Establishing the link between urban land cover change and the proliferation of aquatic hyacinth (Eichhornia crassipes) in Harare Metropolitan, Zimbabwe

Urbangrowthisakeyprocessaffectingthefunctioningofnaturalecosystems,andconsequentlythegloballand-surface process. This work aimed at establishing the link between land cover changes around HarareMetropolitancityandtheproliferationofaquatichyacinth(Eichhornia crassipes)inLakeChivero.RemotelysensedLandsatseriesacquiredintheyear1973,1981,1994,1998,2008,2009and2014wasused.Imageclassificationwasimplementedtomaptheassociatedchangesovertimeusingdiscriminantanalysisalgorithm.Derivedthematiclandcovermapsshowedthatagriculturallandincreasedfrom2%in1973toa5%in1981reachingupto30%in2014,whereasthecity'slandareasignificantly(p<0.05)increasedbetween1973and1994.However,waterhyacinthconstantlyincreasedovertime.ThespatialandtemporalresolutionofLandsatimagesdetectedlandcoverchangesandtheproliferationofaquatichyacinth(Eichhorniacrassipes)intheLakeChiveroovertime

The physic-chemical assessment of urban river basin using macroinvertebrate indices for the environmental monitoring of urban streams

BACKGROUND AND OBJECTIVES: The major sources of pollution along the Mukuvisi River are industrial effluents from Msasa, Graniteside, and Southerton industrial sites, sewage effluent from Firle sewage works, pesticide and fertilizer runoff from Pension and surrounding farms, and domestic and diffuse pollution from residential areas. The primary objective of this study was to assess the impact of point and non-point pollution sources on macroinvertebrates variability and investigate the seasonal water quality deterioration along the Mukuvisi River. To evaluate macroinvertebrate community diversity using South African Scoring System 5 protocol for rapid bioassessment of water quality. The combined application of benthic macroinvertebrates and physic-chemical parameters was the focus of this research to validate the water quality status of the urban River systems concerning emerging pollutants in urban areas.METHODS: According to the Harare municipality pollution control strategy and surveillance, only twelve accessible sampling points were chosen along the river. Macroinvertebrate samples and physic-chemical measurements were collected once or twice a month, according to the city of Harare’s sampling schedule. The ancillary information, temperature, pH, and conductivity were measured on-site with a mercury bulb thermometer, a pH meter, and a conductivity meter, respectively. The standard South African Scoring System 5 sampling protocol was used for the sampling and identification of the macroinvertebrates community.FINDINGS: The early assessments showed that water pollution was, in the 1st place and as a primary issue, a biological matter, and its primary effects could have been traced to living organisms. Eutrophication in Manyame catchment, Harare, Zimbabwe is subjected to prolonged and cumulative ecosystem stress because of human activities, sewage disposal, and industrial discharges, among other pollution sources. The Phosphorus-P, Biological Oxygen Demand, Chemical Oxygen Demand, and Ammonia-NH3 (from 0, 6.9, 118, and 0 to 3.8, 81.9, 840, and 31 mg/L respectively) concentration increases downstream in both seasons. The Dissolved Oxygen saturation was 75% and 67% upstream in the dry-and-wet season and was reduced to 0% downstream in both seasons. The evaluation of macroinvertebrate diversity provided evidence that Mukuvisi River water was polluted based on the South African Scoring System, especially in the dry season.CONCLUSIONS: The physic-chemical parameters were significantly related to macroinvertebrates diversity. In the assessment of river water quality, both macroinvertebrate indices and physio-chemical parameters can be sampled together to avoid bias. The results indicated that human activities from the upstream were inducing water pollution. Industries need to adhere to the wastewater discharge guidelines

Efeitos da arborização urbana na redução do escoamento pluvial superficial e no atraso do pico de vazão

Soil proofng and absence of tree cover produces more volume of surface runoff, enlarges the peak flow and reduces the delay time. The search for alternatives to reduce the volume of surface runoff in urban areas is important to get the hydrological answers to the problems caused by the urbanization process and, along with that, to reduce the risk of flooding. This article proposes to estimate the reduction of runoff and the delay in the peak flow caused by the presence of three species of trees (Mangifera indica, Tabebuia ochracea and Licania tomentosa) in urban areas. This allowed the quantifcation and the performance analysis of tree species in reducing urban runoff; the arboreal parameters correlated with the flow capacity reduction; and examined whether there is reduction and delay in the peak flows. The benefts from the interception of storm water for trees need to be pondered and guaranteed in afforestation master plans and urban drainage in order to reach the mitigation of damage caused by the neglect of urban water. For this, level sensors were used (limnigraphs) to quantify the surface runoff in areas with and without the presence of arboreal coverage, and in experimental structures set on waterproof, semipermeable and permeable soil. For events with an average value of gross precipitation of 17.1 mm, the presence of arboreal individuals caused an average time delay up to the peak flow of 3 minutes, an average reduction of peak flow of 0.8 mm/min and it contributed to an average reduction of surface runoff of 4.7 mm/min.A impermeabilização do solo e ausência de cobertura arbórea produz maior volume de escoamento superficial, amplia o pico de vazão e reduz o tempo de retardo. A busca por alternativas para diminuição do volume de escoamento superficial em áreas urbanas é importante para obter respostas hidrológicas aos problemas ocasionados pelo processo de urbanização e, com isso, amenizar o risco de inundação. Este estudo se propôs a estimar a redução do escoamento superficial e o atraso no pico de vazão ocasionados pela presença das árvores de três espécies (Mangifera indica, Tabebuia ochracea e Licania tomentosa) no meio urbano, o que permitiu a quantificação e análise do desempenho de espécies arbóreas na redução do escoamento urbano; correlacionou os parâmetros arbóreos com a capacidade de redução do escoamento; bem como averiguou se há redução e atraso nos picos de vazão. Os benefícios provenientes da interceptação das águas pluviais pelas árvores precisam ser ponderados e garantidos nos planos diretores de arborização e de drenagem urbana, de modo a alcançar a mitigação dos prejuízos provocados pelo descaso com as águas urbanas. Para isso, foram utilizados sensores de nível (linígrafos) para a quantificação do escoamento superficial em áreas com e sem a presença da cobertura arbórea, e em estruturas experimentais instaladas sobre solo impermeabilizado, semipermeável e permeável. Em eventos cujo valor mediano de precipitação bruta foi de 17.1 mm, a presença dos indivíduos arbóreos ocasionou um atraso mediano no tempo ao pico de vazão de 3 minutos, uma redução do pico de vazão de 0.8 mm/min e do escoamento superficial de 4.7 mm/min

Efeitos da arborização urbana na redução do escoamento pluvial superficial e no atraso do pico de vazão

Soil proofng and absence of tree cover produces more volume of surface runoff, enlarges the peak flow and reduces the delay time. The search for alternatives to reduce the volume of surface runoff in urban areas is important to get the hydrological answers to the problems caused by the urbanization process and, along with that, to reduce the risk of flooding. This article proposes to estimate the reduction of runoff and the delay in the peak flow caused by the presence of three species of trees (Mangifera indica, Tabebuia ochracea and Licania tomentosa) in urban areas. This allowed the quantifcation and the performance analysis of tree species in reducing urban runoff; the arboreal parameters correlated with the flow capacity reduction; and examined whether there is reduction and delay in the peak flows. The benefts from the interception of storm water for trees need to be pondered and guaranteed in afforestation master plans and urban drainage in order to reach the mitigation of damage caused by the neglect of urban water. For this, level sensors were used (limnigraphs) to quantify the surface runoff in areas with and without the presence of arboreal coverage, and in experimental structures set on waterproof, semipermeable and permeable soil. For events with an average value of gross precipitation of 17.1 mm, the presence of arboreal individuals caused an average time delay up to the peak flow of 3 minutes, an average reduction of peak flow of 0.8 mm/min and it contributed to an average reduction of surface runoff of 4.7 mm/min.A impermeabilização do solo e ausência de cobertura arbórea produz maior volume de escoamento superficial, amplia o pico de vazão e reduz o tempo de retardo. A busca por alternativas para diminuição do volume de escoamento superficial em áreas urbanas é importante para obter respostas hidrológicas aos problemas ocasionados pelo processo de urbanização e, com isso, amenizar o risco de inundação. Este estudo se propôs a estimar a redução do escoamento superficial e o atraso no pico de vazão ocasionados pela presença das árvores de três espécies (Mangifera indica, Tabebuia ochracea e Licania tomentosa) no meio urbano, o que permitiu a quantificação e análise do desempenho de espécies arbóreas na redução do escoamento urbano; correlacionou os parâmetros arbóreos com a capacidade de redução do escoamento; bem como averiguou se há redução e atraso nos picos de vazão. Os benefícios provenientes da interceptação das águas pluviais pelas árvores precisam ser ponderados e garantidos nos planos diretores de arborização e de drenagem urbana, de modo a alcançar a mitigação dos prejuízos provocados pelo descaso com as águas urbanas. Para isso, foram utilizados sensores de nível (linígrafos) para a quantificação do escoamento superficial em áreas com e sem a presença da cobertura arbórea, e em estruturas experimentais instaladas sobre solo impermeabilizado, semipermeável e permeável. Em eventos cujo valor mediano de precipitação bruta foi de 17.1 mm, a presença dos indivíduos arbóreos ocasionou um atraso mediano no tempo ao pico de vazão de 3 minutos, uma redução do pico de vazão de 0.8 mm/min e do escoamento superficial de 4.7 mm/min

Hydrological Impacts of Urbanization of Two Catchments in Harare, Zimbabwe

By increased rural-urban migration in many African countries, the assessment of changes in catchment hydrologic responses due to urbanization is critical for water resource planning and management. This paper assesses hydrological impacts of urbanization on two medium-sized Zimbabwean catchments (Mukuvisi and Marimba) for which changes in land cover by urbanization were determined through Landsat Thematic Mapper (TM) images for the years 1986, 1994 and 2008. Impact assessments were done through hydrological modeling by a topographically driven rainfall-runoff model (TOPMODEL). A satellite remote sensing based ASTER 30 metre Digital Elevation Model (DEM) was used to compute the Topographic Index distribution, which is a key input to the model. Results of land cover classification indicated that urban areas increased by more than 600 % in the Mukuvisi catchment and by more than 200 % in the Marimba catchment between 1986 and 2008. Woodlands decreased by more than 40% with a greater decrease in Marimba than Mukuvisi catchment. Simulations using TOPMODEL in Marimba and Mukuvisi catchments indicated streamflow increases of 84.8 % and 73.6 %, respectively, from 1980 to 2010. These increases coincided with decreases in woodlands and increases in urban areas for the same period. The use of satellite remote sensing data to observe urbanization trends in semi-arid catchments and to represent catchment land surface characteristics proved to be effective for rainfall-runoff modeling. Findings of this study are of relevance for many African cities, which are experiencing rapid urbanization but often lack planning and design

Hydrological impacts of urbanization of two catchments in Harare, Zimbabwe

By increased rural-urban migration in many African countries, the assessment of changes in catchment hydrologic responses due to urbanization is critical for water resource planning and management. This paper assesses hydrological impacts of urbanization on two medium-sized Zimbabwean catchments (Mukuvisi and Marimba) for which changes in land cover by urbanization were determined through Landsat Thematic Mapper (TM) images for the years 1986, 1994 and 2008. Impact assessments were done through hydrological modeling by a topographically driven rainfall-runoff model (TOPMODEL). A satellite remote sensing based ASTER 30 metre Digital Elevation Model (DEM) was used to compute the Topographic Index distribution, which is a key input to the model. Results of land cover classification indicated that urban areas increased by more than 600 % in the Mukuvisi catchment and by more than 200 % in the Marimba catchment between 1986 and 2008. Woodlands decreased by more than 40% with a greater decrease in Marimba than Mukuvisi catchment. Simulations using TOPMODEL in Marimba and Mukuvisi catchments indicated streamflow increases of 84.8 % and 73.6 %, respectively, from 1980 to 2010. These increases coincided with decreases in woodlands and increases in urban areas for the same period. The use of satellite remote sensing data to observe urbanization trends in semi-arid catchments and to represent catchment land surface characteristics proved to be effective for rainfall-runoff modeling. Findings of this study are of relevance for many African cities, which are experiencing rapid urbanization but often lack planning and design

Hydrological Impacts of Urbanization of Two Catchments in Harare, Zimbabwe

By increased rural-urban migration in many African countries, the assessment of changes in catchment hydrologic responses due to urbanization is critical for water resource planning and management. This paper assesses hydrological impacts of urbanization on two medium-sized Zimbabwean catchments (Mukuvisi and Marimba) for which changes in land cover by urbanization were determined through Landsat Thematic Mapper (TM) images for the years 1986, 1994 and 2008. Impact assessments were done through hydrological modeling by a topographically driven rainfall-runoff model (TOPMODEL). A satellite remote sensing based ASTER 30 metre Digital Elevation Model (DEM) was used to compute the Topographic Index distribution, which is a key input to the model. Results of land cover classification indicated that urban areas increased by more than 600 % in the Mukuvisi catchment and by more than 200 % in the Marimba catchment between 1986 and 2008. Woodlands decreased by more than 40% with a greater decrease in Marimba than Mukuvisi catchment. Simulations using TOPMODEL in Marimba and Mukuvisi catchments indicated streamflow increases of 84.8 % and 73.6 %, respectively, from 1980 to 2010. These increases coincided with decreases in woodlands and increases in urban areas for the same period. The use of satellite remote sensing data to observe urbanization trends in semi-arid catchments and to represent catchment land surface characteristics proved to be effective for rainfall-runoff modeling. Findings of this study are of relevance for many African cities, which are experiencing rapid urbanization but often lack planning and design

Análisis de conveniencia de imágenes satelitales de acceso abierto para la determinación de coeficientes de escurrimiento

The runoff coefficient (CE) is a key variable in the study of hydrological behavior. Geomatics allows us to model land coverage change and generate thematic maps of the runoff coefficients spatial distribution. Integration and analysis of different layers of data in Geographic Information Systems (SIG) and the use of products generated by remote sensing (PR) is important for this matter. Despite the existence of a high number of PR products, a methodological basis has not yet been developed to systematically select the appropriate product to each project. In this study, we propose a comparison scheme of images to perform an analysis that yields the most convenient image in the determination of land coverage used in CE’s calculus. Sensors Landsat 8, MODIS, Sentinel-1 and Sentinel-2 were included. Characteristics of each sensor were related with the ones that define the Hydrological behavior of a basin. The analysis area was limited to three zones: Bajo Grijalva (BG) subregion, Valley of Mexico basin (VM) and San Juan river- Bajo Bravo river subregion (BB). These areas represent the different characteristic climates of Mexican territory. The terrestrial coverage of the areas was determined applying the algorithms of Minimum Distance, Spectral Angle Mapping, Maximum Likelihood and Vector Support Machines. Each of these algorithms were used in the L8, MD, S1 and S2 products obtaining different results. Total Agreement, commission and omission error was calculated for each of the classifications. Global average agreement by Basin, Sensor and Algorithm was analyzed. Average of Domain, agreement, commission and omission error by class was calculated for each basin. The temporal, spatial, spectral and radiometric resolution and its influence on the terrestrial coverage determined by each sensor-classifier combination were analyzed. In general terms, L8 and the DM algorithm presented the greatest agreement in the determination of land cover. However, watershed analysis yielded different results for each of them. In the BB area, it obtained a greater agreement with the S2-DM combination. The L8 sensor obtained the best performance in the BG area along with the MSV algorithm. The L8-MAE combination achieved the greatest agreement in the VM areas. The determination of the CE by this method has the advantage of obtaining baseline values that allow performing runoff analysis at local scales. The results showed that the selection of the image should include the characteristic resolutions of each sensor, as well as the study period, the type of land cover and its dynamics, the climate, the size of the basin and the classification algorithm usedEl coeficiente de escurrimiento (CE) es una variable clave en estudio del comportamiento hidrológico. La Geomática a través de la integración y análisis de diferentes capas de datos en los Sistemas de Información Geográfica (SIG) y el uso de los productos generados por la percepción remota (PR), nos permite modelar los cambios de cobertura terrestre y generar mapas temáticos de la distribución espacial de los CE. A pesar de a la existencia de un número elevado de productos provenientes de PR disponibles en la actualidad, aun no se ha desarrollado una base metodológica que permita seleccionar de forma sistemática el producto adecuado al proyecto en cuestión. En el presente estudio se propone un esquema de comparación de las imágenes generadas por los sensores Landsat 8, MODIS, Sentinel 1 y Sentinel 2 para realizar un análisis que arroje la imagen más conveniente en la determinación de la cobertura terrestre contemplado las características que definen el comportamiento hidrológico de la cuenca. El área de análisis se limitó a tres zonas que representan a las distintas características presentes en el territorio mexicano, estas áreas se encuentran dentro de la subregión Bajo Grijalva (BG), la cuenca del Valle de México (VM) y las cuencas del rio San juan y el rio Bajo Bravo (BB). Se determinó la cobertura terrestre de dichas áreas aplicando los algoritmos de Distancia Mínima (DM), Mapeo del Ángulo espectral (MAE), Máxima Verosimilitud (MV) y Maquinas de Soporte Vectorial (MSV). Cada uno de estos algoritmos fueron empleados en los productos L8, MD, S1 y S2 obteniendo distinto resultados. Se determinó el acuerdo, error de comisión y omisión global para cada una de las clasificaciones. Se analizó el Acuerdo global promedio por Cuenca, Sensor y Algoritmo y se calculó el dominio, acuerdo, error de comisión y omisión promedio de la clase en los resultados de todas las clasificaciones de cada cuenca. Se analizó la resolución temporal, espacial, espectral y radiométrica y su influencia en la cobertura terrestre determinada por cada combinación sensor-clasificador. De manera general el sensor L8 y el algoritmo DM presentaron el mayor acuerdo en la determinación de la cobertura terrestre. Sin embargo, el análisis de cuencas arrojó resultados distintos para cada una de ellas. En área del BB obtuvo un mayor acuerdo con la combinación S2-DM. El sensor L8 obtuvo el mejor desempeño en el área del BG junto con el algoritmo MSV. La combinación L8-MAE logró el mayor acuerdo en el área del VM. La determinación del CE por este método presenta la ventaja de obtener valores puntales que permite realizar análisis de escurrimiento en escalas locales. Los resultados mostraron que la selección de la imagen debe incluir las resoluciones características de cada sensor, así como el periodo de estudio, el tipo de cobertura terrestre y su dinámica, el clima, el tamaño de la cuenca y el algoritmo de clasificación emplead