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Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
In dry clay soils, the rainfall is intercepted and absorbed in depth by cracks, known as synclasis, formed by clay shrinkage due to water losses for evaporation. Infiltrated rain may saturate the clay beyond the limit of plasticity, so that in hilly areas upper soil levels may easily creep, causing slope instability. Rainwash, sliding screes, and landslides supply rivers with fragments of various grain sizes, which increase the momentum of the runoff, and the erosive effects of its collision against the rough surface of riverbed and banks. Sheet erosion is the transport of loosened soil particles by overland flow. Interflow mainly erodes fine particles, depending on the intergranular water head, which eventually may cause even soil liquefaction during earthquakes (Committee on Earthquake Engineers and Commission on Engineering and Technical Systems, 1985).
Impact of Urbanization on Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
As shown in Figure 5.4, SWMM provides an integrated environment for editing study area input data, running hydrologic, hydraulic, and water quality simulations, and viewing the results in a variety of formats. SWMM calculates the runoff (overland flow) from the urban area by accounting for various hydrologic processes, which include (EPA, 2017):Runoff reduction via green infrastructure practices.Time-varying rainfall (precipitation) and evaporation of standing surface water.Snow accumulation and melting.Rainfall interception from depression storage.Infiltration of rainfall into unsaturated soil layers.Percolation of infiltrated water into groundwater layers.Interflow between groundwater and the drainage system.Nonlinear reservoir routing of overland flow.
Runoff
Published in Sandeep Samantaray, Abinash Sahoo, Dillip K. Ghose, Watershed Management and Applications of AI, 2021
Sandeep Samantaray, Abinash Sahoo, Dillip K. Ghose
In hydrology, runoff is the excess water from rain (precipitation) coming from land surface over the earth's surface to main channel. It includes water travelling over land surface and through channels for reaching a stream and interflow as well (Sun and Peng, 2019; Gao et al., 2020; Goudarzi et al., 2020; Samantaray and Sahoo, 2020a; Samantaray and Sahoo, 2020b). Interflow refers to water which penetrates the surface of soil and travels by gravitational force towards a stream (above central groundwater level at all times) and ultimately drains to the channel. Runoff also includes groundwater flow or subsurface flow (Chow, 1964). It is a part of infiltrated water that infiltrates downwards to ground and laterally flows for emerging in depressions and rivers and joins surface flow. Total runoff is equal to total precipitation minus losses due to storage (as in temporary ponds), evapotranspiration (loss to atmosphere from plant leaves and soil surfaces), and other abstractions.
Comparing single and multi-objective hydrologic model calibration considering reservoir inflow and streamflow observations
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2019
James Bomhof, Bryan A. Tolson, Nicholas Kouwen
WATFLOOD models the hydrologic cycle for the watershed. Precipitation and temperatures are input as forcing data into the model. Snow accumulation and melt are based on an index temperature algorithm based on the National Weather Service Flow Forecast System (Anderson 1973). Interception and subsequent evaporation of rainfall are controlled by a model developed by Linsley et al. (1949) based on maximum canopy storage. Evaporation is controlled by a modified Hargreaves algorithm (Hargreaves and Samani 1985) and requires the daily temperature ranges. The Philips formula (1954) governs infiltration. Interflow, or flow from the upper soil layer, is controlled by a Darcian based equation where the hydraulic gradient is computed from the land surface slope. Overland flow, if any, is based on the Manning formula with the same hydraulic gradient as the interflow. Groundwater is recharged from the upper zone using a parameterized linear equation and baseflow is released from groundwater using an exponential storage-discharge equation. If fens or substantial bank storages are present, all upland flow is passed into a separate bank storage and discharged or replenished from the stream using the Dupuis-Forchheimer discharge formula as described by Bear (1979). Lake storage is accounted for by simple storage-discharge relations based on power or polynomial functions. Finally, surface flows are routed through each grid cell using a storage routing technique based on Manning’s equation.
Identification of critical watershed using hydrological model and drought indices: a case study of upper Girna, Maharashtra, India
Published in ISH Journal of Hydraulic Engineering, 2021
The observed inflow of Girna dam has a decreasing trend (Ramkar and Yadav 2018). The reasons for the decrease in the water level of Girna dam is an abstraction of water from surface or ground, construction of small dams, and diversion of water for irrigation purpose (GoM 2015).Thus, it is necessary to find the SDI value for each watershed above to Girna dam. In concern to this, the SDI is calculated for the runoff generated from the SWAT model at watershed or sub-basin scale. The analysis period of 30 years from 1981 to 2010 was taken into account. Two extreme and four severe drought occurrences were observed in these 30 years. The extreme drought episode having a maximum negative value for the common year 2000–2001 for each watershed was selected to carry out spatial distribution of SDI at the watershed scale. The spatial distribution of SDI is shown in Figure 11. The IDW method is used to make this map by taking the centre of gravity points of each watershed. In between the year 2000–2001 the western part of the study area faces the moderate drought while southeast part encountered with extreme type drought. The middle northern region of the study area suffered the severe type of drought with some pockets suffering extreme drought present in the study area, i.e., watershed 3 and 7. The watershed numbers 15, 20, 23 and 24 faced extreme drought condition in the years 2000 and 2001. The major reason of hydrological drought present in the study area is the geology and soil associated with it. The study area is having amygdaloidal hard rock basalt with lineament. This phenomenon is accountable for the interflow through cracks and increases groundwater potential of deep aquifer and decreases the chances of streamflow return. Moreover the water demand of the study area is close to or higher as compared to the water available in the Girna dam (Poyil and Misra 2015). Thus, a greater use of rainwater harvesting structures, equal transfer policy, wastewater reuse and desalinated water in the study area will result in the conservation of water reducing the chances of the occurrence of streamflow drought (Patil 2015; Udmale et al. 2016; Tamaddun et al. 2018).