Groundwater Table Depth Research Articles

Regionalizing ecological moisture levels and groundwater levels in grassland areas using thermal remote sensing

AbstractSite‐specific soil moisture and groundwater levels are key input parameters for ecological modeling. Obtaining such information in a comprehensive manner is difficult for large regions. We studied a floodplain region in the Federal State of Brandenburg, Germany, to examine the degree to which the average depth of groundwater tables can be derived from surface temperatures obtained by the ASTER radiospectrometer (spatial resolution of 90 m per pixel). A floristic ecological indicator representing the site‐specific moisture level was applied to develop a proxy between the thermal satellite data and groundwater table depth. The use of spring scenes (late April to early May) from 2 years proved to be well suited for minimizing the effects of weather and land use. Vegetation surveys along transects that were 2 m wide across the pixel diagonals allowed for the calculation of average ‘ecological moisture values’ of pixel‐sites by applying ‘Ellenberg‐numbers’. These values were used to calibrate the satellite data locally. There was a close relationship between surface temperature and the average ecological moisture value (R2 = 0.73). Average ecological moisture values were highly indicative of the average groundwater levels during a 7‐year measurement series (R2 = 0.93). Satellite‐supported thermal data from spring were suitable for estimating the average groundwater levels of low‐lying grasslands on a larger scale. Ecological moisture values from the transect surveys effectively allowed the incorporation of relief heterogeneity within the thermal grid and the establishment of the correlation between thermal data and average groundwater table depth. Regression functions were used to produce a map of groundwater levels at the study site.

Impact of Environmental Site Location and Groundwater Table Depth on Thickness of Flexible Airfield Pavements

This comprehensive sensitivity study of a newly developed computer code at Arizona State University incorporates the influence of environmental site factors and the groundwater table depth on flexible airfield pavement design and performance. The newly developed code, called ZAPRAM, is a mechanistically based pavement model based on limiting strain criteria. The completed study used the newly revised U.S. Army Corps of Engineers failure criteria for subgrade shear deformation. The experimental factorial conducted comprised three aircraft types, three levels of as-compacted (optimum) subgrade condition, two levels of design aircraft passes, and an environmental combination of six groundwater table depths and five environmentally different city locations. The methodology used in this study applied the same analytical method to achieve real-time environmental effects on unbound layer modulus as the new AASHTO Mechanistic–Empirical Pavement Design Guide. The results of this effort showed for the first time the quantitative impact of the significant effects of climatic conditions at the design site, coupled with the importance of the depth of the groundwater table, on the predicted design thicknesses. Significant cost savings appear to be quite reasonable by using the principles of unsaturated soil mechanics in the new airfield pavement design procedure in ZAPRAM.

哀牢山常绿阔叶林水源涵养功能及其在应对西南干旱中的作用

Southwest China experienced the most severe drought in 100 years in the late 2009 and early 2010.The effects of this severe drought event on forest ecosystems in this region were un-assessed.The aims of this study were(1) to assess if the evergreen broadleaf forest in Ailao Mountain,Southwest China,experienced water deficits in the 2010 rainfall anomaly event;(2) to understand the contribution of forest water storages in mitigating the effects of rainfall anomaly events;and(3) to assess the effects of logging on the water-holding capacity of an ecosystem.Water status of soils and major tree species from a primary evergreen broadleaf forest in Ailao Mountain were monitored in the 2010 dry season.Soil and litter water-holding capacities of a primary forest and a secondary Yushania-Pteridium shrub-land formed after logging and burn were compared.Inter-annual and seasonal variations in soil groundwater table and relative water content of the forest and the Yushania-Pteridium shrub-land were also analyzed.Trees in the evergreen broadleaf forest did not experience water deficits even in the driest month(predawn leaf water potential was higher than-0.5 MPa),and the photosynthetic performance of the trees did not show symptom of long-term depression(predawn maximum quantum efficiency of Photosystem II was higher than 0.80).Soil water content and groundwater table depth of the forest reached an historical minimum during the 2010 Southwest China rainfall anomaly event,however enough soil water was still available for plants during the driest month of 2010(water potential of the soil layer where the roots were growing was still higher than-0.5 MPa).The soil water potential of the evergreen broadleaf forest was higher than the Yushania-Pteridium shrub-land,suggesting better water availability for plants in the primary forest compared to the secondary Yushania-Pteridium shrub-land.The relatively high soil water availability of the primary evergreen broadleaf forest during the rainfall anomaly event is because of its good water-holding capacity,which allows sufficient rainfall in the wet season to be stored in the soil,and to be available to plants in the dry season.The soil water-holding capacity,especially noncapillary water-holding capacity of the evergreen broadleaf forest soils in Ailao Mountain was higher than that of the Yushania-Pteridium shrub-land soils,and higher than those of some other secondary forests in this region.In addition,the abundant litters in the forest floor also contribute to the water storage function of the forest through holding water,preventing evaporation,and decreasing surface runoff.The seasonal dynamics in ground water table and soil relative water content also suggest a larger soil water-storage-pool size of the forest than that of the Yushania-Pteridium shrub-land.In conclusion,the evergreen broadleaf forests in Ailao Mountain possess a strong water storage function,and the sufficient ground water and soil water storages mitigated the shortage of rainfall in dry seasons and in severe rainfall anomaly events.Therefore,our study suggests the irreplaceable role of primary forests in mitigating the effects of rainfall anomaly events,and the importance of protecting primary forests in enhancing the capacity of this region in coping with rainfall anomaly events.

EFFECT OF GROUNDWATER LEVEL DEPTH AND IRRIGATION AMOUNT ON WATER FLUXES AT THE GROUNDWATER TABLE AND WATER USE OF WHEAT

ABSTRACTThree irrigation water regimes (90.0, 67.5, and 45.0 mm) and five groundwater table depths (1.5, 2.0, 2.5, 3.0, and 3.5 m) were considered in a lysimeter experiment to investigate the effect of groundwater level and irrigation amount on water fluxes at the groundwater table and water use of wheat. Results show that deep percolation (irrigation of 16–23%) occurred to a considerable extent in the present irrigation level at a shallow groundwater table of 1.5–2.0 m. Capillary rise comprised 29% of the water use of wheat, within the period from regreening to harvest, at 1.5 m groundwater table depth, and was reduced with an increase in table depth. A relationship between groundwater contribution and groundwater table depth was also found. In the present irrigation conditions, the water productivity (WPb) of wheat was enhanced from 3.59 kg m‐3 at a shallower groundwater level depth of 1.5 m, to 4.58 kg m‐3 at a deeper groundwater level depth of 3.5 m. WPb can be higher if deficit irrigation is enforced and can reach 3.93–6.03 kg m‐3. Similarly, a relationship between WPb and groundwater table depth was found. Hence, the irrigation amount per time for local wheat can be reduced to 45.0–67.5 mm, depending on the groundwater level depth, in order to use water resources effectively. Copyright © 2011 John Wiley & Sons, Ltd.

Field-evaluation of DRAINMOD-S for predicting soil and drainage water salinity under semi-arid conditions in Turkey

The aim of this study was to determine the reliability of DRAINMOD-S for simulating water management in irrigated land and to simulate drainage system design criteria to ensure high crop yields for the western part of the Central Kızılırmak Basin in Turkey. The model was tested under arid conditions using field data for winter wheat and corn. Daily water-table depth, drain outflows and drainage water salinity were monitored throughout the growing season. Soil salinities were measured to a depth of 1.00 m from the soil surface. The reliability of the model was evaluated by comparing measured and predicted values of the daily ground water table depth, drain outflows, drainage water and soil salinity during each season, and relative crop yield. Good agreement was found between the measured and predicted values. Absolute deviation was 5.68 cm for water table depth, 10.13 mm for drain outflows, 0.66 dS m–1 for drainage water salinity, and ranged from 0.51 to 0.96 dS m–1 for soil salinity. The corresponding coefficients of efficiency (E) were between 0.48 and 0.95. The results also showed that Drainmod -S can be recommended as a useful tool for design and evaluation of irrigation and drainage systems in salt-affected soils under arid and semi-arid climates.

Groundwater Hydrograph Patterns in North China Plain during 1982-1986 Interpreted Using Principal Component Analysis

The groundwater table depths from 1982 to 1986 of 58 unconfined wells in North China Plain(NCP) were analyzed using principal component analysis method. Results showed there were mainly three hydrograph patterns over the area: increasing trend with steady moderate seasonal fluctuations in Taihang Mountain piedmont area; decreasing trend with large seasonal fluctuation magnitudes in central plain of NCP; increasing-decreasing trend with large variance of fluctuation magnitude in piedmont of Yan Mountain piedmont.The distribution of precipitation, irrigating abstraction, and water table depths were the main factors determining the hydrograph patterns and their distribution.

Numerical modeling groundwater recharge and its implication in water cycles of two interdunal valleys in the Sand Hills of Nebraska

The topography and geomorphology of the sand dunes and interdunal valleys in the Nebraska Sand Hills play important roles in regional water cycle by influencing groundwater recharge and evapotranspiration (ET). In this study, groundwater recharge, associated with precipitation and ET as well as soil hydraulics, and its spatial variations owing to the topography of dunes and valleys are examined. A method is developed to describe the recharge as a function of the storage capacity of dunes of various heights. After the method is tested using observations from a network of wells in the Sand Hills, it is used in the MODFLOW model to simulate and describe recharge effects on groundwater table depth at two different dune-valley sites. Analysis of modeled groundwater budget shows that the groundwater table depth in the interdunal valleys is critically influenced by vertical groundwater flows from surrounding dunes. At the site of higher dunes there are steadier and larger vertical groundwater flows in the dunes from their previous storage of precipitation. These vertical flows change to be horizontal converging groundwater flows and create upwelling in the interdunal valleys, where larger ET loss at the surface further enhances groundwater upwelling. Such interdunal valley is the major concentration area of the surface water and groundwater flow in the Sand Hills. At the site of shallow dunes and a broad interdunal valley the supply of groundwater from the dunes is trivial and inadequate to support upwelling of groundwater in the valley. The groundwater flows downward in the valley, and the valley surface is dry. Weak ET loss at the surface has a smaller effect on the groundwater storage than the precipitation recharge, making such area a source for groundwater.

Study on capillary rise from shallow groundwater and critical water table depth of a saline-sodic soil in western Songnen plain of China

The objective of this study was to develop an empirical equation for estimating the capillary rise in the saline-sodic soil area of Songnen Plain in China based on the Averianov formula. The capillary rise was observed under five controlled groundwater levels by lysimeters. Field experiment results indicated that capillary rise had close relationship with the groundwater table depth, soil moisture of 10–40 cm soil layer and leaf area index. These factors have been taken into account to develop the empirical equation for capillary rise simulation. The model parameters for Songnen Plain were derived by Levenberg–Marquardt and global optimization calculating method. The modeled capillary rise has a good agreement with the observed data (r 2 = 0.875). With the simulation model, the critical water table depth was identified as 2.5 m, indicating that soil secondary salinization will not occur when the water table depth is deeper than 2.5 m. Therefore, in the irrigation areas, groundwater table depth should be controlled to be higher than 2.5 m to prevent the occurrence of soil secondary salinization. The results from this research will provide useful information for the water sources management and soil secondary salinization control in Songnen Plain of China, one of the most serious saline-affected areas in the world.

Determining optimal groundwater table depth for maximizing cotton production in the Sardarya province of Uzbekistan

AbstractPoor on‐farm irrigation practices and rising groundwater table depths are the major reasons for low cotton yields in the Sardarya province of Uzbekistan. To ensure sustainability of cotton production in the area, precise calculations of irrigation requirements are needed to optimize crop yields and to keep groundwater table depth below the root zone to avoid soil salinization. To determine optimal groundwater table depth and irrigation amounts for the Sardarya province of Uzbekistan, the Soil–Water–Atmosphere–Plant (SWAP) model was used. SWAP was calibrated and validated using measured data from an experimental cotton field during the agricultural year of 2006 and 2007. The calibrated SWAP model was then used to simulate optimal groundwater table depth and irrigation amounts. The simulation results show that for the existing conditions in the study area, a groundwater table depth of approximately 200 cm together with an irrigation application of 2500 m3 ha−1 will be the most appropriate combination for optimal cotton yields (≈ 3.0 t ha−1). However, to achieve maximum potential yields of cotton (5–6 t ha−1), leaching of excessive salts from the root zone through freshwater application would be imperative. This would require rehabilitation of the existing drainage network in the area. Copyright © 2010 John Wiley & Sons, Ltd.

Vegetation dynamics induced by groundwater fluctuations in the lower Heihe River Basin, northwestern China

Aims Since 2000, the environmental flow controls project has been implemented in the lower Heihe River Basin, a typical arid inland river basin in northwest China, to restore the deteriorated ecological environment in this region. The aim of this study was to explore the impacts of groundwater fluctuations on vegetation dynamics. Our results can be used as a reference for water resources planning and management to maintain proper environmental flows in arid areas. Methods The location (by Global Positioning System) and depth of the monitoring wells, as well as groundwater table depth and salinity were measured in situ at each site from July to August 2009. Based on the measurements of the groundwater table depth and salinity following the implementation of environmental flow controls project (EFCP) in the lower Heihe River Basin, the groundwater fluctuations during the period from 2001 to 2009 were analyzed. Descriptive statistics and Pearson’s correlation were used to analyze the relationship between vegetation changes and groundwater table fluctuations. Additionally, the spatial distributions of the groundwater table depth and salinity were interpolated using the simple kriging method. Trend analysis was applied to the time series of integrated Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index data to identify interannual vegetation dynamics. The relationship between vegetation status and groundwater environment was investigated at different spatial scales by analyzing and comparing the time series and trends. Important Findings (i) The groundwater table and salinity increased significantly in most of the study area with spatial heterogeneity. On average, the groundwater table rose ;0.5 and 1.5 m in the upper and lower Ejina Basin, respectively, and the groundwater salinity increased across the study area by 0–4%. (ii) A notable correlation between the vegetation status and the groundwater table was revealed when the groundwater table depth fluctuated between 1.8 and 3.5 m, whereas the vegetation did not show an obvious response to groundwater table changes when the groundwater table depth was more than 5–6 m. (iii) Vegetation restoration mainly occurred in riparian areas within 500–1 000 m of from natural rivers, where the groundwater table depth varied from 2 to 4 m, and salinity was <5%, whereas vegetation degradation appeared at some locations where groundwater environment had deteriorated.

Evaluation of modified DRAINMOD in predicting groundwater table fluctuations and yield of canola in paddy fields under snowy conditions (case study: Rasht Iran)

AbstractThe computer simulation hydrologic model DRAINMOD and modified DRAINMOD (Luo et al. 2000) for cold condition was used to predict the performance of surface drainage and yield of canola as post‐rice cultivation during the wet growing season of 2004–2005 in Rasht Iran.Performance of surface drainage system treatments with 2 m spacing and 15 cm drain depth as compared with plots having no drainage (4 × 10 m2) were used to evaluate the models. Evaluation of predicted daily groundwater table depths as compared with measured values shows that the root mean square error (RMSE) was about 10.2 and 9.9 cm for DRAINMOD versus 11.0 and 11.5 for modified DRAINMOD in 2 m drain spacing and no drainage treatment respectively. Original DRAINMOD and modified DRAINMOD predictions for groundwater table depth was on average about 4 and 7% less than measured values for the surface drainage treatment and 22 and 14% greater for the no drainage treatment whereas the standard error of original DRAINMOD was 1.4 and 1.51 (cm) respectively. The average absolute deviations were 8.67 and 9.22 (cm). However by using the modified DRAINMOD these values were decreased to 1.34 1.3 8.05 and 8.19 cm respectively.Comparisons show that modifications introduced in DRAINMOD for snowy conditions improved the capability of the model to predict groundwater table fluctuations. Copyright © 2011 John Wiley &amp; Sons Ltd.

The variation in soil moisture and the appropriate groundwater table for desert riparian forest along the Lower Tarim River

Based on data collected over five years of monitoring the Lower Tarim River, we analyzed the variability of soil moisture content (SMC) and the relationship between SMC, groundwater table depth (GWD) and vegetation by using the methods of coefficient of variation (Cv), Pearson correlation and regression. The results of the variability of SMC indicate that it rose with increase in depth of soil layer — SMC in the soil layer of 0–60 cm was relatively small compared to SMC in the soil layer of 100–260 cm which showed a significant increase in variability. SMC and GWD before and after ecological water diversions exhibited significant differences at the site of the Yingsu transect and its vicinity of the watercourse, especially SMC in the soil layer of 100–260 cm increased significantly with a significant rise of GWD and reached maximum values at a GWD of about 4 m. Plant coverage and species diversity significantly improved with increases in SMC in the soil layer of 100–260 cm, both of them approached the maximum values and 92.3% of major plant species were able to grow when SMC was > 10%. To restore the ecosystem of desert riparian forest along the Lower Tarim River, the GWD must be maintained at < 4 m in the vicinity of the watercourse and at about 4 m for the rest of this arid region.

The role of grasslands in the formation of structural and spatial order of rural areas

The paper presents results of a two-year study on methane emission carried out in lysimetric station situated on Kuwasy peatland in the Biebrza River valley. The aim of this study was to estimate the amount of methane emission from peat-muck soil in relation to ground water level and fertilisation. Methane emission was determined with the chamber method using photo-acoustic probe. Methane emission significantly depended on the ground water level. The largest CH4 emission was found at full saturation of soil with water. With the decrease of ground water table the emission of methane decreased. Mineral fertilisation increased CH4 emission. At ground water table depth of 50 cm, CH4 emission from fertilised variant was by 42.3% bigger than from non-fertilised variant. Peat-muck soils overgrown by meadows in the Biebrza River valley were found to be an important source of methane emission. In the vegetation period at ground water table depths of 0, 25, 50 and 75 cm methane emission was 502, 361, 198, 141 kg·ha –1 ·(210 d) –1 , respectively.

Comparison of the monitored and modeled soil water storage of the upper soil layer: the influence of soil properties and groundwater table level

Comparison of the monitored and modeled soil water storage of the upper soil layer: the influence of soil properties and groundwater table levelIn the study ofTomlain(1997) a soil water balance model was applied to evaluate the climate change impacts on the soil water storage in the Hurbanovo locality (Southwestern Slovakia), using the climate change scenarios of Slovakia for the years 2010, 2030, and 2075 by the global circulation models CCCM, GISS and GFD3. These calculations did not take into consideration neither the various soil properties, nor the groundwater table influence on soil water content. In this study, their calculated data were compared with those monitored at the same sites. There were found significant differences between resulting soil water storage of the upper 100 cm soil layer, most probably due to cappilary rise from groundwater at sites 2 and 3. It was shown, that the soil properties and groundwater table depth are importat features strongly influencing soil water content of the upper soil layer; thus the application of the soil water balance equation (Eq. (1)), neglecting the above mentioned factors, could lead to the results far from reality.

Within‐Field Variability of Bare Soil Evaporation Derived from Eddy Covariance Measurements

Bare soil evaporation was measured with the eddy‐covariance method at the Selhausen field site. The site has a distinct gradient in soil texture, with a considerably higher stone content at the upper part of the field. We investigated the effect of different soil properties in the upper and lower parts of the field on evaporation using eddy covariance (EC) measurements that were combined with a footprint model. Because only one EC station was available, simultaneous evaporation measurements from the two field parts were not available. Therefore, measurements were put into the context of meteorologic and soil hydrologic conditions. Meteorologic conditions were represented by the potential evaporation, i.e., the maximum evaporation that is determined by the energy available for evaporation. The influence of precipitation and soil hydrologic conditions on the actual evaporation rate was represented by a simple soil evaporation model. The amount of water that could be evaporated at the potential rate from the lower part of the field was found to be large and considerably larger than from the upper part of the field. The difference in evaporation led to threefold larger predicted percolation or runoff in the upper than the lower part of the field. Simulations using the Richards equation were able to reproduce the differences in evaporation between the lower and upper parts of the field and relate them to the different groundwater table depths in the two parts of the field.

A multivariate analysis of covariance to determine the effects of near-stream best management practices on nitrogen and phosphorus concentrations on a dairy farm in the New York Conservation Effects Assessment Project watershed

Near-stream best management practices (BMPs), such as exclusionary fencing or cattle crossings, are often recommended to improve water quality, but quantification of their impacts is limited. Surface and subsurface processes in these near-stream areas impact the contribution of nitrogen and phosphorus to watercourses and the effectiveness of near-stream BMPs. To test the impact of the near-stream BMPs, groundwater samples from 30 piezometers and streamwater samples along two adjacent creeks (one control and one with BMP treatment) were collected over a three-year period before and after installation of exclusionary fencing with a cattle crossing in the Catskill Mountains of New York State. Samples were analyzed for nitrate nitrogen (NO₃⁻-N), soluble reactive phosphorus (SRP), dissolved oxygen, and dissolved organic carbon. Analysis results and other ancillary variables (rainfall and groundwater table depth) were incorporated into a multivariate statistical model to evaluate the impact of the BMPs on the concentrations of NO₃⁻-N and SRP in the treatment creek. Results of the analysis indicate that the installation of the near-stream BMPs resulted in a 27% yearly (34% during the growing season) reduction in treatment creek SRP concentrations, while there was little impact on NO₃⁻-N concentrations. Incorporating the SRP concentrations measured in a nearby control creek and controlling for the effects of groundwater SRP levels and groundwater hydrology (water table height) had a significant effect on the overall analytical model performance. These results indicate that protecting near-stream areas from potentially pollution-causing practices can be an important means of controlling phosphorus levels in water bodies.

Landscape structure, groundwater dynamics, and soil water content influence soil respiration across riparian–hillslope transitions in the Tenderfoot Creek Experimental Forest, Montana

AbstractVariability in soil respiration at various spatial and temporal scales has been the focus of much research over the last decade aimed to improve our understanding and parameterization of physical and environmental controls on this flux. However, few studies have assessed the control of landscape position and groundwater table dynamics on the spatiotemporal variability of soil respiration. We investigated growing season soil respiration in a ∼393 ha subalpine watershed in Montana across eight riparian–hillslope transitions that differed in slope, upslope accumulated area (UAA), aspect, and groundwater table dynamics. We collected daily‐to‐weekly measurements of soil water content (SWC), soil temperature, soil CO2 concentrations, surface CO2 efflux, and groundwater table depth, as well as soil C and N concentrations at 32 locations from June to August 2005. Instantaneous soil surface CO2 efflux was not significantly different within or among riparian and hillslope zones at monthly timescales. However, cumulative integration of CO2 efflux during the 83‐day growing season showed that efflux in the wetter riparian zones was ∼25% greater than in the adjacent drier hillslopes. Furthermore, greater cumulative growing season efflux occurred in areas with high UAA and gentle slopes, where groundwater tables were higher and more persistent. Our findings reveal the influence of landscape position and groundwater table dynamics on riparian versus hillslope soil CO2 efflux and the importance of time integration for assessment of soil CO2 dynamics, which is critical for landscape‐scale simulation and modelling of soil CO2 efflux in complex landscapes. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Prediction of water table depth in a hard rock basin by using artificial neural network

The objectives of this study were to determine the factors that influence and control the water table fluctuation in a specific geomorphologic situation, to develop a forecasting model and examine its potential in predicting water table depth using limited data. Prediction of region specific water table fluctuation would certainly guide the way towards conceiving, designing and taking scientific measures to ensure sustainable groundwater management. Analysis of change in groundwater table depth, groundwater flow directions within the watershed showed that the influencing factors of rainfall, groundwater draft from near by structures and the resulting fluctuation in groundwater table depth were well correlated in a specific geological situation. Models for prediction of water table depth were developed based on artificial neural networks (ANNs). The study employed multilayer feed forward neural network with backpropagation learning method to develop the model. The neural networks with different numbers of hidden layer neurons were developed using 4 years (2005 - 2008) monthly rainfall, potential evapotranspiration (PET), and water table depth from nearby, influencing wells data as input and one month ahead water table depth as output. The best model was selected based on the root mean square error (RMSE) of prediction using independent test data set. The results of the study clearly showed that ANN can be used to predict water table depth in a hard rock aquifer with reasonably good accuracy even in case of limited data situation. Key words: Water table fluctuation, rainfall, groundwater draft, ANN.

Adaptability of four cassava (Manihot esculenta crantz) cultivars in swampy inland valley ecology

Cassava is a popular dry season crop grown to utilize residual soil moisture in inland valleys. Trials to evaluate growth rates of four cultivars (TMS 4(2) 1425, TMS 91/02324, TMS 91/02327 and Isunikankiyan) were conducted along the toposequence in a 4 x 4 Latin square design. Effects of toposequence position, site, year and their interactions as well as of cultivar were significant for Leaf area index (LAI), net assimilation rate (NAR), crop growth rate (CGR), tuberous root bulking rate (TRBR), relative growth rate (RGR) and root yield. LAI, NAR, CGR, TRBR and RGR correlated positively with yield. TMS 91/02324 and TMS 91/02327 with the highest growth indices produced the highest yields. The deep water table site at Alabata had the highest growth indices and yield in valley bottom and the lowest in the fringe, while the shallow water table site at Ibadan recorded higher yield and growth indices in the fringe than the other positions. The shallowest water table depths at Ibadan and Alabata were and below mound surface in valley bottom and fringe, respectively. Valley fringe at Ibadan and valley bottom at Alabata had similar water table depth and they produced the highest growth indices and yield. Shallow water table of below mound surface reduced LAI, TRBR, CGR, RGR and yield, but increased NAR. Drought stress and high radiation, temperature andevaporation reduced yield and growth indices, while well distributed rainfall increased them. Cassava cultivars with high root yields in swampy inland valley are early maturing and maintain high LAI, TRBR, CGR, RGR and NAR under excess soil moisture and drought stress. Keywords: Growth indices, Cassava cultivars, Root yield, Groundwater table depth, Inland valley ecology, Drought stress

Detection of sub-surface waterlogging using Terra-1 MODIS data

Waterlogging due to rising ground watertable, being a sub-surface phenomenon, is not amenable to detection by optical remote sensing. Microwave and thermal sensor data have, however, shown some promise in the detection of sub-surface waterlogging. The present study was taken up to evaluate the potential of near-IR, short-wave IR (SWIR) and thermal-IR data from Moderate Resolution Imaging Spectrometer (MODIS) aboard Terra-1 acquired during day-and-night time postmonsoon data for detection of sub-surface waterlogging. The approach involves retrieval of day-and-night land surface temperature (LST), generation of normalized difference of channel-2 and 6 (ND26); 2 and 7 (ND27); ground truth collection involving concurrent ground water table observations to satellite date of pass, thresholding of normalized differences (NDs) and correlating the NDs with depth of ground water table. Amongst various spectral indices, day and night-time LST difference (DLST) and night-time LST have been found to correlate well with the incidence of waterlogging (water table depth < 2m), followed by normalized difference of band-2 (841–876 nm) and band-7 (2105–2155 nm). The sensitivity of threshold limits for these indices was maximum for DLST followed by ND26 and ND27. Poor accuracy of detecting sub-surface waterlogging with thermal bands during day time is attributed to the non-corresponding of the time of Terra MODIS data acquisitions with thermal maxima of the terrain. Though the ND27 gave better accuracy to detect subsurface waterlogging, it is very sensitive to threshold limits.