Rainfall-Runoff modelling

Rain simulation experiments utilising a transportable spray irrigation installation for the assessment of runoff behaviour on typical runoff contributing areas in alpine catchments have been carried out at the Department of Natural Hazards of the BFW in Austria and the LfU for more than three decades. These investigations usually have been combined with investigations on site characteristics, e.g. information on vegetation and soil. Data from more than 700 single rain simulation experiments have been stored in a joint database and analysed in detail.
The first product emerging from these analyses has been the simple “Code of Practice for assessment of surface runoff coefficients in convective torrential rain (version 1.0)” - presented in 2004. It has evolved into a basic means for the derivation of surface runoff coefficient maps, which are needed to calculate peak runoff and runoff amount in torrent catchment areas in case of extreme precipitation, e.g. the recurrent design event.
Within the last eight years target-oriented spray irrigation experiments have been continued and new insights into runoff development have been gained. This information and suggestions from practitioners have been incorporated into this present version of the “code of practice (version 2.0)”.
This manual comprises advice for the assessment of surface runoff coefficients and surface roughness as well as a function for the calculation of initial abstraction on runoff contributing areas in alpine catchments. A short list of data on velocities of shallow interflow in Central European geological substrates and pictures illustrating typical field situations bring the manual down to a round figure.

Key words: Cultivation, runoff coefficient, runoff coefficient map, runoff contributing area, runoff delay, shallow interflow, simulation of torrential rain, surface roughness, surface runoff

Probable maximum precipitation (PMP) is widely used by hydrologists for appraisal of probable maximum flood (PMF) used for soil and water conservation structures, and design of dam spillways. The estimation of design storm for example depends on availability of rainfall quantities and their durations. Daily maximum multiannual series are one of the main inputs for design streamflow calculation. The study generated annual series of Daily maximum rainfall for fourty four stations by using statical approach such as Normal distribution, Log-Normal Distribution, Pearson type III distribution and Gumbel's Distribution .Results reveals that among the different statical approaches Log-Normal distribution fits the best compared to others. Isohyetal Maps of study area at different frequency are produced by using GIS tools, the maximum intensity varies from 2.5 mm/hr to 628 mm/hr.

Olive trees native to the Middle East and Iraqi Kurdistan region, it can survive severe ecosystems including sandy and rocky soils with high calcite content and extreme temperature fluctuations between -7°C up to +45°C giving yields even with minimum rainfall requirement. Results show that olive is currently grown in a very limited area of less than 250 ha, under drip irrigation system, which mostly depended on supply of water from ground water in Sulaymaniyah governorate. In contrast, 90% of the world’s olive is dependent on precipitation. In addition, olive can grow and survive minimum rainfall of 300 mm and give satisfactory yields with rainfall of 500 mm without irrigation. The majority of olive fields were established in best fertile agricultural lands. Meanwhile, the
aforementioned lands are rich with montmorillonite, which swells when it is moisten and shrinks when it is dry. Therefore, resulting in deep cracks in the soil which causes breaking down of the roots and weakening of the trees. The total rainfall in Sulaymaniyah governorate, during the last 72 years (1941 to 2013), had dropped down below the minimum rainfall requirements for olive growing. This makes olive trees suitable and economic for utilizing sandy and rocky soils. Therefore, olive has a great role in the re-vegetation process of severe ecosystems and should be included in any program of renewing the Kurdistan region forest and developing green area which encourage the tourism in the Region and helping in beautifying and purifying the atmosphere from the poisonous
gases.

Effective impervious area (EIA), or the portion of total impervious area (TIA) that is hydraulically connected to the storm sewer system, is an important parameter in determining actual urban runoff. EIA has implications in watershed hydrology, water quality, environment, and ecosystem services. The overall goal of this study is to evaluate the application of successive weighted least square (WLS) method to urban catchments with different sizes and various hydrologic conditions to determine EIA fraction. Other objectives are to develop insights on the data selection issues, EIA fraction, EIA/TIA ratio, and runoff source area patterns in urban catchments. The successive WLS method is applied to 50 urban catchments with different sizes from less than 1 ha to more than 2000 ha in Minnesota, Wisconsin, Texas, USA as well as Europe, Canada and Australia. The average, median, and standard deviation of EIA fractions for the 42 catchments with residential land uses are found to be 0.222, 0.200, and 0.113, respectively. These values for the EIA/TIA ratio in the same 42 catchments are 0.50, 0.48, and 0.21, respectively. While the EIA/TIA results indicate the importance of EIA, 95% prediction interval of the mean EIA/TIA is found to be 0.07 to 0.93, which shows that using an average value for this ratio in each land use to determine EIA from TIA in ungauged urban watersheds can be misleading. The successive WLS method was robust and is recommended for determining EIA in gauged urban catchments.

During recent years, Geographic Information Systems (GIS) as a powerful tool have had a tremendous impact on research techniques in the realm of geography and spatial analysis. The integrative ability of GIS to capture, store, manipulate, analyze, manage, and finally present all types of geographical spatial data, has drawn many attentions to it. Water Resources Engineering as a interdisciplinary field requires modeling and analyzing data with different spatial resolutions. Therefore, GIS could definitely be utilized as a suitable tool for solving water resources problems from local to global scale. This paper tries to present the larger scheme of the benefits for the applications of GIS in water resources and hydrological modeling in particular. Certainly, within the few pages ahead only the surface is scratched and a more thorough and comprehensive review requires more time and effort. The fundamental reason for the need of integrating GIS and hydrological modeling is briefly discussed and different tools are introduced. Also, various examples of GIS application are presented to create a better understanding. Case studies such as the Wadi Madoneh Basin in Jordan, Kuronagi River in Japan and San Antonio River Basin in Central Texas, USA, are presented. The good agreement between the results from a fairly simple GIS model and observations in cases such as Kuronagi River and Wadi Madoneh is indicating a promising future for GIS application in hydrological modeling. Finally, the benefits of GIS utilization in the field are discussed and summarized.

The study of rain statistics, including average and extreme conditions, plays a significant role in predicting link availability and in calculating required tradeoff margins for the designing of a ground to space RF link. In this paper the cumulative distribution of average rainfall measured for 15 years is used in order to obtain probabilities of exceedance of rainfall rates using cumulative time statistics and empirical models for the Indian subcontinent. The results are compared with the rain rates extracted from the ITU-R model for the locations under study. The calculated rainfall rates suggest significant variances in the climatic features such as probability of heavy rain and number of rainy days in a year. The analysis shows that the ITU-R model underestimates the rainfall intensity rates by 32.6%, 26.2% and 40.7%, 19% at higher and lower percentage of time when compared with measured rain rate data from Indian Metrological department. It is shown that the discrepancy between the empirical model and ITU-R model at higher percentage of time results in a 15 to 5 dB difference in predicted signal attenuation depending on the region, percentage of time and frequency. Adaptive Power Control is proposed as a means to improve the link availability during period of higher intensity rainfall.

Many rivers in Nepal are either ungauged or poorly gauged due to extreme complex terrains, monsoon climate and lack of technical and financial supports. In this context the role of hydrological model is extremely useful. In practical applications, hydrological models are relatively simple to implement and reasonably accurate. The present study concerns about simulating the flow of the Marshyangdi river basin and validate with the gauge station within the studied basin area. Furthermore, estimation and analysis of discharges for each subbasins of Marshyangdi river basin has be performed in this study. The HEC-HMS 4.3 hydrologic model (Developed by US Hydrologic Engineering Center was used to calibrate (from 2003-2007) and validate (from 2008-2012) the Marshyangdi river basin. The main data required as input includes rainfall, DEM (digital elevation model) soil, land use and metrological for model. After having data, HEC-HMS model are operated. The main output from model is discharge at the outlet of the catchment. Finally, the output is compared with the observed discharge at selected gauging of the basin. It is crucial to properly calibrate and validate models to give confidence to model users in prediction of stream flow. The SCS curve number method, SCS unit hydrograph method, constant monthly method and Muskingum methods are the best fit performed methods of the hydrological processes of infiltration loss, direct runoff transformation, base flow and routing part respectively. The model performance was tested for the river basin during calibration and validation period, The Nash-Sutcliff (E NS) and Coefficient of determination (R 2) used to evaluate the performance of the model. The results obtained are satisfactory and accepted for simulation of runoff. The SCS curve number method, SCS unit hydrograph method, constant monthly method and Muskingum methods are the best fit performed methods of the hydrological processes of infiltration loss, direct runoff transformation, base flow and routing part respectively. Thus, this study shows that HEC-HMS hydrological model can be used to model the upper Marshyangdi river basin for better assessment and prediction of simulation of the hydrological responses. The study recommends further studies which incorporate the land use change of the basin in the model.

Resumen: La determinación de la escorrentía superficial es primordial para resolver problemas vinculados a los excedentes hídricos y el posterior diseño de estructuras hidráulicas o para la adopción de medidas no estructurales. Existen antecedentes de acoplamiento de los procesos de escurrimiento superficial e infiltración. En general, los estudios de acoplamiento buscan determinar el escurrimiento superficial mejorando la determinación de los procesos de infiltración. El acoplamiento de ambos procesos es conveniente como una mejora que considera más adecuadamente la interacción de los procesos de infiltración y escorrentía. En este trabajo se resuelven las ecuaciones de onda cinemática para el escurrimiento superficial y la ecuación de Richards en forma conjunta y secuencial para eventos de larga duración. Para ello se aplicó el programa HEC-1 para el cálculo de la escorrentía superficial y NETRAIN 3.0 que permite resolver la ecuación de Richards unidimensionalmente. El programa desarrollado (NETRAIN 3.0) permite calcular la infiltración considerando las propiedades hidráulicas de los suelos. Fue realizado específicamente para poder unirse al programa HEC-1 y permitir calcular la escorrentía, considerando la precipitación efectiva obtenida de descontar las pérdidas iniciales y la infiltración, aplicando la ecuación de Richards. NETRAIN 3.0 permite modelar períodos continuos de humedecimiento y secado y períodos sin precipitación, lo que permite calcular la lluvia efectiva evitándose así el uso de métodos aproximados como el de la humedad antecedente. Palabras clave: escorrentía, flujo no saturado, infiltración, modelos de infiltración. Abstract: The determination of surface runoff is essential for the solution of problems linked to flooding and the subsequent design of hydraulic structures or the adoption of non-structural actions. There are precedents of the coupling of surface runoff and infiltration processes. In general, coupling studies aim at quantifying surface runoff, improving the determination of infiltration processes. The coupling of both processes is convenient as an improvement that more appropriately considers the interaction of the infiltration and runoff processes. This work jointly and sequentially solves the kinematic wave equations for surface runoff and Richards' equation for long-term events. For this, HEC-1 program was applied for the calculation of surface runoff as well as NETRAIN 3.0, which allows solving Richards' equation in one dimension. The program developed (NETRAIN 3.0) allows the calculation of infiltration considering the hydraulic properties of the soils. NETRAIN 3.0 was specifically carried out to be combined with HEC-1 and to allow the calculation of runoff, considering the effective rainfall obtained from deducting the initial losses and infiltration, applying Richards' equation. NETRAIN 3.0 allows modeling continuous moistening and drying periods and periods without rainfall, which permits calculating effective rainfall, thus avoiding the use of approximate methods such as those using the previous humidity.

This paper presents a method of obtaining the right PMF hydrograph for a Kenyir catchment,
which, in the case of a dam safety study, is the hydrological step, of determining the input
hydrograph. Design floods for Kenyir dam is based on the probable maximum flood (PMF)
which  results  from  the  probable  maximum  precipitation  (PMP)  using  hydrometeorological
method involving maximisation and transposition of historic storms. The PMF is defined as
the flood that may be expected from the most severe combination of critical meteorological
and hydrologic conditions. The method used to determine the PMF is deterministic approach,
which  uses  Probable  Maximum  Precipitation  (PMP)  as  the  meteorological  input.  The
deterministic method of calculation of PMF consists of the transformation of the PMP with a
rainfall-runoff  deterministic  model  into  a  runoff  hydrograph.  For  the  hydrologic  modeling
studies the new version of HEC-HMS hydrologic modeling software released in April 2006 by
US Army Corps of Engineers is used. The inputs of the model in determination of PMF are the
sub-basin physical parameters such as area and the length of the stream, reach parameters,
reservoir parameters and meteorological parameters which are Type I-PMP, Pseudo Mersing
Storm  and  Type  II-PMP,  Nested  Bell  Shaped.  As  a  result  of  model  application  studies,
infiltration loss and baseflow parameters of each subbasin are calibrated. Both type of PMP
gives  a  PMF  value  which is below the designed value 21,400m
3
/s. The Type II-PMP gives
higher value of PMF which is 18,889.7m
3
/s compared to Type 1-PMP which is 16,051.1m
3
/s.
Therefore,  the  hydrological  review  indicated  that  the  dam  is  safely  design  under  PMF
condition with adequate capacity of the spillway to discharge the PMF to the downstream in
the event of extreme rainfall.

Water flow and water quality changes in surface water bodies due to climate change is a major problem worldwide, typically in river ecosystems. To address these issues, proper monitoring of river flow variations and water quality is necessary, but daily monitoring and data collection is greatly time consuming and costly. Therefore, a study was done with the objectives to calibrate and validate the HEC-HMS 3.5 and HEC-RAS 4.1.0 models to simulate flow variation and water quality variations respectively in Nillambe Oya, Sri Lanka. The development of such models are a significant requirement in the present scientific world to predict river flow and water quality variations as an adaptation for the climate change. The HEC-HMS 3.5 model was used to generate flow which is needed for HEC-RAS 4.1.0. Daily flow data for five years (from October 1991 to September 1996) were used to calibrate the HEC-HMS 3.5 model and another set of daily flow data for five years (from October 1994 to September 1999) were used to validate the model. HEC-RAS 4.1.0 model was calibrated using water quality data collected and analyzed in five days. The validity of the calibrated model was evaluated using water quality data collected in the other four days. The calibrated and validated HEC-HMS 3.5 model reliably predicted the flow in Nillambe Oya. The calibrated and validated HEC-RAS 4.1.0 model simulated Dissolved Oxygen (DO), Biological Oxygen Demand (BOD) and Nitrate Nitrogen (NO 3-N) splendidly. Orthophosphates was also predicted reliably by the model, but the simulation of organic Phosphorus was not that sensible.