Environmental flow assessment of Kayan River: managing sustainability indicator of hydropower project

Nowadays, constructing a new hydropower plant is one of the most attractive solutions to overcome energy requirements. The Kayan Hydroelectric, built in the Kayan River, is projected to generate electricity of nine hundred megawatts. However, the dams have to be managed appropriately since alteration of river discharge will have a significant impact on the environment. This paper proposes an environmental flow assessment as an appropriate indicator to manage sustainability. Three environmental flow assessment methods were used: Flow Duration Curve Analysis (FDCA), Tennant method, and Building Block method. The environmental flow pattern was used as a benchmark to evaluate whether the operation rule of the dams fulfilled the sustainable requirement, particularly on the hydrological pattern of the river. Regarding the Tennant and FDCA method, the minimum discharge that has to be maintained for the minimum environmental flow of the river is about twenty-five cms (corresponds to ten percent of AFF) and thirty-five cms, respectively. Meanwhile, the Building block method informs a range of discharge from a hundred cms to twenty thousand cms during the flood. The environmental flow should be managed to guarantee that the river’s ecosystem and carrying capacity can be preserved.

Implementing an Operational Framework to Develop a Streamflow Duration Assessment Method: A Case Study from the Arid West United States

Streamflow duration information underpins many management decisions. However, hydrologic data are rarely available where needed. Rapid streamflow duration assessment methods (SDAMs) classify reaches based on indicators that are measured in a single brief visit. We evaluated a proposed framework for developing SDAMs to develop an SDAM for the Arid West United States that can classify reaches as perennial, intermittent, or ephemeral. We identified 41 candidate biological, geomorphological, and hydrological indicators of streamflow duration in a literature review, evaluated them for a number of desirable criteria (e.g., defensibility and consistency), and measured 21 of them at 89 reaches with known flow durations. We selected metrics for the SDAM based on their ability to discriminate among flow duration classes in analyses of variance, as well as their importance in a random forest model to predict streamflow duration. This approach resulted in a “beta” SDAM that uses five biological indicators. It could discriminate between ephemeral and non-ephemeral reaches with 81% accuracy, but only 56% accuracy when distinguishing 3 classes. A final method will be developed following expanded data collection. This Arid West study demonstrates the effectiveness of our approach and paves the way for more efficient development of scientifically informed SDAMs.

Simulation and Optimization of Airport Rainwater Drainage System at Different Control Measures

The impervious area of the airport is high, which leads to the deterioration of the water environment and frequent waterlogging disasters. The construction of sponge airport has become an important and arduous task in the new era of civil aviation design industry in China. In order to compare the effects of different control measures at different scenarios, take the airport along China's southeast coast as an example, three scenarios were designed in this study (Scenario 1: no LID facilities and other measures; Scenario 2: two pump stations were setting; Scenario 3: both LID facilities and pump stations). Three simulation models under LID facilities and other measures were developed using SWMM with return period of 5a. The simulation results at different scenarios were compared, the number and the best opening scheme of pumps for each reservoir are finally obtained. The results of Scenario 3 show that the full-flow duration of nodes in the study area is greatly shortened. The decrease of full-flow duration of J1, J2 and J3 was 1.2, 0.8 and 0.5 hours respectively, with reduction rates of 40%, 53.3% and 28.6% respectively. The rainfall peak flows both the first and the second were reduced in this scenario, and the reduction rates were 10.68% and 12.78% respectively. However, the reduction effect of the third peak is poor with the further increase of rainfall intensity. The reduction rate of the total inflow and peak flow of rainwater buckets and permeable pavement is better than that of vegetative swale. The results of this study can provide the reference for the design of sponge airport and the airport flood control management.

Simulation and Optimization of Airport Rainwater Drainage System At Different Control Strategies

The impervious area of the airport is high, which leads to the deterioration of the water environment and frequent waterlogging disasters. The construction of sponge airport has become an important and arduous task in the new era of civil aviation design industry in China. In order to compare the effects of different control strategies at different scenarios, take the airport along China's southeast coast as an example, three scenarios were designed in this study (Scenario 1: no LID facilities and other measures; Scenario 2: two pump stations were setting; Scenario 3: both LID facilities and pump stations). Three simulation models under LID facilities and other measures were developed using SWMM with return period of 5a. The simulation results at different scenarios were compared, the number and the best opening scheme of pumps for each reservoir are finally obtained. The results of Scenario 3 show that the full-flow duration of nodes in the study area is greatly shortened. The decrease of full-flow duration of J1, J2 and J3 was 1.2, 0.8 and 0.5 hours respectively, with reduction rates of 40%, 53.3% and 28.6% respectively. The rainfall peak flows both the first and the second were reduced in this scenario, and the reduction rates were 10.68% and 12.78% respectively. However, the reduction effect of the third peak is poor with the further increase of rainfall intensity. The reduction rate of the total inflow and peak flow of rainwater buckets and permeable pavement is better than that of vegetative swale. The results of this study can provide the reference for the design of sponge airport and the airport flood control management.

Establishing a water resources assessment system for Eswatini (Swaziland) incorporating data and modelling uncertainty

The uneven distribution of water resources availability globally puts pressure on environmental and human or socio-economic systems and has complex implications for the interactions within these systems. The natural environment and water resources are increasingly threatened by development, and water management crises are still occurring. This is exacerbated by the lack of accurate and adequate information on these systems. In Eswatini, for example, the pressure on the available water resources is mounting due to increasing water demand for irrigation while information about natural hydrological conditions and levels of water resources developments are uncertain. In addition, the practical application of hydrological models for water resources assessments that incorporate uncertainty in Eswatini has yet to be realised. The aim of the study, therefore, was to develop a water resource assessment system that is based on both observed and simulated information and that includes uncertainty. This study focusses on a regional water resource assessment using an uncertainty version of the Pitman monthly rainfall-runoff model whose outputs are constrained by six indices of natural hydrological response (i.e., mean monthly runoff, mean monthly groundwater recharge, Q10, Q50 and Q90 percentage points of the flow duration curve and % time of zero flows) for each of the 122 sub-basins of the transboundary catchments of Eswatini. A 2-step uncertainty modelling approach was tested, validated and then applied to all the sub-basins of Eswatini. The first step of the model run establishes behavioural, but uncertain model parameter ranges for natural incremental sub-basin hydrological responses and the model is typically run 100 000 times for each sub-basin. The parameter space that defines the uncertainty in parameter estimation is sampled based on simple Monte Carlo approach. The second step links all the sub-basin outputs and allows for water use parameters to be incorporated, where necessary, in order to generate cumulative sub-basin outflows. The results from the constraint index analysis have proved to be useful in constraining the model outputs. Generally, the behavioural model outputs produced realistic uncertainty estimates as well as acceptable simulations based on the assessment of the flow duration curves. The modelling results indicated that there is some degree of uncertainty that cannot be easily accounted for due to some identified data issues. The results also showed that there is still a possibility to improve the simulations provided such issues are resolved. The issues about the simulation of stream flow that were detected are mainly related to availability of data to estimate water use parameters. Another challenge in setting up the model was associated with establishing constraints that match the parameters for natural hydrological conditions for specific sub-basins and maintaining consistency in the adjustment of the model output constraints for other sub-basins. In an attempt to overcome this problem, the study recommends additional hydrological response constraints to be used with the Pitman model. Another main recommendation relates to the strong cooperation of relevant catchment management authorities and stakeholders including scientists in order to make information more available to users. The new hydrological insight is derived from the analysis of hydrological indices which highlighted the regional variations in hydrological processes and sub-basin response across the transboundary basins of Eswatini. The adopted modelling approach provides further insight into all the uncertainties associated with quantifying the available water resources of the country. The study has provided further understanding of the spatial variability of the hydrological response and existing development impacts than was previously available. It is envisaged that these new insights will provide an improved basis for future water management in Eswatini.

Pengaruh Tutupan Lahan terhadap Base Flow Index DAS Way Seputih Provinsi Lampung

Tujuan penelitian ini adalah menganalisis nilai Base Flow Index (BFI) dan debit baseflow DAS Way Seputih; menganalisis nilai Curve Number (CN) composite DAS Way Seputih tahun 2005, 2009, dan 2011; serta menganalisis pengaruh perubahan tutupan lahan terhadap baseflow DAS Way Seputih. Penentuan baseflow tahun 1973-2006 menggunakan Metode RDF (Recursive Digital Filter) terbaik berdasarkan uji kinerja, yaitu Root Mean Square Error (RMSE), R2, dan grafik FDC (Flow Duration Curv) di antara metode Lyne&Hollick, EWMA, Chapman Algorithm, dan Nathan and McMahon. Kemudian Metode RDF terbaik ini dibandingkan dengan Model SCS-CN (Soil Conservation Sevice Curv Number) untuk menentukan baseflow dan BFI tahun 2005, 2009, dan 2011 berdasarkan uji kinerja. BFI DAS Way Seputih tahun 2005, 2009, dan 2011 berturut-turut adalah 0,8178; 0,54225; dan 0,649502. Untuk nilai CN I composite, CN II composite, dan CN III composite tahun 2005 berturut-turut adalah 63,9191; 79,8869; dan 80,1315. Nilai CN I composite, CN II composite, dan CN III composite tahun 2009 berturut-turut adalah 42,7834; 60,8427; dan 83,6676. Sedangkan Nilai CN I composite, CN II composite, dan CN III composite tahun 2011 berturut-turut adalah 66,4066; 81,9460; dan 94,5943. Nilai BFI dipengaruhi oleh debit baseflow dan debit sungai. Debit sungai dipengaruhi oleh curah hujan, sedangkan debit baseflow dipengaruhi oleh perubahan luas tiap jenis tutupan lahan.