Infiltration Tests Research Articles

Detailed Geophysical Mapping and Hydrogeological Characterisation of the Subsurface for Optimal Placement of Infiltration-Based Sustainable Urban Drainage Systems

The continuous growth of cities in combination with future climate changes present urban planners with significant challenges, as traditional urban sewer systems are typically designed for the present climate. An easy and economically feasible way to mitigate this is to introduce a Sustainable Urban Drainage System (SUDS) in the urban area. However, the lack of knowledge about the geological and hydrogeological setting hampers the use of SUDS. In this study, 1315 ha of high-density electromagnetic (DUALEM-421S) data, detailed lithological soil descriptions of 614 boreholes, 153 infiltration tests and 250 in situ vane tests from 32 different sites in the Central Denmark Region were utilised to find quantitative and qualitative regional relationships between the resistivity and the lithology, the percolation rates and the undrained shear strength of cohesive soils at a depth of 1 meter below ground surface (m bgs). The qualitative tests enable a translation from resistivity to lithology as well as a translation from lithology to percolation rates with moderate to high certainty. The regional cut-off value separating sand-dominated deposits from clay-dominated deposits is found to be between 80 to 100 Ωm. The regional median percolation rates for sand and clay till is found to be 9.9 × 10−5 m/s and 2.6 × 10−5 m/s, respectively. The quantitative results derived from a simple linear regression analysis of resistivity and percolation rates and resistivity and undrained shear strength of cohesive soils are found to have a very weak relationship on a regional scale implying that in reality no meaningful relationships can be established. The regional qualitative results have been tested on a case study area. The case study illustrates that site-specific investigations are necessary when using geophysical mapping to directly estimate lithology, percolation rates and undrained shear strength of cohesive soils due to the differences in soil properties and the surrounding environment from site to site. This study further illustrates that geophysical mapping in combination with lithological descriptions, infiltration tests and groundwater levels yield the basis for the construction of detailed planning maps showing the most suitable locations for infiltration. These maps provide valuable information for city planners about which areas may preclude the establishment of infiltration-based SUDS.

Kinetic and gas-phase study of the chemical vapor deposition of silicon carbide from C2H3SiCl3/H2

The chemical vapor deposition (CVD) of silicon carbide from vinyltrichlorosilane (VTS) was studied to identify a range of conditions leading to pure crystalline SiC. The deposition rate was recorded to evidence the various deposition regimes. Gas phase, elemental analyses and infiltration tests were also performed. Three distinct chemical reaction regimes were identified. In CVD conditions, carbon is co-deposited at low temperature while VTS is only partially decomposed. In infiltration conditions, the composition switches to pure SiC inside the porous substrate because of a depletion of reactive hydrocarbon species. Competing heterogeneous reactions are responsible for a hysteresis versus temperature, in both deposition rate and composition of the deposit. The high temperature domain is the most suitable to deposit pure crystalline SiC in CVD conditions. Hydrogen dilution strongly accelerates the homogeneous decomposition of VTS as compared to argon. Assumptions on the reaction mechanism were proposed describing the chemistry of this precursor.

Woody plant encroachment enhances soil infiltrability of a semiarid karst savanna

Semiarid karst landscapes are often the source areas for regionally important groundwater supplies. Like savannas across the globe, these landscapes are experiencing an increase in woody plant cover—often referred to as woody plant encroachment. Although this phenomenon is commonly viewed as leading to increased transpiration and reduced groundwater recharge, this may not be true of all ecosystems. For example, in the Edwards Plateau region of central Texas—where the underlying geology is karst—dramatic increases in baseflows have occurred concurrently with the expansion of woody plants. It has been suggested that in this context woody plants, especially juniper (Juniperus spp.), are partially responsible for boosting recharge by improving soil infiltrability, but this hypothesis has not been systematically evaluated. Our study examined the effects of an important encroaching shrub (Redberry juniper) on soil infiltrability in the Edwards Plateau. We carried out a large number of infiltration tests to determine soil infiltrability and used a dye tracer followed by soil profile excavation to estimate the potential for deep percolation. Tests were performed at increasing distances under juniper shrubs of five size classes, ranging from young seedlings to mature shrubs. We found that in soils underlying shrubs, infiltrability was quintupled and percolation depth almost tripled compared with soils in intercanopy zones. Surprisingly, shrub size was not a significant factor. Even the soils beneath the smallest shrubs had much higher infiltrability than intercanopy soils, showing that these woody plants modify soil properties at very early stages. We also found that both infiltrability and percolation depth gradually increased with proximity to the trunk and showed a strong correlation with litter thickness. Our results provide support for the hypothesis that in semiarid karst landscapes, woody plant encroachment—especially the invasion of juniper—can play an important role in enhancing groundwater recharge by improving the soil infiltrability.

Phosphorus recovery from soil through phosphorus extraction and retention on material: A comparison between batch extraction-retention and column percolation

Phosphorus (P) recovery from wastewater and soil is important for preventing the depletion of P resources; however, a method for recovering P from soil has not yet been developed. We designed and tested systems to recover P from excavated and in situ soil. P extraction from soil using citric acid, EDTA, and water is combined with P retention by calcium (Ca)- and magnesium (Mg)-containing material in both the batch extraction-retention and column percolation approach. In the batch extraction-retention test, Ca hydroxide retained more P than the other materials at 0.38–0.76 mg g−1, and the P was retained as Ca phosphate-like minerals. The amount of P retained by materials using chelating solutions was higher than with water, regardless of the material. The amount of P in the Ca-containing materials after the column percolation test was higher than in the Mg-containing materials, with the exception of Ca carbonate. In the column percolation test, the percentage of P recovery from the available P in the soil was 4.9% and 3.5% using Ca hydroxide and Ca oxide with water, respectively, and the application of chelating solutions did not improve P recovery. In the batch extraction-retention test, the percentage of P recovery using Ca hydroxide and Ca oxide with water was the same as that obtained by the column percolation test; however, the use of chelating solutions could improve the P retention to more than 11% and 7%, respectively. These results demonstrate that more than 10% and 5% of the available P in the soil could be recovered using Ca hydroxide in the batch extraction-retention test with citric acid and EDTA solutions and the column percolation test with water, respectively. The P-retained material may be used as a source for the production of chemical fertilizer.

Water infiltration in a cracked soil considering effect of drying-wetting cycles

Infiltration is of great concern in many fields like hydrology, agriculture as well as geotechnical and geological engineering. This study aims to investigate water infiltration in a cracked soil. Infiltration tests were conducted on compacted soil samples with different cracking degrees by drying to various water contents. Three drying-wetting cycles were applied. Experimental results show that no desiccation cracks are observed in the first drying process while cracks initiate and propagate in the second and third drying processes. Different from the infiltration curve of the non-cracked soil sample consisting of two distinct stages, that of the cracked soil consists of three distinct stages, representing constant, rapid reduction and gradual reduction in infiltration rate, respectively. A modified equation is proposed to describe the infiltration behavior of a cracked soil considering the prehealing time of cracks. Furthermore, it is found that for the tested soil, 4% of surface crack ratio is a critical value. When surface crack ratio is smaller than the critical value, its influence on infiltration capacity is insignificant. Afterwards, the infiltration capacity increases dramatically with increasing surface crack ratio. Based on this observation, a piecewise function is proposed to characterize the relationship between the normalized infiltration capacity of cracked soil and surface crack ratio. Infiltration capacity also increases with decreasing initial water content and increasing number of drying-wetting cycles. In terms of steady final infiltration rate, it increases with increasing initial water content as well as increasing number of drying-wetting cycles, but is not affected by desiccation cracking.

Experimental study on infiltration of unsaturated soil and solution of permeability coefficient

During the unsaturated infiltration, water content, infiltration rate, infiltration amount and other physical quantities are all related to the water supply approaches and intensities. In order to study the change of water migration and the permeability coefficient in vertical infiltration of one-dimensional soil column with different infiltration conditions, this paper designs an experimental device for a one-dimensional soil column infiltration model. Three sets of infiltration tests with different intensities were carried out in two ways: artificial rainfall infiltration and ponding infiltration. The results show that the infiltration under the conditions of rainfall infiltration and ponding infiltration presents a similar trend. The infiltration of ponding in the initial stage of infiltration has greater fluctuations than the infiltration of rainfall, but after the latter stabilizes, the infiltration capacity of ponding infiltration and rainfall infiltration tends to be the same. Finally, on the basis of the theory of soil water energy state and the law of conservation of energy, a new method for solving the permeability coefficient of unsaturated soil under free infiltration is obtained.

Determination of Sorptivity, Infiltration Rate and Hydraulic Conductivity of Loamy Sand using Tension Infiltrometer and Double-Ring Infiltrometer

This study was conducted to assess the effectiveness and accuracy of tension infiltrometer (TI) over double ring infiltrometer (DI) for determining infiltration rate (I) of loamy sand. Sorptivity (S), infiltration rate and hydraulic conductivity (K) are soil properties that govern the rate of entry of water into the soil and its movement within the soil. The ease and accurate measurement of these properties depend on the instruments used. DI operates by ponding water and could be affected by preferential water flow during infiltration test which could not be avoided especially on a fertile soil. DI and TI at water potentials of -0.02, -0.04, -0.05 and -0.06 m were used to determine infiltration rate of the soil. The mean values of sorptivity for DI and TI at water potentials of -0.02, -0.04, -0.05 and -0.06 m were 847.02, 63.50, 33.15, 29.90 and 19.46 mm/h1/2, respectively. Mean values of infiltration rates for DI and TI at -0.02, -0.04, -0.05 and -0.06 m water potentials were 471.26, 176.84, 73.73, 71.32 and 37.73 mm/h, respectively. Mean values of hydraulic conductivity for DI and TI at -0.02, -0.04, -0.05 and -0.06 m were 344.45, 22.42, 18.61and 16.83 mm/h, respectively. DI required 100-150 litres for the infiltration test, difficult where water is very scarce and gave higher values of infiltration rate. TI saved water (2-3 litres), controlled preferential water flow and values of S, I and K were within the range obtained by other researchers. TI is more effective for measuring hydraulic properties soil than DI.Keywords:Double ring infiltrometer, tension infiltrometer, sorptivity, infiltration rate, hydraulic conductivity

Estimation of hydraulic conductivity in fractured crystalline aquifers using remote sensing and field data analyses: An example from Wadi Nasab area, South Sinai, Egypt

Fractured crystalline aquifer is considered as the main source of water supply in most of the arid and semi-arid regions. Fractures play an essential role as pathways through which groundwater flows from high catchments to supply the productive wells in lowlands. The hydraulic conductivity measurements for highly fractured crystalline aquifers are a must for optimal management of groundwater extraction from these aquifers. The current work aims at estimating the hydraulic conductivity of the crystalline aquifer by using an unconventional approach based entirely on the processing of remotely-sensed lineament data and field observations. Extracted lineaments at four sites near the productive wells along Wadi Nasab area (WNA) were traced from Landsat (ETM+7) and other ancillary geological data by using image processing and GIS tools. Hence, four discrete fracture networks (DFN) were designed and practiced for the selected test sites to model the groundwater flow through the fracture system in order to estimate the hydraulic conductivity of the investigated crystalline aquifer. The achieved results indicated that the hydraulic conductivity of fractured basement aquifer of WNA varied between 2.3 × 10−7 and 6.1 × 10−7 m/s. The estimated hydraulic conductivity values are close to the values of previous field infiltration tests in the nearby area at Sinai. The previously estimated infiltration rates (expressing the vertical hydraulic conductivity) on the fractured crystalline outcrops ranged between 2.6 × 10−6 and 6.5 × 10−7 m/s, which are concordant with achieved results. Moreover, the achieved values match the previously published values of hydraulic conductivity for similar crystalline aquifers around the world, reflecting the high validity of the used unconventional, low-cost approach to estimate the hydraulic conductivity of fractured crystalline aquifers. The designed approach can be potentially practiced on similar basins in Sinai peninsula and other comparable basins having similar geological and climatic environments around the world.

The impermeability effect of soil air on the ponding infiltration experiment of soil column

The agricultural flood irrigation in Jingyang South Platform, Shaanxi Province caused the rise of groundwater level, which induced a large number of loess landslides. The study of water movement in unsaturated loess under irrigation is the premise of revealing the mechanism of loess landslide. In this paper, the changes of matric suction, volume moisture content and air pressure with time at different depths of unsaturated undisturbed loess are measured by indoor soil column water infiltration test. Air pressure at each point of the soil rises to about 98 Pa in a short time after the test beginning, and keeps small fluctuation up and down during the test. At the end of the experiment, the air pressure at each point of the soil returns to zero in a short time after the upper water accumulation is eliminated. During the test, the change of infiltration rate has a significant corresponding relationship with the exhaust phenomenon at the top of the soil column, and the air resistance significantly reduces the infiltration rate of water.

Impact of initial structural heterogeneity on long-term swelling behavior of MX80 bentonite pellet/powder mixtures

To better understand results of SEALEX in situ tests carried out at Tournemire Underground Research Laboratory, the hydromechanical behavior of a pellet/powder MX80 bentonite mixtures prepared at a dry density of 1.49 Mg/m3 were investigated by means of microfocus X-ray computed tomography (μ-CT) observations and laboratory small scale infiltration tests. Radial and axial swelling pressures as well as relative humidity were monitored while wetting. Two configurations were considered: for the first, a pellet/powder mixture was prepared following a specific protocol to minimize initial structural heterogeneity; the second one was specially designed to study a strong heterogeneous mixture distribution. μ-CT observations performed on the two samples during hydration revealed an apparently homogeneous sample for the first mixture after 100 days of hydration. For the second specimen, several voids were still observed after 40 days of hydration. A comparison was made between the in situ and mock-up tests. It was observed that the evolutions of radial and axial swelling pressures depend on the initial heterogeneous distribution of the mixture. This heterogeneity is due to the different dry density values at the vicinity of the different sensors. The final values of axial swelling pressures were different for both configurations for the same global dry density.

Hydraulic and sorption performances of soil amended with calcium-magnesium composite powder against natural arsenic contamination

Excavated soils and rocks, containing toxic metals and/or metalloids from geogenic sources, are usually generated in huge volumes at construction sites. And the post-excavation leaching of these toxic metals and/or metalloids with low concentrations, but higher than the environmental standards, is a major environmental concern. A sorption layer method was developed as a cost-effective countermeasure for treating and reusing such excavated soils and rocks. The method utilizes a permeable soil layer, with sorption capacity at the bottom of the embankment, to retain the chemicals of concern that have dissolved in the leachate. Clean host soil, amended with toxic metal-immobilizing agents, is often used as the sorption layer material to strengthen the sorption performance. This study examined the feasibility of applying decomposed granite soil, amended with calcium-magnesium (Ca-Mg) composite powder, as the sorption layer material against the natural contamination of arsenic (As). The hydraulic and sorption performances, along with the effect of the mix proportions and curing periods, were evaluated through batch sorption tests, hydraulic conductivity tests, and up-flow column percolation tests. The results showed that the sorption performance increased by 15 times when using an additive content of 5% Ca-Mg and that hydraulic conductivity was maintained at around 1 × 10−6 m/s. Neither the hydraulic nor the sorption performance was strongly affected by curing periods up to 28 days. The sorption performance increased with the addition of the Ca-Mg agent of up to 5% in the batch sorption tests. The permeable hydraulic property, with an improved sorption capacity due to the soil-agent mixture, indicated that it is a promising material for use with the sorption layer method for treating huge amounts of soils with low levels of contamination.

Applicability of wetting front advancing method in the sand to silty clay soils

The unsaturated hydraulic conductivity function is one of the keys to solve unsaturated seepage issues, and it is difficult to be obtained via the laboratory test considering the time involved. In this study, a series of laboratory tests, include capillary rise test and downward infiltration test, were conducted to obtain the unsaturated hydraulic conductivity function of six kinds of soils varies from sand to silty clay by using the wetting front advancing method. The similarities and differences between instantaneous profile method and wetting front advancing method were discussed. The interpretation of data, demand details and the aspect that notice in test process, and application of the capillary rise test and downward infiltration test were summarized and analyzed. The demerits and its countermeasures for the method were given.

The internal erosion process and effects of undisturbed loess due to water infiltration

Internal erosion is a complex phenomenon that is one of the main risk factors to soil destruction. Its occurrence is mainly due to water infiltration and can cause slope instability. “Karst soil” is a type of loess with special soil and water sensitivity that makes it prone to landsliding. The processes of internal erosion include transport erosion and chemical dissolution, which strongly effect loess structure and strength. To reveal the internal processes and effects of the loess due to water infiltration, field investigations and indoor tests, including infiltration tests, undrained triaxial tests, particle analysis, chemical analysis, and scanning electron microscopy (SEM), were conducted. The results show that (1) the fine particles (clay and silt) and chemicals can move within the matrix of the macro-pores under seepage flow. The physical internal erosion is mainly due to fine particle migration out of the water and clay and silt particles, and the sample column settlement was 3.3 cm with a settlement ratio of 16.5%, which results in changes to the soil skeleton, increasing the porosity and infiltration rate of loess. (2) Chemical dissolution is also an important internal erosion process in loess, especially cations of Na, Mg, Ca, and K and anions of Cl, SO4, and CO3, which are mainly lost due to dissolution and flow out of with water and clay particles, resulting in altered physical characteristics of the soil. (3) Soil particles’ mitigation and chemical dissolution change the loess structure, leading to skeletal destruction and decreased peak strength and residual strength of the infiltrated sample to 7.75% and 8.13%, respectively. During internal erosion, physical fine particle migration and chemical dissolution are important for loess stability and loess slope susceptible to failure during water infiltration.

USE OF DIFFERENT INFILTROMETERS TO ASSESS ENVIRONMENTAL DAMAGE CAUSED BY DIFFERENT LAND USES

The present work had an objective to compare the stable infiltration rate obtained by infiltrometers with reduced dimensions and varied forms in different land uses. The infiltration tests were carried out in areas planted with cowpea, crotalaria, pigeon pea and millet, as crops previous corn planting, and managed with no-tillage, minimum tillage and conventional tillage and native forest area. In order to compare and analyze the results of the stable infiltration rates obtained between the alternative infiltrometers and the considered standard, the criteria involving the standard error of estimation (EPE), the standard error of estimation adjusted (EPEa), the standard error of estimation adjusted by origin (EPEao) and coefficients of adjustments of the linear equations with their respective determination coefficients (R2) were used. It was verified that the double-ring reduced, single-ring and double square infiltrometers provided a water saving of 57.06%, 66.19% and 38.54% respectively, relative to the standard. The alternative infiltrometers overestimated the stable infiltration rate in relation to the standard. The single-ring infiltrometer obtained a stable infiltration rate correction equation that showed results very close to the standard and the best statistical indices of stable infiltration rate results were obtained by the reduced double-ring infiltrometer.

Electrical resistivity tomography monitoring of two managed aquifer recharge ponds in the alluvial aquifer of the Llobregat River (Barcelona, Spain)

ABSTRACTOver the past 20 years, there has been growing interest in the use of the subsurface for water storage using shallow ponds, where water is infiltrated to the subsurface and subsequently groundwater is recovered from pumping wells. This scheme is designed as a surface‐managed aquifer recharge. Llobregat artificial recharge ponds are managed aquifer recharge systems located in alluvial aquifers near Barcelona, with strong significance for water supply to the city. The recharge ponds have shown low infiltration rates since the beginning (e.g., Ca n'Albareda) and a significant decrease after some months (e.g., Sant Vicenç). Consequently, different methodologies were designed for monitoring the systems and evaluating the effectiveness of the selected areas and maintenance procedures. For this purpose, we combined the use of electrical resistivity tomography with standard hydrogeological methodologies, including water table monitoring from piezometers and infiltration tests. The combination of direct and indirect methods have allowed us to improve the diagnosis of the subsurface involved in the managed recharge system. The electrical resistivity tomography technique has shown to be a cost‐effective and high‐resolution tool, flexible and well adaptable for surveying at different scales without disturbing the recharge process. As a consequence, we demonstrate the usefulness of electrical resistivity tomography imaging to unveil hydrogeological heterogeneities and monitoring infiltration, the effect of clogging and clean‐up processes in surface‐managed aquifer recharge projects.

Ponded infiltration and spatial–temporal prediction of the water content of silty mudstone

Ponded infiltration is very common in silty mudstone and has a great influence on the stability of related slopes, road cuttings, and tunnels. This paper aims to examine the infiltration performance of silty mudstone and predict the distribution of its water content under ponded conditions. By infiltration tests, the infiltration rate (i), cumulative infiltration (I), and their variations with the infiltration time (t) were obtained. Afterward, the variation of water content (w) with t and depth (s) was analyzed. The results show that the i value decreases with the increase in the degree of saturation, and the I value increases first significantly and then slightly during water infiltration. The entire w–t curve at any s is S-shaped, while the w–s curve at any t is full or half inverse-S-shaped. In addition, an equation was developed for the w–s prediction based on the simplified Gompertz curve model, and it was further extended to the spatial–temporal prediction model of water content. The evaluation results demonstrate that the spatial–temporal prediction model has high accuracy and reliability. The prediction model also indicates that the range of the infiltration-affected zone increases and the rate of increase slows down during water infiltration.

Multi-criteria performance evaluation of a glass panel system using full-scale experimental data

In order to better evaluate the lifetime performance of glass panel facade systems, this study firstly proposes to conduct a full-scale wind resistance, air/water infiltration, and seismic resistance tests. Two specimens were designed, constructed, and tested for this purpose. A fatigue process is also applied to one of the manufactured systems in addition to a standard test procedure. Secondly, data acquired from the experimental part of this work have been used in a multi-criteria performance evaluation process to determine the performance levels of each of the specimens. In the evaluation process, a total of 10 different criteria and 2 alternatives are identified for decision making. Performance indicator data obtained from the detailed calculations using the AHP (Analytic Hierarchy Process), COPRAS (Complex Proportional Assessment) and TOPSIS (The Technique for Order of Preference by Similarity to Ideal Solution) methods are then utilized during the numerical assessment process. The ‘criticality level’ is defined within the evaluation process and it indicates the percent (%) values of the obtained performance indicators. As a result of the performance evaluations, the AHP and TOPSIS methods gave similar results and could be selected as the preferred methods for the evaluation of such experimental data. Results obtained from the AHP and TOPSIS methods are consistent and easy to interpret when compared to the COPRAS method. Furthermore, in this work, the most critical criterion is found to be the frontal deflections.

Modelling soil water infiltration variability using scaling

One of the most substantial and crucial parameters for irrigation in agriculture is water infiltration into the soil. Given the variability of soil properties, the infiltration characteristics also vary. The present study aims to model soil water infiltration using scaling. In the present research, a new approach for scaling the infiltration equation was developed and evaluated for 22 infiltration tests. In the new method, the scaling factor ( F s ) for each equation equals the depth of infiltrated water after the specified time ( t s ) in the reference infiltration equation. This new method was applied to Philip's equation and was compared with previous Philip equation scaling methods such as sorptivity coefficient ( α s ), transmissivity coefficient ( α A ), the optimal factor obtained using the least squares error ( α o p t ), geometric, arithmetic and harmonic mean α s and α A . Results showed that scaling using F s has the best match with measured data (R2 = 0.99, MBE = 0.0006 and RMSE = 0.001) when compared to other Philip equation scaling methods. Among scaling techniques from the literature, F s had the highest correlation with α o p t (R2 = 0.96). The proposed method applied to the Kostiakov–Lewis infiltration equation was also evaluated. The results of the scaling of the Kostiakov–Lewis equation showed that to use reference curve is optional and each of the infiltration curves can be used as reference curve. As a whole, the results of the proposed method showed that the cumulative infiltration curve can be obtained using minimum infiltration-time measurement data.

Estimation of the soil hydraulic properties from field data by solving an inverse problem

Estimating unsaturated soil hydraulic properties to predict water dynamics through a vertical soil profile under the effects of irrigation, drainage and evapotranspiration is imperative for managing soils in the arid regions. The aim of this work was to determine the soil water retention curve and the hydraulic permeability function of a bare soil profile in a Tunisian oasis threatened by salinization. The developed model combines a numerical inversion of the unsaturated flow equation with the BOBYQA optimisation algorithm. The direct model solved the Richards equation using a cell-centred finite difference model. Hydraulic properties were described by van Genuchten-Mualem models. Input data for the inverse problem are the infiltration flow, soil water contents and pressure heads measured during ponded infiltration and internal drainage tests. Numerical simulations of these two tests were performed considering a homogeneous single-layer soil profile but a better fitting between measured and simulated water contents was obtained when the soil profile was divided into five sub-layers. The hysteresis phenomenon was highlighted from the soil water retention and the relative permeability curves corresponding to the ponded infiltration and internal drainage tests.

A unified approach for hydrological modeling of arid catchments for flood hazards assessment: case study of wadi Itwad, southwest of Saudi Arabia

A unified and systematic approach for hydrological modeling is presented for assessing flood hazards in arid and semi-arid regions with wadi Itwad as a case study. The approach consists of the following steps: (1) estimation of the design storm duration, (2) estimation of the design rainfall depth, (3) development of the design storm hyetograph, (4) setup of the watershed hydrological system, (5) infiltration tests for estimate of soil characteristics, (6) land use and land cover analysis for curve number estimation, (7) how to incorporate dams (if any) and their reservoir characteristics for reservoir routing analysis, and (8) performing hydrological modeling under different scenarios, namely: lumped with and without the effect of dams and routed scenarios. An emphasis is made on the comparison between the SCS unit hydrograph and the unit hydrograph (UH) estimated for stream flow data. The UH method produces hydrographs that are typical of arid regions. It is characterized by a steep rising limb with a short time to peak, a rapid recession to zero base flow, and less flood volume due to transmission losses. The scenarios show that the lumped case overdesigns the protection schemes, while the lumped central basin with detention dams storing the flood water completely leads to underdesign in the downstream area. The routed scenario is more realistic, since it considers the detention dams with an overflow. The runoff volume (66.6 MCM) of the 10-year return period of the routed scenario is in the order of magnitude within the observed historical data (50 to 100 MCM) reported in the literature. The study concludes that the proposed approach is robust and takes into account the Saudi arid environment while performing flood risk assessment in KSA.