed. The two major source of flooding are: flow in the drain and rainfall induced catchment flooding are modelled using MIKE FLOOD package. The bathymetry of the flood plain around the plant site at 5 m grid size is created from DEM in the 2-D modelling in MIKE-21. Local rainfall over the proposed industrial site is also modelled in the MIKE-21. The spills from drainage network due to upstream catchment flow and local rainfall are simulated in coupled MILE-11 and MIKE-21 i.e., MIKE FLOOD package. Various scenarios of flooding like flow in the drain and with and without rainfall of various return periods are simulated to develop corresponding flood inundation maps. Other parameters like flood extent, depth, level, duration and maximum flow velocity are also computed. The safe grade levels for the industrial site are proposed considering these parameters to safe guard the flood disaster.

Reducing uncertainty in small-catchment flood peak estimation

Every year in the UK, many flood risk assessments are carried out on small catchments, typically draining areas of less than 25 km2 . Standard hydrological practice in all UK catchments is to apply the methods presented in the Flood Estimation Handbook (FEH) and its subsequent updates. FEH methods are practical, relatively easy to apply and based on extensive statistical analyses. However, uncertainties can be large, especially in atypical catchments, and small catchments can present unique challenges in terms of heavy urbanisation and rapid flood responses. Compared to larger catchments, small catchment flood data are limited. In this study, we use a dataset of annual maxima and digital catchment descriptors at 205 small catchments to benchmark the QMED and Q100 estimation performance of current UK flood estimation methods: the FEH statistical method, ReFH2 and MacDonald and Fraser’s method, in rural and urbanised catchments separately. All methods perform similarly in rural catchments overall, although MacDonald and Fraser’s method underestimates QMED in urbanised catchments. The methods show a larger factorial standard error against this small catchment dataset than they do against typical datasets of mixed-size catchments. Further work will evaluate the performance of ReFH2 in combination with the latest FEH13 rainfall model.

Estimating Extreme Spatial Rainfall Intensities

AbstractDetermining the impact of catchment flooding requires an estimate of extreme spatial rainfall intensity. Current flood design practice typically converts a point estimate of rainfall intensity into a spatial rainfall intensity using an areal reduction factor, assumed constant across an entire region. Areal reduction factors do not explicitly consider regional variations in extreme rainfall. Here, a new approach for spatial estimates of extreme rainfall is introduced that directly incorporates the spatial area (A) into an intensity-frequency-duration relationship (IFD). This IFDA approach uses spatial rainfall fields to overcome shortcomings of the areal reduction factor by explicitly incorporating spatial variations in the extreme rainfall intensity. The IFDA approach is evaluated for 11 case study regions in Australia, across climates (tropical to Mediterranean), areas (25–7,225 km2), durations (1–4 days), and average recurrence intervals (ARI 2–100 years). The change in extreme spatial rainfall...

Flood triggering in Switzerland: the role of daily to monthly preceding precipitation

Abstract. Determining the role of different precipitation periods for peak discharge generation is crucial for both projecting future changes in flood probability and for short- and medium-range flood forecasting. In this study, catchment-averaged daily precipitation time series are analyzed prior to annual peak discharge events (floods) in Switzerland. The high number of floods considered – more than 4000 events from 101 catchments have been analyzed – allows to derive significant information about the role of antecedent precipitation for peak discharge generation. Based on the analysis of precipitation times series, a new separation of flood-related precipitation periods is proposed: (i) the period 0 to 1 day before flood days, when the maximum flood-triggering precipitation rates are generally observed, (ii) the period 2 to 3 days before flood days, when longer-lasting synoptic situations generate "significantly higher than normal" precipitation amounts, and (iii) the period from 4 days to 1 month before flood days when previous wet episodes may have already preconditioned the catchment. The novelty of this study lies in the separation of antecedent precipitation into the precursor antecedent precipitation (4 days before floods or earlier, called PRE-AP) and the short range precipitation (0 to 3 days before floods, a period when precipitation is often driven by one persistent weather situation like e.g., a stationary low-pressure system). A precise separation of "antecedent" and "peak-triggering" precipitation is not attempted. Instead, the strict definition of antecedent precipitation periods permits a direct comparison of all catchments. The precipitation accumulating 0 to 3 days before an event is the most relevant for floods in Switzerland. PRE-AP precipitation has only a weak and region-specific influence on flood probability. Floods were significantly more frequent after wet PRE-AP periods only in the Jura Mountains, in the western and eastern Swiss plateau, and at the outlet of large lakes. As a general rule, wet PRE-AP periods enhance the flood probability in catchments with gentle topography, high infiltration rates, and large storage capacity (karstic cavities, deep soils, large reservoirs). In contrast, floods were significantly less frequent after wet PRE-AP periods in glacial catchments because of reduced melt. For the majority of catchments however, no significant correlation between precipitation amounts and flood occurrences is found when the last 3 days before floods are omitted in the precipitation amounts. Moreover, the PRE-AP was not higher for extreme floods than for annual floods with a high frequency and was very close to climatology for all floods. The fact that floods are not significantly more frequent nor more intense after wet PRE-AP is a clear indicator of a short discharge memory of Pre-Alpine, Alpine and South Alpine Swiss catchments. Our study poses the question whether the impact of long-term precursory precipitation for floods in such catchments is not overestimated in the general perception. The results suggest that the consideration of a 3–4 days precipitation period should be sufficient to represent (understand, reconstruct, model, project) Swiss Alpine floods.

The relative role of hillslope and river network routing in the hydrologic response to spatially variable rainfall fields

This paper introduces a new methodology and a rainfall spatial organisation index to examine the relative role of hillslope and channel residence times in the analysis of the significance of spatial rainfall representation in catchment flood response modelling. The relationship between the flood response, the hillslope and channel residence time representation and the spatial organisation of the rainfall fields is obtained by extending the ‘spatial moments of catchment rainfall’ statistics (Zoccatelli et al., 2011) to the hillslope system. The flood prediction error generated by assuming spatially uniform rainfall is related to the spatial organisation of the rainfall fields by means of the scaled spatial moment of order one for the channel network and the hillslope system. The methodology provides a basis for a more general consideration of the relationship between the flood response dependence to spatial rainfall organisation and catchment size. The methodology is illustrated based on data from five extreme flash floods occurred in various European regions in the period 2002–2007. Discharge data are available either from streamgauges or from post-flood surveys for 27 catchments, ranging in size between 36 and 982km2. High space–time resolution radar rainfall fields are also available for the analyses. These data are used to implement a distributed hydrological model simulating the runoff generation by infiltration excess and explicitly representing the surface flow paths across both the hillslopes and the river network. The hydrological model is alternatively forced with spatially-distributed and spatially-uniform rainfall input, to analyse the factors controlling the sensitivity of the model output to the spatial rainfall data. Our results show that the spatial variability of the rainfall can influence the flash-flood hydrographs for catchments as small as 50km2, and that the dependence of flood hydrograph shape to spatial rainfall variability cannot be treated as scale dependent relative to the size of the catchment.The rainfall index can be exploited as similarity index for classifying catchments and flood events according to the hillslopes/channel residence times and to provide guidance on the space and time resolution of the rainfall monitoring system required to predict the flood response.

Urban flood simulation based on the SWMM model

Abstract. China is the nation with the fastest urbanization in the past decades which has caused serious urban flooding. Flood forecasting is regarded as one of the important flood mitigation methods, and is widely used in catchment flood mitigation, but is not widely used in urban flooding mitigation. This paper, employing the SWMM model, one of the widely used urban flood planning and management models, simulates the urban flooding of Dongguan City in the rapidly urbanized southern China. SWMM is first set up based on the DEM, digital map and underground pipeline network, then parameters are derived based on the properties of the subcatchment and the storm sewer conduits; the parameter sensitivity analysis shows the parameter robustness. The simulated results show that with the 1-year return period precipitation, the studied area will have no flooding, but for the 2-, 5-, 10- and 20-year return period precipitation, the studied area will be inundated. The results show the SWMM model is promising for urban flood forecasting, but as it has no surface runoff routing, the urban flooding could not be forecast precisely.

Improving operational flood ensemble prediction by the assimilation of satellite soil moisture: comparison between lumped and semi-distributed schemes

Abstract. Assimilation of remotely sensed soil moisture data (SM-DA) to correct soil water stores of rainfall-runoff models has shown skill in improving streamflow prediction. In the case of large and sparsely monitored catchments, SM-DA is a particularly attractive tool. Within this context, we assimilate satellite soil moisture (SM) retrievals from the Advanced Microwave Scanning Radiometer (AMSR-E), the Advanced Scatterometer (ASCAT) and the Soil Moisture and Ocean Salinity (SMOS) instrument, using an Ensemble Kalman filter to improve operational flood prediction within a large (> 40 000 km2) semi-arid catchment in Australia. We assess the importance of accounting for channel routing and the spatial distribution of forcing data by applying SM-DA to a lumped and a semi-distributed scheme of the probability distributed model (PDM). Our scheme also accounts for model error representation by explicitly correcting bias in soil moisture and streamflow in the ensemble generation process, and for seasonal biases and errors in the satellite data. Before assimilation, the semi-distributed model provided a more accurate streamflow prediction (Nash–Sutcliffe efficiency, NSE = 0.77) than the lumped model (NSE = 0.67) at the catchment outlet. However, this did not ensure good performance at the "ungauged" inner catchments (two of them with NSE below 0.3). After SM-DA, the streamflow ensemble prediction at the outlet was improved in both the lumped and the semi-distributed schemes: the root mean square error of the ensemble was reduced by 22 and 24%, respectively; the false alarm ratio was reduced by 9% in both cases; the peak volume error was reduced by 58 and 1%, respectively; the ensemble skill was improved (evidenced by 12 and 13% reductions in the continuous ranked probability scores, respectively); and the ensemble reliability was increased in both cases (expressed by flatter rank histograms). SM-DA did not improve NSE. Our findings imply that even when rainfall is the main driver of flooding in semi-arid catchments, adequately processed satellite SM can be used to reduce errors in the model soil moisture, which in turn provides better streamflow ensemble prediction. We demonstrate that SM-DA efficacy is enhanced when the spatial distribution in forcing data and routing processes are accounted for. At ungauged locations, SM-DA is effective at improving some characteristics of the streamflow ensemble prediction; however, the updated prediction is still poor since SM-DA does not address the systematic errors found in the model prior to assimilation.

Frequency, predisposition, and triggers of floods in flysch Carpathians: regional study using dendrogeomorphic methods

Dangerous overland flood events in the foothills of the flysch Carpathians often result from a cumulative effect of floods in high-gradient channels. Detailed understanding of the origin of floods in these catchments is only possible if the occurrence of these floods in the past has thoroughly been studied. Yet, no gauging stations can be found in the local catchments. The reconstruction of floods in ungauged catchments has so far been performed using dendrogeomorphic methods. Stems or branches floating in the floodwater can affect stems or roots of living trees and injure them. Trees are able to record these signals in their tree-ring series. Within the flysch Carpathians, the floods have been reconstructed based on the analysis of 446 cross sections from scarred tree roots and 192 increment cores from the stems of affected trees in the studied area of 10 catchments surrounding the highest peak of the Moravskoslezské Beskydy Mts, the Lysá hora Mt. The dating comprised 64 floods (in different catchments) in 28 flood years for the maximal period of 1883–2012. Most catchments (nine out of ten) were affected by floods in the year 1997. Above-average frequency of floods has also been found for the last two decades, namely thanks to numerous samples taken from young tree roots that revealed more flood impacts. By contrast, although tree-ring series enabled the reconstruction of a longer time series, they only recorded the major floods.The most significant factor affecting the frequency of floods is the orientation of catchments toward the prevailing wind direction. Positive influence of catchment gradient on flood frequency and higher occurrence of floods in the period of intensive slope deforestation show that the floods of the 1950s to 1970s could have a character of flash floods. This assumption is also supported by the character of probable triggering precipitation (high magnitude–short duration precipitation) of this period. Generally, the most frequent probable triggering factor is, however, an above-average seven-day precipitation amount, which indicates — along with the positive relation between the catchment extent and flood frequency — that a majority of floods hardly ever occur as an immediate response to one-day precipitation extremes. Fast spring melting of thick snow cover plays an insignificant role in floods in the studied medium–high mountains.

Pitfalls in developing coastal climate adaptation responses

Increasing awareness of the risks to coastal communities and infrastructure posed by sea level rise and possible climate-induced changes to the frequency and intensity of catchment flooding events have triggered a large number of studies that have assessed the risk, and developed a prioritisation of actions. These prioritised action recommendations are typically encapsulated in climate adaptation plans and pathways documents, risk reduction strategies, and climate action plans. These studies typically involve a vulnerability assessment task and an action prioritisation task, often performed in the same study. Most of the focus on research and method development over recent decades has been on the first task that aims to quantify the vulnerability of coastal communities and infrastructure. It is argued here that as a result of this emphasis on assessing vulnerability, at the cost of adequate consideration of response actions, along with the linear ‘fix and forget’ management approach to climate adaptation, has led to a lack of uptake in coastal climate adaptation studies and strategies. To this end the aim of the work presented here is to highlight common shortfalls in this fix and forget approach and in particular in the response prioritisation task. Ways that these shortfalls can be avoided, based on knowledge from decision theory, are presented.

Methodology for flood frequency estimations in small catchments

Abstract. Estimations of flood frequencies in small catchments are difficult due to a lack of measured discharge data. This problem is usually solved in the Czech Republic by hydrologic modelling when there is a reason not to use the data provided by the Czech hydrometeorological institute, which are quite expensive and have a very low level of accuracy. Another way is to use a simple method which provides sufficient estimates of flood frequency based on the available spatial data. A new methodology is being developed considering all important factors affecting flood formation in small catchments. The relationship between catchment descriptors and flood characteristics has been analysed first to get an overview of the importance of each considered descriptor. The results for different descriptors vary from a highly correlated relationship of an expected shape to a relationship which is opposite to that expected, mainly in the case of land use. The parameterisation of the methodology is also presented, including the sensitivity tests on each involved catchment descriptor and cross-validation of achieved results. In its present form, the methodology achieves an Radj2 value of about 0.61 for 10- and 0.60 for 100-year return periods.

English

The ancient Benin moat of 2.00 to 5.00 m width, and 10 to 30 m depth almost concentrically dug round the City, is supposed to be an important socio-cultural artifact if well preserved. It has served its good purpose of defense and protection of the ancient Bini civilization. Now, modern urbanization pressure has defaced and is degrading the moat and its environs through house development, soil quarrying, gullying, flood catchment, and waste disposal. Because of its extent, it is pertinent to understand its pedo-geological and hydrogeological setting in order to assess the impact of the waste disposal on the soil and groundwater systems. Random; 11 soil (pool) samples at 0.0 to 0.5 m depth, and eight groundwater samples from pumping boreholes, 0.5 to 10.0 m on both sides of the moat were drawn. Samples were analyzed for their chemical, heavy metal constituents (including microbial in water). Comparisons of means with pristine locations in previous studies were conducted using one way analysis of variance (ANOVA) at 5% α level of significance. Results reveal contamination of soil with Al, Cd, Fe, Pb and THC at P<0.05. The groundwater also is polluted with presumptive coliform of 1.0 x 102 to 1.5 x 103 cfu/ml-1 and heavy metals; Al, Cd, and Pb at P<0.01 indicating high significant difference. This indicates that the once protective moat is now a likely area of phytotoxicity and general environmental toxicity to man if chronic exposure is allowed by continual waste disposal. Key words: Wastes disposal soil and groundwater contamination in Benin West-Moat, case of environmental toxicity.