Runoff Modeling in Ungauged Catchments Using Machine Learning Algorithm-Based Model Parameters Regionalization Methodology

Model parameters estimation is a pivotal issue for runoff modeling in ungauged catchments.The nonlinear relationship between model parameters and catchment descriptors is a major obstacle for parameter regionalization,which is the most widely used approach.Runoff modeling was studied in 38 catchments located in the Yellow–Huai–Hai River Basin(YHHRB).The values of the Nash–Sutcliffe efficiency coefficient(NSE),coefficient of determination(R2),and percent bias(PBIAS)indicated the acceptable performance of the soil and water assessment tool(SWAT)model in the YHHRB.Nine descriptors belonging to the categories of climate,soil,vegetation,and topography were used to express the catchment characteristics related to the hydrological processes.The quantitative relationships between the parameters of the SWAT model and the catchment descriptors were analyzed by six regression-based models,including linear regression(LR)equations,support vector regression(SVR),random forest(RF),k-nearest neighbor(kNN),decision tree(DT),and radial basis function(RBF).Each of the 38 catchments was assumed to be an ungauged catchment in turn.Then,the parameters in each target catchment were estimated by the constructed regression models based on the remaining 37 donor catchments.Furthermore,the similaritybased regionalization scheme was used for comparison with the regression-based approach.The results indicated that the runoff with the highest accuracy was modeled by the SVR-based scheme in ungauged catchments.Compared with the traditional LR-based approach,the accuracy of the runoff modeling in ungauged catchments was improved by the machine learning algorithms because of the outstanding capability to deal with nonlinear relationships.The performances of different approaches were similar in humid regions,while the advantages of the machine learning techniques were more evident in arid regions.When the study area contained nested catchments,the best result was calculated with the similarity-based parameter regionalization scheme because of the high catchment density and short spatial distance.The new findings could improve flood forecasting and water resources planning in regions that lack observed data.

Soil erosion differences in paired grassland and forestland catchments on the Chinese Loess Plateau

In this study,two adjacent gauged catchments on the Chinese Loess Plateau were selected,in which one catchment was afforested and one was restored with natural vegetation in 1954.The distributions of soil erosion rates were estimated between 2010 and 2020 with a high spatial resolution of 2 m in the paired catchments based on the Revised Universal Soil Loss Equation model(RUSLE)and Geographic Information Systems(GIS).The results showed that the simulated soil erosion rates in 2010-2020 averaged 12.58 and 8.56 t ha^(-1)a^(-1)for the grassland and forestland catchment,respectively.Moreover,areas with high soil erosion rates(>80t ha^(-1)a^(-1))were mainly distributed in the topography with steep slope gradients(>45°).Comparisons between simulated soil erosion rates and observed annual sediment loads indicated that the simulation results of the grassland catchment were lower than the observed values,while it was reversed in the forestland catchment.We conclude that the RUSLE model cannot simulate the gravity erosion induced by extreme rainfall events.For the forestland catchment,insufficient streamflow and dense vegetation coverage are crucial factors resulting in hindering the movement of sediments.

Comparison of water quality in two catchments with different forest types in the headwater region of the Hun River, Northeast China

In the headwater catchments of the Hun River,Northeast China, secondary forests(SF) have been replaced by plantations since the 1960 s. Concern has been growing over this loss and the decline in water quality caused by the plantations. To test the effects of plantations on water quality, we selected two separate catchments covered by SF and Pinus koraiensis plantations(KP) to monitor physical and chemical properties of various hydrological variables including throughfall, stemflow,through-litterfall and runoff(flowing out of outlets of the catchments). The physical properties of water declined after water flowed through the two catchments as compared with rainwater. The pH of runoff in both catchments also dramatically decreased. The concentrations of Cl^-, NO_3^- and NH_4^+ in the runoff from the two catchments were similar(concentrations of Cl-and NH_4^+ in both catchments were similar to those in rainwater). Total P concentration in runoff of the SF catchment was higher than that of the KP catchment(P concentrations in both catchments were also higher than in rainwater) because P concentrations in litter and soil of the SF catchment were higher than those in the KP catchment. In summary, the rainwater became acidic in both catchments, but the responses of most water quality variables were similar in the two catchments, suggesting that appropriate ratios of KP in SF are feasible for secondary forest recovery and for preserving water quality(KP did not cause a decline in quality) in the headstream regions in Northeast of China.

Regional Design Storm and Flood Modelling—Risk Implications in Ungauged Catchments

Most planned developments in a catchment for control of excess water using a culvert, bridge or dam spillway are located at a site in a stream where there are no discharge measurements. Even though, for gauged catchments a number of established flood frequency models and rainfall-runoff models do exist, for ungauged catchments mostly regional flood frequency and event-based rainfall-runoff models are used, which depend on regional parameters. In this paper, a regional approach for design floods is presented and risk implication for design of drainage structures assessed. A case study in light of the above has been considered at four ungauged sites in the Limpopo Drainage Basin in north-eastern Botswana.

Hydrological functioning of forested catchments,Central Himalayan Region,India

Background:Central Himalayan forested catchments provide fresh water supply and innumerable ecosystem services to millions of people.Hence,the understanding of linkages between forests and water is very crucial for availability and quality of water at catchment scale.Therefore,the present study aims to understand the hydrological response of two forested catchments(namely,Arnigad and Bansigad)in the Central Himalayan Region.Methods:Threeyears’data(March,2008 to February,2011)were collected from meteorological and hydrological stations in Arnigad and Bansigad catchments.The present paper describes the mean hydrological response of these forested catchments investigated through detailed field investigation.Results:The annual hyetograph analysis revealed that the rainfall at both the catchments was highly seasonal,and wetperiod(June–September)plays a key role in catchment functioning.Exceedance of rainfall threshold of^200 mm(~10%of annual rainfall)significantly increased streamflow generation in both catchments.In Arnigad,the stream was perennial with a mean baseflow of^83mm per month(~6%of annual baseflow)whereas,Bansigad had greater seasonality due to lack of streamflow during the prewetperiod(March–May).Separation of hydrographs in Arnigad and Bansigad catchments i.e.stormflow(6%and 31%,respectively)and baseflow(50%and 32%,respectively)helped to understand the probability of flooding during wetperiod and drought during dryperiod.The forest ecosystem in Arnigad displayed healthier hydrological functioning in terms of reduced stormflow(82%),and enhanced baseflow(52%),soil moisture(13%),steady infiltration rate(22%)and lag time(~15 min)relative to Bansigad.These enhanced values indicated soil capability to store water in the forested catchment(Arnigad)and helped to understand the volume of water(discharge)that was available during dryperiod.The lower denudation rate at Arnigad by 41%resulted in decreased suspended sediment(18%)and bed load(75%)compared to Bansigad.Further,the enhanced dissolved solids in the Arnigad stream resulted from the higher organic matter generated in the forest floor.Conclusion:This study shows that rainfall during the wetperiod was the main driver of hydrological functioning,whereas,forests provided substantial services by regulating water balance,soil moisture and sediment budget through different mechanisms of forest components at catchmentscale in the Central Himalayan Region.

Hydrological Controls on Nutrient Exportation from Old-Growth Evergreen Rainforests and <i>Eucalyptus nitens</i>Plantation in Headwater Catchments at Southern Chile

Soil cover disturbances have a direct effect on biogeochemistry, potentially enhancing nutrient loss, land degradation and associated changes in ecosystem services and livelihood support. The objective of this study was to assess how canopy affected throughfall chemistry and how hydrology affected stream nutrient load responses in two watersheds dominated by native old-growth evergreen rainforest (NF) and exotic plantation of Eucalyptus nitens (EP), located at the Coastal mountain range of southern Chile (40&deg;S). We measured nitrogen (NO3-N, NH4-N, Organic-N, Total-N) and total phosphorus (Total-P) at catchment discharge, and δ18O in throughfall precipitation and stream discharge in both catchments, in order to separate throughfall (or new water) contributions during storm events. It was hypothesized that all nutrients showed an increase in concentration as discharge increased (or enhanced hydrological access), in EP;but not in NF. Our results indicated that Organic-N, Total-N and Total-P concentrations were positively related to discharge. However, NO3<sup style="margin-left:-7px;">--N showed a negative correlation with catchment discharge. Organic-N and Total-P showed a flush during storm events;the opposite was observed for NO3<sup style="margin-left:-7px;">--N. However, this behavior suggested that NO3<sup style="margin-left:-7px;">--N was being retained by charged particles or soil micro biota, whether Organic-N was flushed as it was more concentrated in big pore water that was not tightly attached, compared with NO3<sup style="margin-left:-7px;">--N.

Large Wood Volume and Longitudinal Distribution in Channel Segments Draining Catchments with Different Land Use, Chile

The storage, longitudinal distribution and recruitment processes of in-stream large wood (LW) were studied comparing channel segments draining four Chilean mountain catchments with different land use. The segments were divided into relatively uniform reaches of different lengths and surveyed for LW (piece dimensions, position in the channel, orientation to flow and aggregation) and stream morphology (slope and bank full channel width and depth) characterizations. LW volume stored in the Pichun, El Toro and Vuelta de Zorra study channels are within the range informed in international researches from streams draining catchments with similar forest covers. However, the 1057 m3/ha of LW stored in Tres Arroyos is extremely high and in the same order of magnitude than the reports from old-growth forests in the Pacific Northwest of USA. The size of the area that can potentially provide wood to streams depends on the wood supply mechanisms within any catchment, and the LW stored in the study segments increases as the size of this area increases. This study aims to contribute to the knowledge on the effects of LW in mountain channels, gathering new information and expanding investigations developed in Chile since 2008. This research was carried out within the framework of Project FONDECYT 11106209.

Episode Studies on Catchments Chemistry at Tie Shan Ping,Chongqing

The Tie Shan Ping(TSP) catchments are acidified due to acid deposition.The highest concentrations of SO2-4,NO-3,Ca2+,Mg2+ Al3+ and H+ occur in soil water and the maximum of molar ratio Ali/(Ca+Mg) during the Episode Studies is 1.27 in the bottom soil water in May 2003.Fuzzy Cluster Analysis for compartmental water chemistry in catchments shows stream water(SW) originates from the soil water generally.During event rain there may be 'pulse' of high concentration of chemical species in the stream.Total organic carbon,organic bound aluminum,total phosphorus,total nitrogen,NO-3 in SW are controlled by quick(high) flow.SW at new dam at TSP is from quick flow largely,including overland flow during wet period.Al3+,SO2-4 and H+ in SW are controlled by base flow during dry period and SW at old dam at TSP is from the base flow,largely.There are "alkaline pulse" and "acid pulse" in stream water during the event rain.The former may be caused by overland flow over the litterfall and topsoil horizons,and the latter by "piston flow" from soil water in deeper soil horizon largely.

Using Artificial Neural Network to Estimate Sediment Load in Ungauged Catchments of the Tonle Sap River Basin, Cambodia

Concern on alteration of sediment natural flow caused by developments of water resources system, has been addressed in many river basins around the world especially in developing and remote regions where sediment data are poorly gauged or ungauged. Since suspended sediment load (SSL) is predominant, the objectives of this research are to: 1) simulate monthly average SSL (SSLm) of four catchments using artificial neural network (ANN);2) assess the application of the calibrated ANN (Cal-ANN) models in three ungauged catchment representatives (UCR) before using them to predict SSLm of three actual ungauged catchments (AUC) in the Tonle Sap River Basin;and 3) estimate annual SSL (SSLA) of each AUC for the case of with and without dam-reservoirs. The model performance for total load (SSLT) prediction was also investigated because it is important for dam-reservoir management. For model simulation, ANN yielded very satisfactory results with determination coefficient (R2) ranging from 0.81 to 0.94 in calibration stage and 0.63 to 0.87 in validation stage. The Cal-ANN models also performed well in UCRs with R2 ranging from 0.59 to 0.64. From the result of this study, one can estimate SSLm and SSLT of ungauged catchments with an accuracy of 0.61 in term of R2 and 34.06% in term of absolute percentage bias, respectively. SSLA of the AUCs was found between 159,281 and 723,580 t/year. In combination with Brune’s method, the impact of dam-reservoirs could reduce SSLA between 47% and 68%. This result is key information for sustainable development of such infrastructures.

Slope-gully erosion relationship in small catchments of the middle reaches of the Yellow River

The slope-gully erosion relationship in small catchments of the middle reaches of the Yellow River has long been a topic concerned by relevant departments in China Slope-gully relationship in typical small catchment is determined determined on the concept of net increase of sediment yield by using analytical method of sediment formation at different positions in the catchment The result shows that sediments in a small catchment in the middle reaches of the Yellow River mainly come from slopes. ms paper indicated that the sediment sources from slopes are roughly 55, 60, 78 and 85 % of the total sediment yield of a small catchment in Yangdaogou. Wangjiagou. Jiuyuangou and Nanxiaohegou, respectively, due to impacts of varying degress from slope runoff.

Assessing discharge periodicity in mountain catchments using classified environmental conditions(Tatra Mountains, Poland)

The periodicity of a river expressed in cycles of various lengths(monthly, seasonal,multiannual) is a result of climatic factors and overlapping environmental conditions within its catchment. In uncontrolled or poorly surveyed catchments, it is very difficult to determine the duration of a stream’s hydrological activity. This is especially relevant for catchments with complicated water circulation in karstic rocks. The present study concerns the small catchment of the Str??yski Potok river located in the area of the Tatra National Park, in the Western Tatras. The observation period covered the 2015 hydrological year, which differed hydrologically from average conditions. This study aims to develop a simple method to explain the processes shaping the mountain stream discharge periodicity. The research employed periodic field observations linked with climatic and non-climatic factors. Environmental conditions were assessed as four classes reflecting their influence on appearance or disappearance of mountain stream water. Class boundaries were the values of quartiles. The degree of correspondence between environmental factors and stream field observations was described via the Index DC(Degree Correspondence Index) approach.Complete correspondence(Index DC =0) was found in 23% catchments, a weak relationship between conditions favouring discharge and actual condition(Index DC=-1, +1) was noted within 11 catchments,while in 9 catchments, no such relationship was found(Index DC =-2, +2). The obtained results indicate a correspondence or lack thereof between the environmental potential of the catchment and its discharge periodicity. The discrepancies between the assessment of the influence of climatic and nonclimatic factors and the data collected during field observations provide a basis for more detailed studies.Continuation of these studies based on the proposed classifications will allow for a more complete explanation of water disappearance in river channels and the determination of their short-and long-term discharge periodicity.

Winter Rain versus Snow in Headwater Catchments: Responses of an Unconfined Pumice Aquifer, South-Central Oregon, USA

Winter precipitation in two headwaters catchments (elevation ~1600 m) in the rain shadow of the Cascades volcanic arc in south-central Oregon normally falls as snow. However, in water year 2015, winter precipitation fell mainly as rain. An eight year study of the unconfined pumice aquifer allowed inter-annual comparison of groundwater recharge during the freshet and discharge during the growing season. During these water years precipitation ranged from 67% (WY2014) to 132% (WY2017) of the 30 year average, and included the rain dominated winter of WY2015 when precipitation during the water year was 98% of the 30 year average. Change in storage in the pumice aquifer was estimated from thickness of the pumice deposit and depth to water table from the ground surface. Measurements were made where 1) the pumice aquifer was exposed at the surface;2) where the aquifer was partially eroded and overlain by either alluvium or lacustrine glassy silt to fine sand;3) fens where the partially eroded aquifer was overlain by peat;and 4) monitoring wells drilled through the pumice aquifer into bedrock. In all settings, groundwater storage in the pumice aquifer following the rain-dominated winter of WY2015 was similar or less than storage following the drought of WY2014 when winter precipitation fell as snow. Storage at the end of WY2014 and WY2015 was the least observed in the eight year study. Winter-time rain during WY2015 produced runoff rather than storage in snow pack. Runoff conveyed from the catchments by flow in stream reaches normally dry from late summer through the winter months. Rain-dominated winter precipitation stresses the perched pumice aquifer. Winter storms starting as rain and turning late to snow and ground-freezing temperatures lead to runoff during the next rain-dominated precipitation event. These patterns produced stream flow in channels that are commonly dry during the winter, reduced near-surface groundwater storage in the pumice aquifer, muted springtime freshet, and stressing of groundwater-dependent ecosystems, forage in meadows, and forest health.

Assessment of debris flow magnitude in small catchments of the lombardy alps: the val gola case study

Debris flows are among the most destructive of all water-related disasters. They mainly affect mountain areas in a wide range of morpho- climatic environments. Therefore, accurate pre-diction of their run out distances, magnitudes and velocities plays a role of paramount impor-tance, in order to plan and design appropriate structural and non-structural defence measures. In this context, a number of Authors have de-veloped methods feasible to evaluate the ten-dency of a catchment to generate debris flow, without giving an estimation of the magnitude. Other empirical procedures are based on the analysis of historical series of debris flow, oc-curred in similar environments, to assess the relationship between the catchment character-istics and the maximum movable debris vol-umes. In this paper, and with reference to Val Gola—a small catchment in the North-East Lom- bardy where debris flows frequently occur—a number of methods, belonging to each of the above mentioned categories, have been briefly reviewed and applied in order to evaluate their effectiveness and consistency.

Assessing Water Availability and Unmet Water Demand Using the WEAP Model in the Semi-Arid Bweengwa, Kasaka and Magoye Sub-Catchments of Southern Zambia

Located in the semi-arid zone of Zambia, the Mutama-Bweengwa, Kasaka and Magoye sub-catchments have witnessed a high demand for water due to increase in population and socio-economic activities putting more pressure on water resources. This study assesses the hydrological components and ascertains the available water resources and unmet demand in the sub-catchments using the Water Evaluation And Planning (WEAP) Model and hydrometeorological data collected between 1951 and 2018. The model was calibrated and validated on 1971-1981 and 2008-2018 data respectively. The results reveal that the sub-catchments have transitioned from positive to negative water balance with -164.295 Mm3/year for Mutama-Bweengwa, -19.021 Mm3/year for Kasaka and -86.368 Mm3/year for Magoye. Evaporation was 1815.259 Mm3/year for Mutama-Bweengwa, 1162.655 Mm3/year for Kasaka and 1505.664 Mm3/year for Magoye. The demand for water has been increasing over time for various purposes such as irrigation, domestic, urban/rural water supply and livestock. The overall water storage in the sub-catchments showed a negative water balance for the year 2018. The observed and simulated peak streamflow were 8.16 m3/s and 7.7 m3/s occurring during the month of January and February respectively. The WEAP model performance achieved R2 of 0.98 during calibration and 0.95 for validation, and an NSE of 0.83 for calibration and 0.85 during validation. The values of objective functions show that the hydrology of the Mutama-Bweengwa, Kasaka and Magoye sub-catchments as predicted by the WEAP model provides satisfactory confidence for prediction of future streamflow and hence projection based on future scenarios.

Temporal Dynamics of Land Use and Water Quality in Three Sub-Catchments of the Rur River, Germany

The Rur catchment has over time undergone land use change which could have affected the biogeochemical processes of the river. Three sub-catchments in the Rur, Upper Rur, Inde and Wurm have different kinds of land use. Upper Rur is more natural catchment;Inde is mixed type and Wurm is highly modified by anthropogenic activities. This study investigated how land use changes from 2000 to 2018 have influenced SO4 and Cl dynamics in the Rur catchment. Land use maps were developed in QGIS environment for land use change calculation. Historical water quality data were collected from the online public source by Ministry of Environment and Nature Conservation in Germany. R-software was used for statistical analysis and graphical presentation. Less land use change was observed in the Upper Rur between 2000 to 2018. But in the Inde and Wurm decrease in agricultural land and associated increase in industrial, commercial and urban land were observed. Increase in mining area inside the catchment has enhanced the level of SO4 and EC in the Inde river. Conversion rates of natural to human dominated land use could be quantified in this study through land use change mapping, which will further help in making water management plan for these and comparable German and European catchments. However, high quality historical data set is a key requirement to maximize the output in process of relating impact of land use change in water quality.

MINErosion 4:Using measurements from a tilting flume-rainfall simulator facility to predict erosion rates from post-mining catchments/landscapes in Central Queensland,Australia

The use of draglines to remove overburden in Queensland opencut mines,results in landscapes that consist of long parallel tertiary overburden spoil-piles that are generally highly saline,dispersive,and highly erodible.The height of these spoil-piles may exceed 50-60 m above the original landscapes and the slopes are at the angle of repose of around 75%or 37°.Legislation and public opinion require that these highly disturbed open-cut post-mining landscapes should be satisfactorily rehabilitated into an approved post-mining land use with acceptable erosion rates.Therefore,these slopes must be reduced before the landscape can be rehabilitated.The most expensive component of the rehabilitation process is the re-shaping and preparation of the overburden to create a suitable landscape for vegetation growth.As soils and overburden varies greatly in their erodibilities,the extent and cost of earthworks can be minimized,and rehabilitation failures avoided,if soil erosion from designed landscapes can be predicted using laboratory-based parameters prior to construction of these landscapes.This paper describes the development of a model for that purpose.A catchment or landscape erosion model MINErosion 4 was developed by upscaling the existing hillslope model MINErosion 3(So,et al.,2018)and integrate it with both ESRI ArcGIS 10.3 or QGIS 3.16(freeware),to predict event based and mean annual erosion rate from a postmining catchment or landscape.MINErosion 3 is a model that can be used to predict event and annual erosion rates from field scale hillslopes using laboratory measured erodibility parameters or routinely measured soil physical and chemical properties,and to derive suitable landscape design parameters(slope gradient,slope length and vegetation cover)that will result in acceptable erosion rates.But it cannot be used to predict the sediment delivery from catchments or landscapes.MINErosion 4 was validated against data collected on three instrumented catchments(up to 0.91 ha in size)on the Curragh mine site in Central Queensland.The agreement between predicted(Y)and measured(x)values were very good with the regression equation of Y-0.92X and an R^(2) value of 0.81 for individual storm events,and Y-1.47X and an R^(2) value of 0.73 for the average annual soil loss.This is probably the first time that a catchment scale erosion is successfully predicted from laboratory measured erodibility parameters.

Role of rural solid waste management in non-point source pollution control of Dianchi Lake catchments, China

In recent years,with control of the main muni-cipal and industrial point pollution sources and imple-mentation of cleaning for some inner pollution sources in the water body,the discharge of point source pollution decreased gradually,while non-point source pollution has become increasingly distressing in Dianchi Lake catch-ments.As one of the major targets in non-point source pollution control,an integrated solid waste controlling strategy combined with a technological solution and man-agement system was proposed and implemented based on the waste disposal situation and characteristics of rural solid waste in the demonstration area.As the key techno-logy in rural solid waste treatment,both centralized plant-scale composting and a dispersed farmer-operated waste treating system showed promise in rendering timely ben-efits in efficiency,large handling capacity,high quality of the end product,as well as good economic return.Problems encountered during multi-substrates co-com-posting such as pathogens,high moisture content,asyn-chronism in the decomposition of different substrates,and low quality of the end product can all be tackled.92.5% of solid waste was collected in the demonstration area,while the treating and recycling ratio reached 87.9%,which pre-vented 32.2 t nitrogen and 3.9 t phosphorus per year from entering the water body of Dianchi Lake after imple-mentation of the project.

Enhancing Geological Understanding and Identifying Gold Anomalies in the Ailaoshan Orogen

The Ailaoshan Orogen in the southeastern Tibet Plateau,situated between the Yangtze and Simao blocks,underwent a complex structural,magmatic,and metamorphic evolution resulting in different tectonic subzones with varying structural lineaments and elemental concentrations.These elements can conceal or reduce anomalies due to the mutual effect between different anomaly areas.Dividing the whole zone into subzones based on tectonic settings,ore cluster areas,or sample catchment basins(Scb),geochemical and structural anomalies associated with gold(Au)mineralization have been identified utilizing mean plus twice standard deviations(Mean+2STD),factor analysis(FA),concentration-area(CA)modeling of stream sediment geochemical data,and lineament density in both the Ailaoshan Orogen and the individual subzones.The FA in the divided 98 Scbs with 6 Scbs containing Au deposits can roughly ascertain unknown rock types,identify specific element associations of known rocks and discern the porphyry or skarn-type Au mineralization.Compared with methods of Mean+2STD and C-A model of data in the whole orogen,which mistake the anomalies as background or act the background as anomalies,the combined methods of FA and C-A in the separate subzones or Scbs works well in regional metallogenic potential analysis.Mapping of lineament densities with a 10-km circle diameter is not suitable to locate Au deposits because of the delineated large areas of medium-high lineament density.In contrast,the use of circle diameters of 1.3 km or 1.7 km in the ore cluster scale delineates areas with a higher concentration of lineament density,consistent with the locations of known Au deposits.By analyzing the map of faults and Au anomalies,two potential prospecting targets,Scbs 1 and 63 with a sandstone as a potential host rock for Au,have been identified in the Ailaoshan Orogen.The use of combined methods in the divided subzones proved to be more effective in improving geological understanding and identifying mineralization anomalies associated with Au,rather than analyzing the entire large area.

Modelling Land Use/Land Cover Change of River Rwizi Catchment, South-Western Uganda Using GIS and Markov Chain Model

Analysis of catchment Land use/Land cover (LULC) change is a vital tool in ensuring sustainable catchment management. The study analyzed land use/land cover changes in the Rwizi catchment, south western Uganda from 1989-2019 and projected the trend by 2040. Landsat images, field observations, key informant interviews and focus group discussions were used to collect data. Changes in cropland, forestland, built up area, grazing land, wetland and open water bodies were analyzed in ArcGIS version 10.2.2 and ERDAS IMAGINE 14 software and a Markov chain model. All the LULC classes increased in area except grazing land. Forest land and builtup area between 2009-2019 increased by 370.03% and 229.53% respectively. Projections revealed an increase in forest land and builtup area by 2030 and only built up area by 2040. LULCC in the catchment results from population pressure, reduced soil fertility and high value of agricultural products.

A New Algorithm to Automatically Extract the Drainage Networks and Catchments Based on Triangulation Irregular Network Digital Elevation Model

A new algorithm to automatically extract drainage networks and catchments based on triangulation irregular networks(TINs) digital elevation model(DEM) was developed. The flow direction in this approach is determined by computing the spatial gradient of triangle and triangle edges. Outflow edge was defined by comparing the contribution area that is separated by the steepest descent of the triangle. Local channels were then tracked to build drainage networks. Both triangle edges and facets were considered to construct flow path. The algorithm has been tested in the site for Hawaiian Island of Kaho'olawe, and the results were compared with those calculated by ARCGIS as well as terrain map. The reported algorithm has been proved to be a reliable approach with high efficiency to generate well-connected and coherent drainage networks.