Hydrology/Hydrography

Global hydrology modelling and uncertainty: running multiple ensembles with a campus grid

by Simon Gosling

Integrated water resource management using remote sensing and geophysical techniques: Aravali quartzite, Delhi, India

by Prashant K. Srivastava

Information on land use patterns and changes are required for planning, utilization, and implementation of groundwater... more Information on land use patterns and changes are required for planning, utilization, and implementation of groundwater exploration and rainwater harvesting. Multispectral and multitemporal satellite data has the potential to delineate sites for water resource management. Magnetic and resistivity surveys can further confirm subsurface aquifer configuration. Due to heterogeneity of aquifer materials, it is essential to take a holistic approach that includes geological information supplemented with remotely sensed data and supported by resistivity and magnetic anomaly detection. This approach is used for locations of higher spectral reflectance and lineament density which are assumed to be areas of aquifer recharge. This investigation focussed on the Aravali quartzite terrain of Delhi, India at the Research and Referral Hospital and Jawaharlal Nehru University areas. Suitable areas are identified for construction of check dams, roof-top rainwater harvesting pits, and drilling sites in the difficult terrain of the Aravali quartzite.

Application of LiDAR technology for rivers analysis

by Paolo Tarolli

In press in Italian Journal of Engineering Geology and Environment. Co-authored with Marco Cavalli

The availability of high resolution topographic data is strategic for quantitative and qualitative analysis of river... more The availability of high resolution topographic data is strategic for quantitative and qualitative analysis of river environment. The topographic data derived by traditional regional cartography are often too coarse for detailed recognition and mapping of surface morphologic features, while the more accurate data derived by GPS or theodolite are expensive and time-consuming. The airborne laser altimetry technology (LiDAR, Light Detection And Ranging) provides high-resolution topographic data over large areas with high vertical and horizontal accuracy, thus can significantly contribute to a better representation of land surface. A valuable characteristic of this technology, which marks advantages over the traditional topographic survey techniques, is the capability to derive a high-resolution (1 m) Digital Terrain Model (DTM) from the bare ground LiDAR data, by filtering vegetation and man-made features points (buildings, bridges) from raw data. The complex morphology, the wide range of land cover categories, and the presence of deep water bodies, make the airborne LiDAR application in river environments more complicated than application in different contexts. The aim of this work is to highlight the capabilities but also the limitations of airborne LiDAR in river studies, presenting some relevant researches and the main methodological aspects of this technology in fluvial environment.

Innesco di frane superficiali durante eventi di precipitazione brevi ed intensi in zone alpine

by Paolo Tarolli

Published in Quaderni di Idronomia Montana (26), 2006. Co-authored with Marco Borga, Bernardo Cesare, Francesco Zanon, Mauro Tollardo, Pierpaolo Maccon

L’analisi empirica degli eventi di frana e colata detritica ha evidenziato l’importanza del deflusso generato in... more L’analisi empirica degli eventi di frana e colata detritica ha evidenziato l’importanza del deflusso generato in corrispondenza di superfici semiimpermeabili, quali possono essere considerati gli affioramenti rocciosi, sull’innesco di fenomeni di instabilità superficiale delle coltri di suolo dei versanti a valle. La memoria descrive un modello inteso a rappresentare i processi idrologici e geomeccanici che controllano la stabilità dei versanti in tali situazioni. Il modello viene combinato con osservazioni radar di pioggia e consente di determinare un indice, denominato ‘Storm shallow landsliding potential index – SSLIP’, che permette di evidenziare il potenziale di innesco di frana per un evento meteorologico assegnato. Il modello e l’indice così definito sono stati applicati per lo studio dei collassi di versante innescati da due eventi di precipitazione intensa verificatisi in Alto Adige (Valle Aurina) durante l’estate 2005. I risultati conseguiti hanno evidenziato la buona capacità predittiva della metodologia proposta.

A New Method for Determination of Most Likely Landslide Initiation Points and the Evaluation of Digital Terrain Model Scale in Terrain Stability Mapping

by Paolo Tarolli

Published in HESS, 2006. Co-authored with D.G. Tarboton

This paper introduces a new approach for determining the most likely initiation points for landslides from potential... more This paper introduces a new approach for determining the most likely initiation points for landslides from potential instability mapped using a terrain stability model. This approach identifies the location with critical stability index from a terrain stability model on each downslope path from ridge to valley. Any measure of terrain stability may be used with this approach, which here is illustrated using results from SINMAP, and from simply taking slope as an index of potential instability. The relative density of most likely landslide initiation points within and outside mapped landslide scars provides a way to evaluate the effectiveness of a terrain stability measure, even when mapped landslide scars include run out zones, rather than just initiation locations. This relative density was used to evaluate the utility of high resolution terrain data derived from airborne laser altimetry (LIDAR) for a small basin located in the Northeastern Region of Italy. Digital Terrain Models were derived from the LIDAR data for a range of grid cell sizes (from 2 to 50 m). We found appreciable differences between the density of most likely landslide initiation points within and outside mapped landslides with ratios as large as three or more with the highest ratios for a digital terrain model grid cell size of 10 m. This leads to two conclusions: (1) The relative density from a most likely landslide initiation point approach is useful for quantifying the effectiveness of a terrain stability map when mapped landslides do not or can not differentiate between initiation, runout, and depositional areas; and (2) in this study area, where landslides occurred in complexes that were sometimes more than 100 m wide, a digital terrain model scale of 10 m is optimal. Digital terrain model scales larger than 10 m result in loss of resolution that degrades the results, while for digital terrain model scales smaller than 10 m the physical processes responsible for triggering landslides are obscured by smaller scale terrain variability

Analyzing the influence of upslope bedrock outcrops on shallow landsliding

by Paolo Tarolli

Published in Geomorphology, 2008. Co-authored with Marco Borga and Giancarlo Dalla Fontana

A model for the prediction of topographic and climatic control on shallow landsliding in mountainous terrain is... more A model for the prediction of topographic and climatic control on shallow landsliding in mountainous terrain is enhanced to analyse the impact of upslope rocky outcrops on downslope shallow landsliding. The model uses a ‘generalised quasi-dynamic wetness index’ to describe runoff propagation on bare rock surfaces connected to downslope soil-mantled topographic elements. This approach yields a simple enhanced model capable of describing the influence of upslope bedrock outcrops on the pattern of downslope soil saturation. The model is applied in both diagnostic and predictive modes to a small catchment in the eastern Italian Alps for which a detailed inventory of shallow landslides in areas dominated by rocky outcrops is available. In the diagnostic mode, the model is used with satisfactory results to reproduce the pattern of instability generated by an intense short-duration storm occurred on 14 September 1994, which triggered a large percentage of the surveyed landslides. In the predictive mode, the model is used for hazard assessment, and the return time of the critical rainfall needed to cause instability for each topographic element is determined. Modelling results obtained in the predictive mode are evaluated against all the surveyed landslides. It is revealed that the generalised quasi-dynamic model offers considerable improvement over the non-generalised quasi-dynamic model and the steady-state model in predicting existing landslides as represented in the considered landslide inventory.

The effectiveness of airborne LiDAR data in the recognition of channel bed morphology

by Paolo Tarolli

Published in Catena, 2008. Co-authored with Marco Cavalli, Lorenzo Marchi and Giancarlo Dalla Fontana

High-resolution topographic data have the potential to differentiate the main morphological features of a landscape.... more High-resolution topographic data have the potential to differentiate the main morphological features of a landscape. This paper analyses the capability of airborne LiDAR-derived data in the recognition of channel-bed morphology. For the purpose of this study, 0.5 m and 1 m resolution Digital Terrain Models (DTMs) were derived from the last pulse LiDAR data obtained by filtering the vegetation points. The analysis was carried out both at 1-D scale, i.e. along the longitudinal channel profile, and at 2-D scale, taking into account the whole extent of the channel bed. The 1-D approach analyzed the residuals of elevations orthogonal to the regression line drawn along the channel profile and the standard deviation of local slope. The 2-D analysis was based on two roughness indexes, consisting on the local variability of the elevation and slope of the channel bed. The study was conducted in a headwater catchment located in the Eastern Italian Alps. The results suggested a good capability of LiDAR data in the recognition of river morphology giving the potential to distinguish the riffle-pool and step-pool reaches.

Analysis of the headwater basins’ morphology by high resolution LiDAR-derived DTM

by Paolo Tarolli

Published in International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, 2008. Co-authored with Giancarlo Dalla Fontana

High resolution topographic data have the potential to differentiate the main morphological features of a landscape.... more High resolution topographic data have the potential to differentiate the main morphological features of a landscape. For the purpose of this study the Digital Terrain Models (DTMs) ranging between 1m and 20m (cell size) were derived from the last pulse LiDAR data by filtering the vegetation points. We tested the effects of different resolutions in the analysis of river morphology, and potential slope stability. The study was conducted in two headwater catchments located in the eastern Italian Alps where a high-quality set of LiDAR data was available. The results indicated for higher DTM resolutions an improved effectiveness in the recognition of river morphology. Otherwise the progressive finer DTM resolution does not necessarily improve the interpretation of slope stability processes especially if landslides occur at a spatial scale significantly greater than cell size.

LiDAR-derived slopes for headwater channel network analysis

by Paolo Tarolli

Published in Catena, 2009. Co-authored with Alessandro Vianello and Marco Cavalli

Slope is one of the most important distinguishing features for channel morphology. Variations in the computation of... more Slope is one of the most important distinguishing features for channel morphology. Variations in the computation of slope from a digital elevation model can affect a wide range of hydrogeomorphically derived applications. We compare different methods for computing channel slope using LiDAR-derived digital terrain models (DTMs) with varying resolutions. We chose a headwater basin of the Eastern Italian Alps, characterized by a dense ephemeral colluvial network and a main alluvial channel as our study area. The identified alluvial morphologies are characteristic of steep mountain streams, namely, cascades and step pools. Field surveys were carried out along the main channel and in some small tributaries. Results indicate that a single method for slope calculation cannot estimate channel slope at the hydrographic network scale. The differential geometry approach for slope calculation tends to overestimate field-surveyed channel slope values for all the DTM resolutions (1, 2, 5 m). When a trigonometric approach for slope calculation is applied, 2 and 5 m DTM resolutions give more consistent results. Nevertheless, a reliable channel slope can be derived from a DTM with an appropriate resolution by choosing a suitable method only after considering the channel width.

Hillslope-to-valley transition morphology: new opportunities from high resolution DTMs

by Paolo Tarolli

Published in Geomorphology, 2009. Co-authored with Giancarlo Dalla Fontana

The search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental... more The search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental issue in geomorphology. Topographic attributes derived from Digital Terrain Models (DTMs) such as slope, curvature and drainage area provide a basis for topographic analyses. The slope–area relationship has been used to distinguish diffusive (hillslope) from linear (valley) processes, and to infer dominant sediment transport processes. In addition, curvature is also useful in distinguishing the dominant landform process. Recent topographic survey techniques such as LiDAR have permitted detailed topographic analysis by providing high-quality DTMs. This study uses LiDAR-derived DTMs with a spatial scale between 1 and 30 m in order to find the optimal scale for observation of dominant landform processes in a headwater basin in the eastern Italian Alps where shallow landsliding and debris flows are dominant. The analysis considered the scaling regimes of local slope versus drainage area, the spatial distribution of curvature, and field observations of channel head locations. The results indicate that: i) hillslope-to-valley transitions in slope–area diagrams become clearer as the DTM grid size decreases due to the better representation of hillslope morphology, and the topographic signature of valley incision by debris flows and landslides is also best displayed with finer DTMs; ii) regarding the channel head distribution in the slope–area diagrams, the scaling regimes of local slope versus drainage area obtained with grid sizes of 1, 3, and 5 m are more consistent with field data; and iii) the use of thresholds of standard deviation of curvature, particularly at the finest grid size, were proven as a useful and objective methodology for recognizing hollows and related channel heads.

Understanding earth surface processes from remotely sensed digital terrain models

by Paolo Tarolli

Published in Geomorphology, 2009. Co-authored with J Ramon Arrowsmith and Enrique Vivoni

This special issue brings together studies on the innovative use of remotely sensed DTMs for Earth science... more This special issue brings together studies on the innovative use of remotely sensed DTMs for Earth science applications for obtaining new understanding of earth surface processes. The idea for this issue arose from a session on “Remotely sensed DTM for Hydrogeomorphic Applications” convened the proponents as well as William E. Dietrich and Salvatore Grimaldi, during the 2007 Annual Fall Meeting of the American Geophysical Union, held in San Francisco, California. The three oral and one poster sessions attracted 41 abstracts from North America, Europe and Asia, providing an opportunity to review methods, discuss challenges, and evaluate recent technological advances in the use of remotely sensed topographic data for Earth surface processes. Some of the posters and presentations discussed during the meeting sessions were developed into the papers appearing in this special issue. Our goal is to share advances in landscape analysis that are significantly improved by the use of different remotely sensed data sets.We decided to consider a range of remotely sensed technologies in order to offer the scientific community different options and perspectives from recent work. The sequence of contributions is arranged according to the spatial characteristics of the techniques and methods concerned: from very high resolution data collected by TLS, to a progressively coarser resolution data from LiDAR, STRM, and ASTER remotely sensed technology

Suitability of LiDAR point density and derived landform curvature maps for channel network extraction

by Paolo Tarolli

Published in Hydrological Processes, 2010. Co-authored with Francesco Pirotti

This study uses landform curvature as an approach for channel network extraction. We considered a study area located... more This study uses landform curvature as an approach for channel network extraction. We considered a study area located in the eastern Italian Alps where a high-quality set of LiDAR data was available and where channel heads and related channel network were mapped in the field. In the analysis, we derived 1-m DTMs from different ground LiDAR point densities, and we used different smoothing factors for the landscape curvature calculation in order to test the suitability of the LiDAR point density and the derived curvature maps for the recognition of channel network. This methodology is based on threshold values of the curvature calculated as multiples (1–3 times) of the standard deviation of the curvature. Our analyses suggested that (i) the window size for curvature calculations has to be a function of the size of the features to be detected, (ii) a coarse ground LiDAR point density could be as useful as a finer one for the recognition of main channel network features and (iii) rougher curvature maps are not optimal as they do not explore a sufficient range at which features occur, while smoother curvature maps overcome this problem and are more appropriate for the extraction of surveyed channels.

Testing space-scale methodologies for automatic geomorphic feature extraction from LiDAR in a complex mountainous landscape

by Paolo Tarolli

Published in Water Resources Research, 2010. Co-authored with Paola Passalacqua, Efi Foufoula-Georgiou

The next generation of digital elevation data (≤ 3m resolution)
calls for the development of new algorithms for... more The next generation of digital elevation data (≤ 3m resolution)
calls for the development of new algorithms for the objective extraction of geomorphic features, such as channel networks, channel heads, bank geometry, landslide scars, service roads, etc. In this work, we test the performance of two newly developed algorithms for the extraction of geomorphic
features: the wavelet-based extraction methodology developed by Lashermes et al. [2007] and the GeoNet-nonlinear diffusion and geodesic pathsmethodology proposed by Passalacqua et al. [2010]. The study area is part of the Rio Cordon basin, a headwater alpine catchment located in the Dolomites, a mountainous region in the Eastern Italian Alps. The aim of this work is to compare the capability of the two new algorithms in extracting the channel network, capturing channel heads, relevant channel disruptions corresponding to landslides, and representative channel cross-sections. The extracted
channel networks are also compared to the ones obtained using classical methodologies based on an area threshold and an area-slope threshold. A high resolution Digital Terrain Model (DTM) of 1 m served as the basis for such analysis. The results suggest that, although the wavelet-based methodology performs well in the channel network extraction and is able to detect channel heads and channel disruptions, the local nonlinear filter together with the global geodesic optimization used in GeoNet is more robust and computationally efficient, while achieving better localization and extraction of features,
especially in areas where gentle slopes prevail. We conclude that these new methodologies should be considered as valid alternatives to classical methodologies for channel network extraction from lidar, in addition to offering the potential for calibration-free channel source identification and also extraction of additional features of interest.

On the prediction of channel heads in a complex alpine terrain using gridded elevation data

by Paolo Tarolli

Published in Water Resources Research, 2011. Co-authored with Stefano Orlandini, Giancarlo Dalla Fontana, Giovanni Moretti

Threshold conditions for channel initiation are evaluated by using gridded elevation data derived from a lidar survey,... more Threshold conditions for channel initiation are evaluated by using gridded elevation data derived from a lidar survey, a reliable algorithm for the determination of surface flow paths, and field observations of channel heads for a study area located in the eastern Italian Alps. These threshold conditions are determined by considering the channel heads observed across a portion of the study area and computing the related values of (1) drainage area A, (2) area-slope function AS2, S being the local slope, and (3) Strahler order ω∗ 8 of surface flow paths extracted from gridded elevation data. Attention is focused on the dependence of the obtained threshold values on the size of grid cells involved, and on the ability of the identified threshold conditions to provide reliable predictions of channel heads across the entire study area. The results indicate that the threshold values of A, AS2, and ω∗ are all significantly dependent on grid cell size, and the uncertainty in the determination of threshold values of ω∗ is significantly smaller than that affecting the determination of threshold values of A and AS2. The comparison between predicted and observed channel heads indicates that the considered methods display variable reliability and sensitivity over different drainage basins and grid cell sizes, with a general tendency to predict more channel heads than can be observed in the field. Acceptable predictions are normally obtained where channel heads are formed essentially by surface erosion. More comprehensive methods seem, however, to be needed to predict channel heads affected by groundwater seeping upwards.

An objective approach for feature extraction: distribution analysis and statistical descriptors for scale choice and channel network identification

by Paolo Tarolli

Published in HESS, 2011. Co-authored with Giulia Sofia, Federico Cazorzi, Giancarlo Dalla Fontana

A statistical approach to LiDAR derived topographic attributes for the automatic extraction of channel network and for... more A statistical approach to LiDAR derived topographic attributes for the automatic extraction of channel network and for the choice of the scale to apply for parameter evaluation is presented in this paper. The basis of this approach is to use distribution analysis and statistical descriptors to identify channels where terrain geometry denotes significant convergences. Two case study areas with different morphology and degree of organization are used with their 1 m LiDAR Digital Terrain Models (DTMs). Topographic attribute maps (curvature and openness) for various window sizes are derived from the DTMs in order to detect surface convergences. A statistical analysis on value distributions considering each window size is carried out for the choice of the optimum kernel. We propose a three-step method to extract the network based (a) on the normalization and overlapping of openness and minimum curvature to highlight the more likely surface convergences, (b) a weighting of the upslope area according to these normalized maps to identify drainage flow paths and flow accumulation consistent with terrain geometry, (c) the standard score normalization of the weighted upslope area and the use of standard score values as non subjective threshold for channel network identification. As a final step for optimal definition and representation of the whole network, a noise-filtering and connection procedure is applied. The advantage of the proposed methodology, and the efficiency and accurate localization of extracted features are demonstrated using LiDAR data of two different areas and comparing both extractions with field surveyed networks.

Application of LiDAR technology for rivers analysis

by Paolo Tarolli

In press in Italian Journal of Engineering Geology and Environment. Co-authored with Marco Cavalli

The availability of high resolution topographic data is strategic for quantitative and qualitative analysis of river... more The availability of high resolution topographic data is strategic for quantitative and qualitative analysis of river environment. The topographic data derived by traditional regional cartography are often too coarse for detailed recognition and mapping of surface morphologic features, while the more accurate data derived by GPS or theodolite are expensive and time-consuming. The airborne laser altimetry technology (LiDAR, Light Detection And Ranging) provides high-resolution topographic data over large areas with high vertical and horizontal accuracy, thus can significantly contribute to a better representation of land surface. A valuable characteristic of this technology, which marks advantages over the traditional topographic survey techniques, is the capability to derive a high-resolution (1 m) Digital Terrain Model (DTM) from the bare ground LiDAR data, by filtering vegetation and man-made features points (buildings, bridges) from raw data. The complex morphology, the wide range of land cover categories, and the presence of deep water bodies, make the airborne LiDAR application in river environments more complicated than application in different contexts. The aim of this work is to highlight the capabilities but also the limitations of airborne LiDAR in river studies, presenting some relevant researches and the main methodological aspects of this technology in fluvial environment.

الموارد المائية والتنمية المستدامة في السهل الساحلي الجنوبي الغربي لليمن

by Dr.Kadri Abdulbaki

للمزيد عن مؤشرات التنمية المستدامة http://www.un.org/esa/sustdev/natlinfo/indicators/methodology_sheets.pdf

ملخص بحث :
الموارد المائية والتنمية المستدامة في السهل الساحلي الجنوبي الغربي لليمن
مقدم إلى الملتقى... more ملخص بحث :
الموارد المائية والتنمية المستدامة في السهل الساحلي الجنوبي الغربي لليمن
مقدم إلى الملتقى الخامس للجغرافيين العرب الذي انعقد في دولة الكويت في ابريل 2009 م
أ.د.قادري عبد الباقي أحمد
نائب رئيس المجلس التنفيذي للجمعية الجغرافية اليمنية
قسم الجغرافيا – كلية الآداب – جامعة عدن – اليمن
الكلمات المفتاحية : موارد المياه , التنمية المستدامة , التنمية الحضرية , التنمية الزراعية .

تقع منطقة الدراسة : مدينة عدن , دلتا أبين ودلتا تبن , في السهل الساحلي الجنوبي الغربي لليمن بين خطي عرض44.49 - 45.29 شرقا , وهي تمتد من خط الساحل جنوبا وحتى أقدام الجبال الساحلية على بعد 35 كلم في المتوسط . هنا تتفاعل كل من التنمية الحضرية والتنمية الزراعية وتتنافس على الموارد المائية الشحيحة المتاحة فيها وخاصة موارد المياه الجوفية , الأمر الذي أثر بهذا القدر أو ذاك على منظومة التنمية المستدامة : المجتمع – الاقتصاد – البيئة .
وتعتبر مدينة عدن أكبر مركز حضري في منطقة الدراسة فضلا عن عدة مراكز حضرية ثانوية تقع في دلتا أبين ودلتا تبن المجاورتين لمدينة عدن . ووفقا لتعداد عام 2004 م بلغ عدد السكان في منطقة الدراسة 833312 نسمة استأثرت مدينة عدن وحدها بنحو 70.73 % من إجمالي عدد السكان في حين توزعت النسبة الباقية على دلتا أبين 16.15 % ودلتا تبن 13.12 % .
وبالنظر إلى تعدد الوظائف الحضرية لمدينة عدن والمتمثلة بالوظيفة التجارية والسياحية , ولموقعها المتميز على خط الملاحة الدولية وموقع نشاط ميناء عدن في الحياة الاقتصادية للمدينة , كل ذلك التطور والتنمية الاقتصادية أسهم منذ منتصف القرن العشرين في تنمية حضرية كان أبرز معالمها وخصائصها اتجاهات النمو الحضري للمدينة وتوسع التركيب الداخلي لها وزيادة الطلب على الموارد المائية لتلبية الاحتياجات الحضرية وللأنشطة الاقتصادية المختلفة , وذلك بالاعتماد على خزانات المياه الجوفية في كل من دلتا تبن ودلتا أبين .
وبالمقابل تعد كل من دلتا تبن ودلتا أبين الممتدتان شمال وشمال شرق مدينة عدن على التوالي أهم المناطق الزراعية في السهل الساحلي الجنوبي الغربي لليمن. حاليا تقدر الأراضي الخصبة القابلة للزراعة بحوالي 90 ألف هكتار ؛ 67.5 % منها توجد في دلتا أبين والباقي في دلتا تبن , مع نسبة محدودة تقدر بنحو 3 % تقع في ضواحي مدينة عدن .
ويقدر متوسط حجم المياه السطحية المتدفقة سنويا إلى دلتا أبين وإلى دلتا تبن حوالي 194 - 127 مليون متر مكعب على التوالي في حين قدر حجم التغذية السنوية للمياه الجوفية في دلتا أبين ودلتا تبن حوالي 94 - 112 مليون متر مكعب على التوالي . وعلى قلتها كانت هذه الموارد المائية ولا تزال مفتاح التنمية وتأتي في طليعة متطلبات التنمية الزراعة. وقد تمكن الإنسان هنا منذ ستينات القرن الماضي من الاستفادة القصوى من مياه السيول في مواسم تدفقها وتحويلها عبر منظومة متكاملة من شبكة الري السطحي إلى الأراضي الزراعية وتأمين احتياجات السكان من الخضروات والفواكه فضلا عن زراع القطن والأعلاف والحبوب. ومع ذلك فأن الكفاءة ة المنخفضة للري السطحي وضعف السيطرة على السيول الكبرى التي تسببت في عدة كوارث طبيعية وانصرفت هدرا إلى البحر فضلا عن تدهور الأراضي , كل ذلك يؤشر إلى تنمية زراعية غير مستدامة . من جانب آخر ونظرا لسيادة الظروف المناخية الجافة القاحلة وتذبذب الحجم السنوي لتصريف السيول اتجهت الزراعة إلى موارد المياه الجوفية وخاصة في الأجزاء الجنوبية القريبة من البحر منافسة بذلك قطاع تموينات المياه لأغراض التنمية الحضرية الأمر الذي نتج عنه هبوطا سريعا لمناسيب المياه الجوفية وتدهور نوعي وكمي لمواصفات المياه الصالحة للاستخدام البشري .
ولتأمين متطلبات التنمية الحضرية والتنمية الزراعية من المياه الآمنة صحيا والصالحة للري تم تنفيذ عدد من الإجراءات في ثمانينات القرن الماضي للحد من تدهور الموارد المائية الجوفية , وذلك من خلال تشريعات تمنع الحفر العشوائي للآبار وتحرمه في مناطق حقول مصادر تموينات المياه للأغراض الحضرية فضلا عن تأمين مصادر بديلة لتموينات المياه . غير أن الطفرة الديموغرافية والتنموية التي أعقبت توحد اليمن عام 1990 م أفرزت عدة إشكاليات بحثية وتطبيقية لمسألة الموارد المائية والتنمية المستدامة في منطقة الدراسة تتمثل في اختلالات التوازن بين متطلبات التنمية الحضرية والتنمية الزراعية من الموارد المائية من جهة وبين هذه الأخيرة و الاحتياجات البيئية للحفاظ على التنوع الحيوي في إطار الحفاظ على التنوع الحيوي من جهة أخرى , فضلا عن اختلالات التنمية المستدامة بين واقع الاحتياجات القائمة والاحتياجات المستقبلية من هذه الموارد ؛ تعكسها مجموعة من مؤشرات التنمية المستدامة .
ولتحليل تلك الاختلالات في القطاعين الحضري والزراعي في مدينة عدن ودلتا أبين ودلتا تبن في ارتباطهما بالموارد المائية المتاحة التي تشكل منظومة هيدرولوجية واحدة في التقسيم الإداري اليمني لموارد المياه , اعتمد على مؤشرات التنمية المستدامة التالية : مؤشر مواصفات المياه ودرجة تلوثها وطرق معالجتها وتحديد نسبة السكان الحاصلين على مياه آمنة صحيا والأساليب المتبعة في إدارة التنافس بين المستفيدين من الموارد المائية . وكذا مؤشر الإدارة البيئية للمياه ومؤشر العلاقة بين موارد المياه والسكان وتحديد معدلات نصيب الفرد من المياه يوميا فضلا عن المؤشرات المرتبطة بالتنمية الزراعية مثل مؤشر تدهور التربة والإنتاجية الزراعية واتجاهات التغير في الهيكل المحصولي الزراعي . وعلى سبيل المثال انخفض معدل نصيب الفرد من المياه في مدينة عدن من 182 لتر / اليوم عام 1990م إلى 83 لتر / اليوم عام 2006 م . من جهة أخرى تقلصت مساحات الرقعة الزراعية بسبب النمو العمراني وانخفضت مناسيب المياه الجوفية بسبب الحفر العشوائي للآبار وزيادة حجم المياه المسحوبة لأغراض الري رغم تدهور مواصفاتها ما أثر في الإنتاجية الزراعية للمحاصيل وبالتالي واقع ومستقبل التنمية الزراعية في منطقة الدراسة .
كما ساعد استخدام عدة طرق وأدوات بحثية : مثل أدوات نمذجة التوازن المائي بين العرض والطلب والتحليل المتعدد الجوانب لتحديد وتفسير أنماط العلاقات بين مختلف جوانب منظومة التنمية في منطقة الدراسة المستفيدة من الموارد المائية فضلا عن الأساليب الإحصائية للتنبؤ بالأوضاع المستقبلية حتى عام2025 م , على اقتراح التصورات الممكنة لمواجهة تحديات الألفية في مجال المياه وآفاق التنمية الحضرية والتنمية الزراعية في منطقة الدراسة .

عدن مارس 2008 م

Combining a fuzzy optimal model with a genetic algorithm to solve multi-objective rainfall-runoff model calibration

by K.W. Chau

Cheng, C.T., Ou, C.P., Chau, K.W. Journal of Hydrology 268 (1-4), pp. 72-86, 2002

An automatic calibration methodology for the Xinanjiang model that has been successfully and widely applied in China... more An automatic calibration methodology for the Xinanjiang model that has been successfully and widely applied in China is presented. The automatic calibration of the model consists of two parts: water balance parameter and runoff routing parameter calibration. The former is based on a simple genetic algorithm (GA). The latter is based on a new method which combines a fuzzy optimal model (FOM) with a GA for solving the multiple objective runoff routing parameters calibration problem. Except for the specific fitness where the membership degree of alternative obtained by FOM with limited alternatives and multi-objectives is employed, the GA with multiple objectives in this paper is otherwise the same as the simple GA. The parameter calibration includes optimization of multiple objectives: (1) peak discharge, (2) peak time and (3) total runoff volume. Thirty-four historical floods from 12 years in the Shuangpai Reservoir are applied to calibrate the model parameters whilst 11 floods in recent 2 years are utilized to verify these parameters. Results of this study and application show that the hybrid methodology of GAs and the FOM is not only capable of exploiting more the important characteristics of floods but also efficient and robust.