Drainage Direction Research Articles

An efficient assignment of drainage direction over flat surfaces in raster digital elevation models

In processing raster digital elevation models (DEMs) it is often necessary to assign drainage directions over flats—that is, over regions with no local elevation gradient. This paper presents an approach to drainage direction assignment which is not restricted by a flat's shape, number of outlets, or surrounding topography. Flow is modeled by superimposing a gradient away from higher terrain with a gradient towards lower terrain resulting in a drainage field exhibiting flow convergence, an improvement over methods which produce regions of parallel flow. This approach builds on previous work by Garbrecht and Martz (1997), but presents several important improvements. The improved algorithm guarantees that flats are only resolved if they have outlets. The algorithm does not require iterative application; a single pass is sufficient to resolve all flats. The algorithm presents a clear strategy for identifying flats and their boundaries. The algorithm is not susceptible to loss of floating-point precision. Furthermore, the algorithm is efficient, operating in O(N) time whereas the older algorithm operates in O(N3/2) time. In testing, the improved algorithm ran 6.5 times faster than the old for a 100×100 cell flat and 69 times faster for a 700×700 cell flat. In tests on actual DEMs, the improved algorithm finished its processing 38–110 times sooner while running on a single processor than a parallel implementation of the old algorithm did while running on 16 processors. The improved algorithm is an optimal, accurate, easy-to-implement drop-in replacement for the original. Pseudocode is provided in the paper and working source code is provided in the Supplemental Materials.

Facial Palsy and Nystagmus after Transvenous Embolization of a Carotid Cavernous Fistula

Facial Palsy and Nystagmus after Transvenous Embolization of a Carotid Cavernous Fistula

Application of 4D-CTA using 320-row area detector computed tomography on spinal arteriovenous fistulae: initial experience

Time-resolved computed tomography angiography (4D-CTA) using a 320-row area detector CT scanner has recently been applied in the evaluation of cranial vascular disorders. However, application of 4D-CTA to spinal vascular disorder evaluation has never before been described. The authors herein report their initial experience of 4D-CTA in the evaluation of spinal arteriovenous fistulas (AVFs) and compare this novel modality with other imaging modalities. Four consecutive patients with spinal AVF underwent time-resolved contrast-enhanced magnetic resonance angiography (trMRA), 4D-CTA, and selective catheter angiography (CA). In 4D-CTA, volume data was transformed into 3D volume-rendered images and maximum intensity projection. These images were also evaluated by time-resolved serial phases. Then, images of each modality were compared, focusing on the detection of perimedullary draining veins and the prediction of AVF location and drainage flow direction. All modalities successfully detected perimedullary draining veins in all cases. Location of the AVF was detected in all cases by CA. trMRA and 4D-CTA detected the AVF in three out of the four cases. With regard to flow direction, while 4D-CTA successfully depicted ascending or descending drainage flow in the spinal canal, CA failed to detect the flow direction in one case while trMRA failed in two cases. In the case with epidural AVF, 4D-CTA was the only technique to detect the flow direction of perimedullary drainage. Although this is only an initial experience of the application of 4D-CTA to spinal vascular diseases, 4D-CTA was capable of detecting the dynamic vascular flow of spinal AVFs. The authors believe that 4D-CTA can be a useful option in the evaluation of spinal AVFs.

Occlusion of a clival dural arteriovenous fistula using a novel approach through the foramen ovale

Dural arteriovenous fistulas (DAVFs) are abnormal connections between arteries and veins that are classified by location, morphology or direction of venous drainage. Treatment of DAVFs is undertaken in patients with...

Topographic analysis for the prairie pothole region of Western Canada

AbstractThe unique topography of the pothole region of the North American prairies creates challenges for properly determining basin contributing area. Numerous depressions or potholes within the landscape impound runoff. However, potholes can ‘fill‐spill’ resulting in surface water connections between the potholes. Surface water connectivity between potholes ultimately influences basin contributing area. Currently, automated methods, such as landscape analysis tools, treat depressions in the landscape as artifacts and simply fill the depressions to delineate a drainage basin. Using this method to calculate contributing area assumes that all surface storage has been satisfied (threshold) and the drainage basin will contribute 100% of its area for all runoff events. However, most runoff events in the prairie pothole region are pre‐threshold events that contribute only a portion of surface runoff to the outlet. These pre‐threshold events have surface storage that varies because of antecedent water levels and have a variable or dynamic potential to store further runoff in the basin. Government agencies have developed methodologies for determining pre‐threshold contributing areas, but these methodologies do not incorporate current technologies and, as a result, have limitations.We propose an automated method for determining contributing area that incorporates the fill‐spill of prairie potholes. The algorithm, which uses the D‐8 drainage direction method, automates a methodology for identifying and quantifying runoff contributing area. Any algorithm that determines pre‐threshold contributing area, must allow the DEM to be filled in an incremental manner. This will simulate increasing pond levels, and the resulting decrease in available storage in the basin, in response to runoff events. The SPILL algorithm is an iterative solution that increases the magnitude of input runoff events and records the decreasing change in available surface storage and the increase in contributing area until the storage threshold is reached and the contributing area reaches 100%. Through application of the algorithm on prairie pothole region basins, we test proposed conceptual curves that describe a hypothesized non‐linear relationship between decreasing potential storage in the landscape and contributing area. Results indicate that the proposed conceptual curves represent the relationship between potential surface storage and contributing area in the test basins very well. Copyright © 2012 John Wiley & Sons, Ltd.

Evolution of multilevel caves in the Sierra de Atapuerca (Burgos, Spain) and its relation to human occupation

The evolution of the Torcas cave system (Sierra de Atapuerca) is analysed in order to shed light on the formation of the Atapuerca archaeological sites and human occupation in the area, critical for identifying the paths of the first human dispersal into Europe. The geomorphological analysis of the endokarst system and the regional base levels has revealed a multilevel cave system, with drainage directions from south to north, where old karst springs fed the Pico River. Using morphological and topographic evidence we have correlated the fluvial terraces situated at relative heights of +84–80m and +78–70m above the Arlanzón River (main course), with the first and second cave levels, respectively, both of Early Pleistocene age. The fluvial levels T4 (+60–67m) and T5 (+50–54m) are linked with the third level (Early–Middle Pleistocene), which contains fluvial deposits probably related to terrace T6 (+44–46m). Progressive fluvial incision allowed humans to gain access to the cave system through several entrances from ~1.22Myr until the end of the Middle Pleistocene, when these cave entrances became filled, forming the most interesting hominid-bearing deposits in Europe.

New information on Neoproterozoic-Cambrian geology and the Triassic unconformity around Groby, southern Charnwood Forest, UK

Summary Detailed investigations utilizing borehole drilling, geophysical techniques and revision mapping have elucidated the geological evolution of southern Charnwood Forest. This study confirms that the South Charnwood Diorite was emplaced in latest Neoproterozoic times and has a broadly concordant intrusive contact with underlying volcaniclastic strata of the Charnian Supergroup. Following erosion that unroofed the diorite, an Early Cambrian marine transgression deposited an unconformable covering of Brand Group strata. In end-Silurian times, the region experienced orogenic compression and folding along a dominant NW–WNW tectonic grain. ‘Phase 1’ structures with these orientations include the Charnwood Anticline and a transecting, penetrative cleavage that is mainly developed in the stratiform Charnian rocks. Further manifestations of this deformation were systems of NW-trending faults, the most important of which is the Groby Reverse Fault. This complex structure is described here for the first time; it features a narrow tectonic slice of Brand Group rocks, which was thrown down into the South Charnwood Diorite. The courses of younger, ‘Phase 2’ faults are also revealed by the present study; they are orthogonal to, and thus offset the earlier NW structures. During Permian times, the area was stripped of its Carboniferous cover, resulting in a rugged pre-Triassic topography. This study has shown that the South Charnwood Diorite was eroded into low-lying, NW-elongated, steep-sided domes (bornhardts). It has also revealed the configuration of an associated palaeo-valley system, which suggests that regional tilting associated with development of the syn-Triassic Hinckley Basin to the south-west of Charnwood Forest may have influenced drainage directions before burial of the hill-range beneath desert sediments of the Mercia Mudstone Group.

Application of Multi-Directional Flow Consolidometer for a Constant Rate of Strain Consolidation Test Under Various Drainage Conditions

Abstract The use of vertical drains in the field demands sophisticated laboratory consolidation testing under various drainage conditions. In this study, a multi-directional flow consolidometer was developed for the constant rate of strain (CRS) consolidation test. This device provides variability in controlling the drainage direction (e.g., vertical, radially inward, radially outward) during K0 consolidation. For each drainage condition, relevant theories for interpreting the CRS testing data have been derived. Reconstituted kaolinite specimens were consolidated at a constant rate of 2.9%/h using the developed device with various drainage directions. The results showed consistent compression behavior, and the anisotropic coefficient of consolidation confirmed the applicability of the device in experiments involving in situ consolidation.

Modeling variable river flow velocity on continental scale: Current situation and climate change impacts in Europe

Summary This paper introduces an approach to route discharge with a variable river flow velocity based on the Manning–Strickler formula within large scale hydrological models. The approach has been developed for the global scale hydrological model WaterGAP and model results have been analyzed focusing on Europe. The goal was to find a method that is simple enough to derive the required parameters from globally available data while being sophisticated enough to deliver realistic flow velocity estimates for a large variety of environmental conditions. The river bed roughness (Manning’s n ) is approximated in a spatially explicit way based on topography, the location of urban population, and river sinuosity. The hydraulic radius is estimated from actual river discharge, and river bed slope is derived by combining a high resolution DEM, a 5 arc min drainage direction map, and river sinuosity. The modeled river flow velocity has been validated against data of US gauging stations. The representation of lateral transport has clearly been improved compared to the constant flow velocity applied in older model versions. The effect of incorporating variable flow velocities as compared to a constant flow velocity is largest on flood discharge, which generally increases in large rivers. The impact on monthly discharge hydrographs is marginal only. WaterGAP has been driven by three climate change projections for the 2050s to assess climate change impacts on flow velocity, and on the residence time of water in the European river system. Results indicate a decrease in residence times for Northern Europe and an increase for parts of the Mediterranean.

Groundwater hydrochemistry and soil pollution in a catchment affected by an abandoned lead–zinc mine: functioning of a diffuse pollution source

The importance of polluted alluvial soils as a potential diffuse source of heavy metals was investigated in a catchment of the Matylda stream affected by an abandoned lead and zinc ore mine in Upper Silesia, southern Poland. This was attempted by means of standard groundwater analyses performed together with measurements of Cd, Pb, Zn, Fe and Mn concentrations in soil and groundwater. The Matylda stream, receiving mine water, was converted in the 20th century into a straight channel directed in its middle reach over the valley bottom. This changed the drainage direction of the Matylda stream water. During mining operations, groundwater seepage, combined with surface drainage by shallow ditches caused pollution of sandy soils exceeding over 100 mg/kg of Cd, 24% of Zn and 4% of Pb at surface or subsurface soil horizons, and reaching at least 60 cm in depth. After mine closure in the 1970s, the network of ditches appears to be a source of Ca, Mg, chlorides, carbonates and nitrates, as indicated by the more or less regular increase of these major ion concentrations in groundwater down ditches. Whereas, the ditches are a sink rather than a source of zinc, cadmium and lead in permanently dry reaches, or transition zones in reaches with surface water flowing periodically. The metal concentrations and distribution in soil and groundwater suggest the slow mobilization of heavy metals stored in the valley bottom and the minor importance of soil as a diffuse source for surface water pollution.

The first report of bilateral retropharyngeal lymph node metastasis from papillary thyroid carcinoma and review of the literature

The sites of lymph node metastasis of papillary thyroid carcinomas are typically the paratracheal and jugular lymph nodes. On the other hand, metastasis to the retropharyngeal or parapharyngeal nodes from papillary thyroid carcinomas is very rare. During the last two decades, limited to cases with a histologically definite diagnosis by surgery, only 39 cases have been reported. All reported cases were unilateral retropharyngeal or parapharyngeal node metastasis except one metachronous bilateral case, and there were no reports of simultaneous bilateral cases within our literature review. We report three cases of retropharyngeal node metastasis from thyroid papillary carcinoma, including a case of bilateral nodal metastasis. Retropharyngeal node metastasis was successfully resected in all three patients by the transcervical approach. As pointed out in past reports, this report also suggests that prior neck dissection and/or metastasis to cervical lymph nodes might alter the direction of lymphatic drainage to the retrograde fashion, resulting in the unusual metastasis to the retropharyngeal lymph nodes, and there is a possibility of a bilateral pattern. Also, it is necessary to consider the possibility of metastasis from a papillary thyroid carcinoma in the differential diagnosis of lymph node swelling in the parapharyngeal space.

Preparation of the Stormwater Drainage Management Plan for Matara Municipal Council

Matara Municipal Council area had been experiencing stormwater drainage problems causing inconvenience to public, interruption to work and damage to property. Though the Matara Municipal Council (MMC) had carried out a project in 2001 to develop its drainage canals, there were many cases of flooding within its boundary limits. In order to achieve a suitable plan for stormwater drainage management, the present work carried out an analysis of the associated stormwater drainage system. Systematic field data collection activities were done to identify the flood problem of the area, and to capture sufficient details of terrain and drainages. GPS surveys were conducted to identify the road and drainage alignments. A main feature of the study was the conduct of a road drainage survey which among many other details captured drainage directions along and across the roads. This survey helped to rationally identify the undulations in the terrain to generate the digital terrain model for the generation of stream network and delineation of watersheds. The 1:10,000 elevation data supported by the field work information showed the capability to generate a representative topography for stormwater drainage assessments. Analysis also used a simple Geographic Information System to prioritize critical flood affected areas and enabled identification of critical watersheds for engineering interventions. The present canal system was evaluated with that generated by the model and several sections were identified for early drainage designs these locations were verified in the field. Present work identified that in the MMC area 42% of roads coincide with the stream network indicating a loading of street stormwater drains with runoff generation as a result of terrain changes affected at individual compounds. 164 identified flood locations were analysed with drainage directions and surrounding elevations supported by detailed engineering inspections at specific locations to provide short term solutions. The study made recommendations with respect to development plan approval procedures, preparation of a suitable stormwater drainage database and the need of guidelines for developers to mitigate stormwater drainage problems as part of the long term solutions.

The Usefulness of the Source Images of Magnetic Resonance Angiogram in the Carotid Cavernous Fistula

The cortical venous drainage from carotid-cavernous fistula (CCF) is associated with increased risk of intraparenchymal hemorrhage and may be the clue for the urgent indication of an endovascular treatment [1]. However it is difficult to infer direction of venous drainage from the clinical signs or symptoms of a patient with CCF. The source images of magnetic resonance angiogram (MRA) may useful to detect the direction and magnitude of the collateral circulations in the patient with carotid-cavernous fistula (CCF) [2]. A 68-year-old woman presented with progressive bilateral pulsatile tinnitus, headache and diplopia accompanied by swelling of both eyes, the right eye being more severely affected. She underwent surgical reconstruction of fractured facial bone 6 weeks ago due to car accident. From the 30th days after reconstruction, she suffered persistent progressive pulsatile tinnitus and periorbital pain. The MRA revealed marked leakage signals of arterial blood around cavernous sinus (Figure 1). The source image of MRA revealed increased transsellar collaterals, enlarged both sphenoparietal sinus and right side predominant elongated bilateral tortuous superior ophthalmic veins (Figure 2). Figure 1 The magnetic resonance angiogram (MRA) of the patient showed increased flow related signals around both cavernous sinuses. Figure 2 The source image of magnetic resonance angiogram (MRA) revealed increased transsellar collaterals (a, b), enlarged both inferior cerebral veins (C; arrow) and right side predominant elongated bilateral tortuous superior ophthalmic veins (c, d; arrow head). ...

Effect of Alpine karst on the hydrology of the Berchtesgadener Ache basin: a comprehensive summary of karst research in the Berchtesgaden Alps

The Berchtesgaden Alps are situated in the Northern Limestone Alps, characterized by individual mountain plateaus and ridges in close proximity to each other, intersected by valleys, with an altitudinal gradient of 2 100 meters. The limestone has been exposed to dissolution processes since the Cretaceous, leading to a massive karstified aquifer with a wide range of subsurface flow channels. There are hundreds of springs as groundwater recharge locations, feeding the seven rivers of the region that contribute to the Danube watershed. Several studies were conducted to examine the hydro-geological conditions and the resulting groundwater flow. This paper aims to evaluate and summarize research in the basin describing groundwater flow to identify the main drainage direction, travel times, spring dynamics and possible subsurface redistribution in the individual mountain ranges and the whole basin. To this end, we evaluate several tracer experiments, two isotope studies and a spring database. The tracer experiments are generating knowledge about flow directions in the individual mountain ranges, groundwater redistribution, water storage and mean travel times. Five experiments prove increased groundwater flow remaining within a valley and four experiments indicate groundwater redistribution through mountain ranges. The isotope studies indicate potential water storage in the Wimbach valley of an estimated 100 x 106 to 470 x 106 m3 and mean transit times of about four years. The analysis of the spring database focuses on locations and discharge classification. Overall, there are 289 springs recorded in the spring database, distributed from 600 to over 2 000 m altitude, with major springs at the northern base of the mountains Hochkalter, Watzmann and at the north shore of lake Königssee. The conclusion summarizes the effect of the karst aquifer on the hydrology of the region. The outlook introduces current research within the area and the distributed water balance modelling.

Completing Fragmentary River Networks via Induced terrain

Fragmentary river segments have to be reconnected before addressing various routing and tracking problems. Elevation determines drainage directions, so the partial heights available through LiDAR may provide useful hints on how the segments should be joined. However, it is not trivial how this information can be applied. This paper bridges this gap by proposing the induced structure approach, which first approximates a terrain compatible with those observations, and then derives a river network from that induced terrain. Since the network is derived from an induced terrain that honors the partial observations, we expect that the derived river network will enforce most restrictions imposed by the partial observations. This paper also provides specifics on the implementation. In the first step regarding terrain reconstruction, we find that the optimal scheme depends on the height sample distribution. If the samples are sparsely yet evenly distributed, natural neighbor interpolation with stream burning (NN-SB) is the most cost-effective. If the samples are offered only at the given river locations, the hydrology-aware version of Over determined Palladian Partial Differential Equation (HA-ODETLAP) should be used instead. In the second step concerning river derivation, we find it necessary to favor those given river locations. Otherwise they will be missed out. We set their respective initial water amounts to the critical accumulation level to ensure a river flows across them. In the subsequent branch thinning process, those locations are protected from being trimmed. We foresee applications of our solution framework in a few 2D and 3D network tracing problems with similar observation distribution, like dendrite network reconstruction.

The last erosional stage of the Molasse Basin and the Alps

We present a synoptic overview of the Miocene-present development of the northern Alpine foreland basin (Molasse Basin), with special attention to the pattern of surface erosion and sediment discharge in the Alps. Erosion of the Molasse Basin started at the same time that the rivers originating in the Central Alps were deflected toward the Bresse Graben, which formed part of the European Cenozoic rift system. This change in the drainage direction decreased the distance to the marine base level by approximately 1,000 km, which in turn decreased the average topographic elevation in the Molasse Basin by at least 200 m. Isostatic adjustment to erosional unloading required ca. 1,000 m of erosion to account for this inferred topographic lowering. A further inference is that the resulting increase in the sediment discharge at the Miocene–Pliocene boundary reflects the recycling of Molasse units. We consider that erosion of the Molasse Basin occurred in response to a shift in the drainage direction rather than because of a change in paleoclimate. Climate left an imprint on the Alpine landscape, but presumably not before the beginning of glaciation at the Pliocene–Pleistocene boundary. Similar to the northern Alpine foreland, we do not see a strong climatic fingerprint on the pattern or rates of exhumation of the External Massifs. In particular, the initiation and acceleration of imbrication and antiformal stacking of the foreland crust can be considered solely as a response to the convergence of Adria and Europe, irrespective of erosion rates. However, the recycling of the Molasse deposits since 5 Ma and the associated reduction of the loads in the foreland could have activated basement thrusts beneath the Molasse Basin in order to restore a critical wedge. In conclusion, we see the need for a more careful consideration of both tectonic and climatic forcing on the development of the Alps and the adjacent Molasse Basin.

Terminal Infill of Eocene Lake Gosiute, Wyoming, U.S.A.

Abstract Deposition of lacustrine sediments in the greater Green River Basin was progressively terminated in the middle Eocene as volcaniclastic detritus prograded across the basin; the lacustrine sediment of the Laney Member was replaced by deposition of the deltaic and fluvial sediments of the volcaniclastic Bridger and Washakie formations and the Sand Butte Bed of the Laney Member. The transition from the deposition of lacustrine to alluvial sediment also records a reversal in the direction of drainage across the basin that occurred between 49.5 Ma and 48.9 Ma. Prior to this transition, drainage entered the basin from the east and the arkosic detritus of the Cathedral Bluffs Member of the Wasatch Formation was deposited in the Washakie and Great Divide subbasins. At the same time evaporitic sediments of the Wilkins Peak Member of the Green River Formation accumulated simultaneously in the Bridger Basin, indicating that the clastic sediment was baffled east of the Rock Springs Arch, an intrabasinal structural high. The subsequent transition to deposition of the Laney Member is traditionally interpreted as an isochronous expansion of Lake Gosiute across the greater Green River Basin. Alternatively, the transition may have been diachronous with continued accumulation of the Wilkins Peak Member in the Bridger Basin coinciding with the earliest deposition of the Laney Member in the Washakie Basin. By 48.9 Ma the dominant drainage was clearly from the west, which reflects the capture of an external drainage network through the northwest corner of the basin that delivered extrabasinal volcaniclastic detritus to the greater Green River Basin. More broadly, these results illustrate that the geomorphic evolution of the landscape influenced the character of sedimentary fill in the nonmarine greater Green River Basin.

Remote sensing and GIS application for river runoff and water quality modeling in a hilly forested watershed of Japan

The main objective of this study is to present a simplified distributed modeling framework based on the storage balance concept of a Tank Model and by utilizing inputs from remote sensing data and GIS analysis. The modeling process is simplified by (1) minimizing the number of parameters with unknown values and 2) retaining important characteristics (such as land cover, topography, geology) of the study area in order to account for spatial variability. Remote sensing is used as a main source of distributed data and the GIS environment is used to integrate spatial information into the model. Remote sensing is utilized mainly to derive land cover, leaf area index (Lai) and transpiration coefficient (Tc). Topographic variables such as slope, drainage direction and soil topographic index (Tindex) are derived from a digital elevation model (DEM) using GIS. The model is used to estimate evapotranspiration (Et) loss, river flow rate and selected water quality parameters (CODMn and TP). Model verification adopted a comparison of estimated results with observed data collected at different temporal scales (storm events, daily, alternate days and every 10 days). A simplified distributed modeling framework coupled with remote sensing and GIS is expected to be an alternative to complex distributed modeling processes, which required values of parameters usually unavailable at a grid scale.

Three-dimensional reconstruction based on computed tomography images of the frontal sinus drainage pathway

This study aimed to investigate the utility of three-dimensional reconstructions of paranasal sinus computed tomography data in depicting the anatomy of the frontal sinus drainage pathway. Twenty-nine patients underwent imaging of the sinuses for various clinical indications. Variations in frontal sinus recess anatomy were determined from 0.75-mm thick coronal, axial and sagittal computed tomography images. Three-dimensional, reformatted images were generated from manually segmented volumes of interest. Observations were made on the variation and usefulness of these reconstructions. Three-dimensional, reformatted images of segmented volumes aided delineation of the spatial relationships of the frontal sinus, frontal sinus drainage pathway, infundibular and meatal direction of drainage, agger nasi cells, ethmoid bulla cells, supraorbital cells, and suprabullar cells. Three-dimensional, reformatted images of frontonasal anatomy enable improved understanding of the frontal sinus drainage pathway anatomy and of the spatial relationships between ethmoid air cells in this region. Such images may provide a useful adjunct to surgical planning and education.

The Venous Anatomy of the Anterior Abdominal Wall: An Anatomical and Clinical Study

Despite improving outcomes, venous problems in the harvest of deep inferior epigastric artery perforator (DIEP) flaps remain the more common vascular complications. However, it is apparent that the venous anatomy of the anterior abdominal wall has not been described to the same extent as the arterial anatomy. Previous anatomical studies have focused on cadaveric anatomy or excisional specimens. The current study uses in vivo computed tomographic angiography to evaluate this anatomy, in combination with a cadaveric radiographic study. Both cadaveric and in vivo studies were undertaken using eight whole fresh cadaveric specimens (16 sides) and 100 patients undergoing DIEP flap breast reconstruction (200 sides). The cadaveric component used direct catheter venography and the in vivo studies were undertaken using preoperative computed tomographic angiography, mapping in vivo venous flow. : The location, caliber, course, and distribution of the superficial and deep inferior epigastric veins were recorded. The dominance of each system and their direction of drainage were described. Mechanisms for poor venous drainage were postulated, including perforator size, midline crossover of the superficial inferior epigastric vein, and the superficial and deep inferior epigastric vein communications. The incidence of each of these anatomical factors was evaluated. The cause of venous compromise is multifactorial, with the current study showing that preoperative computed tomographic angiography may predict venous problems during flap harvest, by demonstrating perforator diameter, midline crossover, and deep-superficial venous communications.