Stage-Based Flood Inundation Mapping

New methods allow the direct computation of flood inundation maps from lidar data, independently of discharge estimates, hydraulic analysis, or defined cross sections. One method projects the interpolated profile of measured flood levels onto surrounding topography, creating a smooth inundation surface that is entirely based on data and geometrical relationships. A second method computes inundation maps for any simple function that relates the water surface to the elevation of the channel bottom, exploiting their known, sub-parallel character. A final method theoretically combines the elevation of the channel bottom and the upstream catchment area for points along the thalweg, all defined by lidar data. The conceptual simplicity and realism of these maps facilitate data-based planning.

Livestock and Small-Scale Irrigation Scheme Interactions as a Key Source for Sedimentation during the Irrigation Season: Four Case Studies from South-West Shoa, Ethiopia

Small-scale irrigation (SSI) development can play a major role in Ethiopia’s economic development, but sedimentation is a major threat to its sustainability. The focus of the dominant discourse around the sedimentation of SSI schemes lies in upstream catchment protection during the rainy season, neglecting both protection against erosion through overland flow along the margins of the canal network and sedimentation caused by livestock disturbances. Remedies against the latter causes of sedimentation during the irrigation season have been ineffective due to erroneous assumptions regarding its cause. This study aimed to identify the sources and extent of sedimentation in SSI schemes. The accumulated sediment in the canal pre-irrigation season was measured from four SSI schemes and suspended sediment samples during irrigation season were collected from one SSI scheme. The accumulated sediment in the canal pre-irrigation season was measured from four SSI and suspended sediment samples during irrigation season were collected from one SSI scheme. The extent of sedimentation in the canals during the pre-irrigation season in relation to canal capacity was 100% of lined and unlined canals in abandoned, 68% in a lined, and 84% unlined canals in heavily sedimented and 38% in a lined and 46% of unlined canals lightly sedimented schemes. Livestock interactions with the SSI schemes were found to be the major sediment source before and during the irrigation, hence, attention should be given to integrating livestock as a part of the system.

Occurrence and distribution of Organochlorine Pesticide Residues in Water and Sediments of Earthen Fish Ponds in South Western Kenya

Persistent organochlorine residues in the environment are a threat to ecological health of aquatic organisms and pose a health risk to both animals and human consumers. Organochlorine pesticides were determined in water and sediments collected during wet and dry season from selected riverine and earthen fish pond sites in high altitude catchment areas within Kuja River (Kenya) between August 2016–May, 2017. Analysis of DDT and metabolites, Hexachlorocyclohexanes (HCHs) isomers and cyclodienes using a gas chromatograph (GC), and electron capture detector (ECD), confirmed using GC - Mass Spectrometry (MS). Mean (± Standard error) results of DDTs, cyclodienes and HCHs in pond waters were:- below detection level (BDL) to 0.27±0.03µg/L, BDL to 0.11±0.00µg/L, and 4.39±1.01µg/L respectively; and BDL to 0.23±0.01µg/L, 1.20±0.005µg/L, and 1.71±0.02µg/L in river water respectively. Sediment mean OCPs contents were significantly (p<0.05) higher for Dieldrin (3.043±0.43µg/kg), Endrin (2.56±0.460µg/kg), Heptachlor (3.61±0.02µg/kg) DDT (2.97±1.32µg/kg), Endosulfan (6.31.27±1.051µg/kg), Methoxychlor (2.15±1.641µg/kg) and Lindane (2.96±1.32µg/kg), respectively. A longitudinal spatial distribution pattern was noted for both water and sediment OCPs contents, demonstrating that cyclodienes are predominant contaminants in point and non-point sources in water courses. The study recommends continuous monitoring of OCPs in upstream catchment areas for informed management and policy decisions on pesticide use. Keywords: Kuja-Migori River; Organic contaminants; Organochlorine Pesticide.

Hydropower potential assessment made easy via the unit geo-hydro-energy index

&lt;p&gt;The design of hydropower works typically follows a top-down approach, starting from a macroscopic screening of the broader region of interest, to select promising clusters for hydroelectric exploitation, based on easily retrievable information. Manual approaches are very laborious and may fail to detect sites of significant hydropower potential. In order to facilitate this kind of studies, we provide a novel geomorphological approach to assess the hydropower potential across river networks. The method is based on the discretization of the stream network into segments of equal length, thus providing a background layer of head differences between potential abstraction and power production sites. Next, at each abstraction point, we estimate the so-called unit geo-hydro-energy index (UGHE), which is a key concept of our approach. UGHE is defined as the ratio of annual potential energy divided by the upstream catchment area, the head difference, and the unit annual runoff of the catchment, which is set equal to 1000 mm. The method is further expanded, to estimate the actual hydropotential, if spatially distributed runoff data are available. All analyses are automatized by taking advantage of the high-level interpreted programming language Python and the open-source QGIS tool. The proposed framework is demonstrated at the regional scale, involving the siting of run-of-river hydroelectric works in the Peneios river basin.&lt;/p&gt;

Regionalization of Reservoir regulation parameters using physiographic and climatological predictors

&lt;p&gt;Present regional and global scale hydrology has to account for man-made reservoirs that impart significant regulation signature into the downstream streamflow regime. Optimization of domains with large number of reservoirs would incur multitude of reservoir regulation parameters. Such parameter-set-per-reservoir approach not only results in excessive computational costs but also, by principle, lacks effective constraining of the parameter space. We propose an approach to derive single set of parameters for all the reservoirs and lakes in the modelling domain. The hypothesis is that reservoir regulation parameters can be regionalized using physiography and climatology at lakes and their catchments.&lt;br&gt;&lt;br&gt;To test this hypothesis, we setup a modeling domain for the S&amp;#227;o Francisco basin of Northeast Brazil in the mesoscale hydrological model (mHM, www.ufz.de/mhm). The domain consists of climatology ranging from tropical (As) to semi-arid (BSh) and reservoirs with catchment area varying from less than 500 km&lt;sup&gt;2&lt;/sup&gt; to greater than 500,000 km&lt;sup&gt;2&lt;/sup&gt;. We carried out correlation analysis between selected physiographical and climatological predictors and the reservoir parameters of the multiscale lake module, mLM, of the mHM model (https://presentations.copernicus.org/EGU2020/EGU2020-6047_presentation.pdf). For an instance, the reservoir rule curves in mLM are estimated based on inflow and position of water level. The predictors here are inflow and water level which are normalized using catchment area and the shape of the reservoir, respectively. Similarly, the timing and shape parameters of rule curves were plotted against the climatological characteristics of the upstream catchment. The preliminary results reveal significant trends between the mLM parameters and the normalized predictors. These mathematical relationships, better known as transfer functions, can now be used to generate a single global reservoir parameter set.&lt;/p&gt;&lt;p&gt;The demonstrated hypothesis helps to optimize regulated hydrology using a single parameter set, irrespective of size, location and inherent climatology of reservoirs involved. This is inline with the pre-existing paradigm of multiscale parameter regionalization (MPR) of mHM. The findings contribute to the contemporary effort of hydrological modeling society towards improved global scale hydrological modeling.&lt;/p&gt;

The Changes of Runoff with DEM Resolution Variations

Currently there has been a research gap in providing sufficient and reliable data for the estimation of surface runoff from ungauged catchment in Batang Kuranji watershed, City of Padang, West Sumatera, Indonesia. The need for such data arose from the fact that land cover changes occur rapidly in the past 20 years, and flash flood and river degradation have been experienced at an alarming scale. However, due to lack of discharge data from upstream catchment, modelling catchment response to the effect of land use changes is hampered. Field measurement is difficult due to accessibility to river tributaries in the upstream catchment. Therefore, the use of digital satellite images and digital elevation model is studied with various DEM (Digital Elevation Model) resolutions for the first time in this catchment. This catchment is situated from 95 to 1858 m above sea level with an annual rainfall of 3440 mm. This watershed is classified as steep with a watershed that has a slope of more than 40% reaching 37.01% of the entire Kuranji watershed area. This study used 30 m and 8 m DEM. Secondary data were gathered from satellite images such as MODIS (MODerate resolution Imaging Spectroradiometer) Land Use. Precipitation data were gathered from three rain gauging stations in or nearby the catchment. Stream geometry data were obtained from the Provincial Office for River Management. Annual discharge and 100-year discharge are calculated using rainfall data for the past 20 years. Runoff discharge was calculated using rational method and SCS (Soil Conservation Services) method. Overall, computed discharge decreases as DEM resolution decreases with percentage varies between 0.98% to 1.76%. The biggest difference between DEM of 30 m and 8 m was shown by the Rational method. However, the difference between years is inconsistent with methods used with no significant pattern. Using the rational method, the biggest difference was by 18.73 m3/s, making up 1.76%. With SCS-CN, however, the biggest difference was 14 m3/s or 1.32% and the smallest was 0.98%. Validation with field measurement suggests that the 8-m DEM varies only 0.16% with actual discharge. Therefore, in the Kuranji catchment, the SCS method coupled with 8-m DEM was found to be accurate for the estimation of surface runoff

Supraglacial and subglacial meltwater routing in Kongsfjord basin, Svalbard

&lt;p&gt;In tidewater glacier fjords, the amount, the spatial distribution, and the timing of meltwater entering the subglacial hydrological system play a key role in modulating ice flow dynamics, as well as in impacting adjacent marine ecosystems. This study aims to describe how meltwater journeys through the polythermal glaciers of Kongsfjord basin in Svalbard, Norway. Our methodology involves the use of a surface runoff timeseries (2003-2017) from a coupled surface-energy-balance-snow model forced by a regional climate model (HIRLAM). Using a program for flow pathways analysis in DEMs (TopoToolbox), we generate a map of surface meltwater streams and drainage catchment areas. Other supraglacial features such as melt lakes, moulins and crevasses are manually detected from satellite imagery. These serve as basis to create four different setups of water input to a subglacial drainage model (GlaDS): &lt;strong&gt;(1)&lt;/strong&gt; a spatially continuous input that equals the surface runoff, &lt;strong&gt;(2)&lt;/strong&gt; a discrete input where the total surface runoff over the whole Kongsfjord basin is equally distributed between moulins, &lt;strong&gt;(3)&lt;/strong&gt; a discrete input where upstream catchment areas are taken into account to weight the runoff drained into each moulin, and &lt;strong&gt;(4)&lt;/strong&gt; a hybrid configuration of (1) and (3) where in crevassed areas the input equals the surface runoff, while in non-crevasses areas moulins are fed by upstream catchment runoff. The subglacial drainage model, which allows for meltwater to flow through both an inefficient distributed network of linked cavities, and a more efficient channelized system, yields spatiotemporal information on basal water pressure, sheet discharge and channel discharge, as well as on channel location. Results for the four water input setups are compared, and we discuss the relevance of using a more realistic configuration of meltwater recharge when modeling hydrological systems underneath glaciers. Finally, based on our model outputs, we provide seasonal maps of Kongsfjord basin&amp;#8217;s subglacial hydrology that show the preferential flow path of basal water and through which glacier outlet meltwater is released into the fjord. &amp;#160;&lt;/p&gt;

Why water bodies of Iran have been dried up?

&lt;p&gt;The status of natural water bodies in terms of water quality and quantity can be considered a criterion for the environmental status of their upstream catchment. The presence of natural water bodies with good condition can be a sign proper of water resource management activities in the upstream catchment for sustainable development. Iran has been undergoing a rapid development process in recent decades. Nowadays, in most water bodies in Iran, the water level has been decreased and even disappeared in some cases. Lake Urmia is a well-known example of drying lakes in Iran. This study aims at identifying the main effective drivers in drying up of the main lakes in Iran.&lt;/p&gt;&lt;p&gt;Iran is a country with an approximate area of 1,648,000 km2 that has an arid and semi-arid climate with an average precipitation of 311 mm/year. The most important water bodies in Iran are Lake Urmia and Maharloo, Hoor-al-Azim and Gavkhuni Wetlands, and Gorgan Bay. This study focuses on the mentioned waterbodies and upstream catchment information.&lt;/p&gt;&lt;p&gt;At first, climate conditions and changes such as drought and changes in their properties are studied to find the answer to this question. Then, non-climatic factors and their changes such as urban/rural population changes, industrial growth, agricultural changes such as land area, crop yield, and the type of irrigation were studied. To achieve this purpose, the time series of the surface level of these five waterbodies was measured using satellite images. Then the time of significant changes in the time series of the surface level of each waterbody was determined using the Pettit test. As a result, the time interval for each waterbody was divided into a two-time span, before and after the change point. This created a time interval for climatic and non-climatic comparisons to identify effective factors.&lt;/p&gt;&lt;p&gt;The climatic data from the synoptic stations located in and around each waterbody catchment have been used to study the climatic conditions, and the sum of precipitation and mean temperature have been evaluated as the main climate parameters along with the SPIE drought index and characteristic changes. In order to evaluate effective non-climatic factors, changes in urban/rural population factors, agricultural land level, the number of agricultural products, and industrial units were used based on official statistics.&lt;/p&gt;&lt;p&gt;The results of this study indicate that the year of significant changes in the time series of lakes was between 1996 and 2001. Crop yield change growth was the main factor in the upstream catchment of all lakes as a result of changes in the irrigation patterns.&lt;/p&gt;

Influence of salinity gradient on Ni complexation by Fluorescent Dissolved Organic Matter (FDOM) and dispersal across estuaries in New Caledonia

&lt;p&gt;Dissolved organic matter (DOM) is ubiquitous in the environment. Its composition and properties depend on water type (freshwater, estuarine, brackish, marine) and are influenced by the geological nature (ultramafic, volcano-sedimentary, metamorphic) and occupancy (mangrove, forest, agriculture, urbanized) of the upstream catchment. Due to its capacity&amp;#160; to form complexes with dissolved trace metals, DOM can render them hardly available to living organisms, and thus limit their toxicity. Considering its capacity to be transported on large distances, DOM can significantly contribute to the dispersal of trace metals in aquatic ecosystems. In this study, we used 3D fluorescence spectroscopy to characterize the actual nature of FDOM (a fraction of DOM that shows specific fluorescence properties) across estuaries downstream of two contrasted catchments (ultramafic vs. volcano-sedimentary) in New Caledonia. In a first step, Excitation-Emission Matrix (EEM) were obtained on 0.2 &amp;#181;m filtered water samples and a parallel factor analysis (PARAFAC) allowed to identify the different FDOM components in the two catchments. These data indicated a dramatic decrease of all components as a function of increasing salinity, with a threshold value around 25 g/L whatever the catchment. This trend is considered to reflect an aggregation-flocculation behavior of FDOM across the salinity gradient of the studied estuaries. In a second step, fluorescence quenching experiments emphasized the complexing capacity of the different components toward dissolved Ni. FDOM might thus play a significant role on Ni dispersal in aquatic ecosystems through the formation of FDOM-Ni complexes. However, this dispersal capacity might be hampered&amp;#160;in estuaries due to the suspected aggregation-flocculation behavior of FDOM across the salinity gradient. Rather than the geological setting of the upstream catchment, salinity appears thus as the major driver of Ni dynamics across estuaries through FDOM-Ni complexes.&lt;/p&gt;