Finisterra, LXI(131), 2026, e42870

ISSN: 0430-5027

doi: 10.18055/Finis42870

Artigo de Investigação

FLUVIAL TYPOLOGIES IN THE BRAZILIAN DRYLANDS:

A STUDY ON THE APPLICATION OF THE METHODOLOGICAL PROPOSAL OF RIVER

STYLES

1

JOANA D’ARC MATIAS DE ALMEIDA

1

ANTONIO CARLOS DE BARROS CORRÊA

2

CARLA SUELANIA DA SILVA

WEMERSON FLÁVIO DA SILVA

1

ABSTRACT – In light of the increasing demand for methodological frameworks that underpin the conservation of

landscape diversity, particularly within physiographic contexts that have been historically undervalued, such as tropical

drylands, the River Styles methodology emerges as a significant approach. This methodology aims to generate a comprehensive

set of spatialized information that addresses the systemic interplay of regional and local controls in shaping processual and

morphological responses across drainage systems. Furthermore, it facilitates a deeper understanding of the functionality,

maintenance, preservation, and sustainable management of fluvial environments. This study applies the River Styles

methodology to a semi-arid basin in Northeastern Brazil, where the relationships between channel patterns and the formation

of aggradation landforms is still poorly explored by the geomorphological literature. Seven distinct fluvial typologies were

identified, grounded in the predominant physiographical, environmental, and processual characteristics of the area. The river

styles delineated herein can serve as a valuable reference for the assessment and classification of other basins within the

Brazilian semi-arid domain, as well as for comparative analysis with other semi-arid tropical regions situated in similar passive

continental margin contexts.

Keywords: River compartmentation; river styles; drylands; landscape units; hydrographic basin.

RESUMO – TIPOLOGIAS FLUVIAIS NAS TERRAS SECAS BRASILEIRAS: UM ESTUDO SOBRE A

APLICAÇÃO DA PROPOSTA METODOLÓGICA DE ESTILOS FLUVIAIS. Considerando a crescente demanda por

propostas metodológicas que forneçam bases para a conservação da diversidade paisagística, sobretudo em contextos

fisiográficos subestimados para esses fins como as terras secas tropicais, destaca-se a dos Estilos Fluviais, voltada à produção

de um conjunto de informações espacializadas de caráter sistêmico acerca dos controles regionais e locais responsáveis por

produzir características morfológicas e processuais ao longo das drenagens. Ademais, a metodologia aporta informações

fundamentais para o reconhecimento da funcionalidade, manutenção, preservação e gestão sustentável dos ambientes fluviais.

O presente trabalho aplicou a proposta metodológica de Estilos Fluviais a uma bacia semiárida do Nordeste do Brasil, onde as

relações entre os padrões de canal e a criação de formas de agradação são ainda pouco enfocadas pela literatura geomorfológica.

Foram identificadas sete tipologias fluviais com base nas características físicas, ambientais e processuais predominantes. Os

estilos fluviais estabelecidos para a área podem servir de referência para o levantamento e classificação de outras bacias no

domínio semiárido brasileiro, bem como para comparação com outras áreas tropicais semiáridas em contextos plataformais e

de margem continental passiva.

Palavras-chave: Compartimentação fluvial; estilos fluviais; terras secas; unidades de paisagem; bacia hidrográfica.

HIGHLIGHTS

●

The compatibility of application of river styles to Brazilian drylands.

To understand river typologies for environmental conservation and water resources in a semi-

arid context.

●

River Styles in Brazilian drylands are constantly associated with structural and landscape

controls.

Recebido: 13/04/2025. Aceite: 10/01/2026. Publicado: 11/05/2026.

Joana D'arc Matias de Almeida: joana.matias@ufpe.br

¹Federal University of Pernambuco, Cidade Universitária, 50670-901, Recife, Brasil.

²Federal University of Amapá, Oiapoque, 68980-000, Brasil.

Published under the terms and conditions of an Attribution-NonCommercial-NoDerivatives 4.0 International license.

Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

1.

INTRODUCTION

Irregular and concentrated precipitation, year-round high temperatures, and high evapotranspiration

rates characterize the drylands of the Brazilian Northeast. The irregularity of rainfall produces long periods

of drought interspersed with occasional peaks of significant rainfall, resulting in a particular

geomorphological dynamic associated with the semi-arid river environment (Almeida, 2021; Bracken &

Wainright, 2008; Souza et al., 2016). In addition to the surface processes peculiar to this type of environment,

in its tropical variety, there are impacts on land use since European colonization, with more than 400 years

of pastoral activities and traditional dry farming. These transformations have been producing complex

responses in the landscape, especially regarding the fluvial morphological units, altering channel character

and stability, and creating particular sets of morphologies (Almeida, 2021; Lima et al., 2021; Souza et al.,

2016).

Considering the diversity of river environments, proposals aimed at understanding these

geomorphological systems in their varied spatial arrangements are necessary to obtain effective responses to

water resource planning and management programs. In this sense, studies focused on the classification of

river morphology have been widely disseminated in geomorphology. Many authors have suggested

geomorphological schemes for classifying rivers, whether considering their landscape, morphological, or

hydrosedimentological aspects, such as those of Miall (1996), Nanson and Croke (1992), Whiting and

Bradley (1993) and Woolfe and Balzary (1996). Nonetheless, most studies dealing with river style

classification have bypassed the drainage systems of the semi-arid Northeast of Brazil, remaining among the

least known regions regarding their fluvial characteristics among the drylands of the world.

In recent decades, innovative methodologies have emerged to develop river typologies that are

grounded in realistic ecological and geomorphological settings. These approaches prioritize areal

requalification and the comprehensive management of river environments.

Within this framework, the River Styles theoretical-methodological model offers a nuanced

geomorphological framework aimed at elucidating the behavior and evolution of rivers on a localized scale.

This model places particular emphasis on channel dynamics and the structural characteristics of valley

bottoms (Brierley et al., 2002; Fryirs & Brierley, 2009; Souza, 2014). Its primary objective is to

systematically classify river segments by characterizing them based on a standardized set of

geomorphological and hydrodynamic attributes. This classification allows for a clear differentiation of the

behaviors and characteristics inherent to various river types (Brierley & Fryirs, 2005; Lima & Marçal, 2013).

The River Styles proposal allows us to identify the relationships between processes and forms along

rivers, in their different segments, based on the perspective that these occupy a place within the landscape

context of the watershed, in such a way that a river can present different styles, according to the particular

interaction of each segment with the landscape in its surroundings (Brierley & Fryirs, 2005).

In this way, the methodology offers a comprehensive overview of the river landscape's structure,

which can record the character and behavior of a river and offer a geomorphic assessment of its spatial and

evolutionary patterns. The proposed analysis focuses on the drainage basin, considered as a set of attributes,

which includes the morphostructural compartmentalization of the relief, the characteristics of the valley, the

plan shape and geometry of the channel, the geomorphic units of the basin and the texture of the river bed

(Brierley & Fryirs, 2005; Corrêa et al., 2009; Lima & Marçal, 2013).

In the drylands of Northeastern Brazil, the methodology was applied by Almeida et al. (2016), Corrêa

et al. (2009), Franco et al. (2022), Lima et al. (2021), Rodrigues and Souza (2020b), Rodrigues et al. (2023),

Santos et al. (2023), Souza et al. (2016). The authors focused on a morphoclimatic context, whose fluvial

landscapes have been largely overlooked. They pioneered addressing the existence of ephemeral basins

characterized by sui generis aggradational forms in this Brazilian region, differentiated from intermittent

rivers.

The concept of River Styles offers a versatile framework for understanding the dynamics of rivers and

landscapes, yet its application in semi-arid basins remains underexplored. This is notable given the potential

benefits that its outcomes could yield for territorial planning. In this context, the present study seeks to apply

the River Styles methodology within a semi-arid basin in the Brazilian Northeast.

The primary objective is to establish a new typological framework for the identification of

aggradational units. This framework aims to provide a more robust characterization that could serve as a

foundation for the conservation and rehabilitation of ephemeral river channels. Such an approach is crucial,

considering the diverse uses and environmental services these river systems offer to the region.

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

2.

METHODOLOGY

The application of the River Styles methodology requires the creation of a database composed of a list

of integrated geospatial attributes concerning the river forms, processes, and connections established between

channels. This spatialized information on the morphological and structural aspects of the channels and their

segments constitutes the basis for the four-tiered River Styles analysis and provides a basis for predictions

on river behavior (Brierley & Fryirs, 2005).

The first stage of the method involves the identification, interpretation, and mapping of river styles in

a river basin. These procedures are the basis for characterizing the river behavior. The second stage consists

of conducting assessments of river character and behavior from a dynamic perspective, where forms and

processes are evaluated from an evolutionary standpoint. The third stage corresponds to evaluating the future

trajectory of changes and the recovery potential of the river channel. Finally, the fourth stage focuses on river

management applications by constructing qualitative and prognostic scenarios (Almeida, 2017; Brierley &

Fryirs, 2005).

In this work, the methodology proposed by Brierley and Fryirs (2005) was adapted, based on its first

two stages, to provide a detailed geomorphological model to understand the behavior and evolution of the

river system up to its current spatial arrangement. This work adapted the River Styles methodology with

emphasis on the interaction between structural and anthropogenic conditions, in order to complete the

definitions for the semi-arid region proposed by Lima et al. (2021), Souza (2014) and Souza et al. (2016).

The identification of River Styles is based on the analysis of river sections, for which the degree of

valley confinement, the number of channels, and the condition of channels' lateral stability are defined. The

confinement classification aims to establish whether or not the flow overflows beyond the limits of the

channel, and it is possible to identify three classes. The confined valley corresponds to the sectors that present

floodplains in less than 10% of the river section; the partially confined valley occurs when 10 to 90% of the

analyzed segment presents a discontinuous alluvial plain; while in the unconfined pattern, more than 90% of

the section presents a continuous floodplain (Brierley & Fryirs, 2005; Souza, 2014).

In this stage, orthophotomaps from the Pernambuco 3D Project, at a scale of 1:5 000, were used to

identify current drainage patterns and fluvial deposits. As a result, the approach sought to build an

information framework presenting the river's characteristics, behavior, and controls. At this stage,

representative channel sections were identified. Next, the adjustment capacity of each section was analyzed.

To assess the processual state of a river in relation to its surrounding landscape, it is essential to

determine the adjustment capacity of each river segment and establish its specific morphology. The

evolutionary trajectory of each segment must be analyzed to identify any irreversible changes and to pinpoint

reference sections that facilitate a more in-depth interpretation of the prevailing geomorphological conditions

(Almeida, 2017; Brierley & Fryirs, 2005). Fieldwork was conducted to substantiate the typologies identified,

following a comprehensive geomorphological mapping of representative areas.

To construct the river typologies, it was necessary to compartmentalize the landscape units that make

up the watershed. To this end, primary data, such as the Digital Terrain Model (MDT) from the Pernambuco

3D Project (Pernambuco, 2013), were used on a scale of 1:5 000 with an altimetric precision of 25cm. These

data served as a basis for updating the landscape compartmentalization map proposed in Almeida (2021) for

the basin and generating topographic profiles.

Secondary data from other cartographic bases were also used, including geology (Serviço Geológico

do Brasil [SGB], 2005a, 2005b, 2005c), geomorphology (Almeida, 2017), and pedology (Oliveira, 2016).

Land cover and land use data were obtained from Almeida et al. (2016), which generated a mapping based

on the legend proposed by Food and Agriculture Organization of the United Nations [FAO], (2014).

2.1. Study area

The Riacho Grande Basin (fig. 1), with an area of 316km², is located in the center of the state of

Pernambuco, encompassing parts of the municipalities of Serra Talhada, Calumbi, and Flores, delimited by

the geographic coordinates of 7°55' S / 37°55' W and 8°08' S / 38°12' W (Almeida, 2017; Almeida et al.,

2016). The watershed constitutes a sub-basin of the Pajeú River, a tributary of the São Francisco River, the

largest exotic river in South America, and the only perennial course to cross the semi-arid Northeast of Brazil.

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

Fig. 1 – Location and hypsometry of the Riacho Grande basin.

Fig. 1 – Localização e hipsometria da bacia do Riacho Grande.

Source: Almeida (2021) and Almeida et al. (2025)

Regarding the climatic context, the Riacho Grande basin is located in the semi-arid tropical domain of

the interior of the Brazilian Northeast, with average monthly temperatures ranging from 22 to 26°C, total

annual precipitation of less than 800mm, and an irregular interannual regime controlled by global-scale

phenomena. The area is prone to prolonged droughts or torrential rains concentrated over short periods, even

in unlikely times, which favors the occurrence of floods and inundations (Almeida et al., 2012; Alves et al.,

2017; Aragão, 1998; Barros, 2018; Freire et al., 2011).

Identifying landscape physiographic elements allowed the definition of the spatial controls operating

over the fluvial domain. Relief morphostructural units were identified by analyzing the different classes of

terrain roughness, which led to the basin's subdivision into three larger sectors (table 1 and fig. 2): the Pajeú

Interplanaltic Depression, Structural Ridge Massifs, and the Betânia Sedimentary Plateau.

Table I – Summary of the lithological framework of the study area.

Quadro I – Síntese dos dados litológicos da área de estudo.

Morphostructural Unit

Lithological Framework

Landscape setting

São Caetano Complex Afogados da Ingazeira Complex

Floresta Complex Indiscriminated granitoids Recanto - Riacho do Forno

Suite

Vegetated or unvegetated dissected

pediments

Pajeú intermontane

depression

Alluvial deposits

Alluvial plains

Structural ridge massifs

Prata Intrusive Suite Terra Nova Intrusive Itaporanga Intrusive Suite

NE-SW / E-W trending elongated ridges

Homoclinal sedimentary plateau

Betânia sedimentary plateau

Tacaratu Formation

Source: Serviço Geológico do Brasil (2014)

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

The Pajeú Intermontane Depression corresponds to a strip of NE-SW elongated lowlands, confined

between the Remobilized Massifs of the Transversal Zone Domain and the Western Escarpment of the

Borborema Highlands (Corrêa et al., 2010). The Riacho Grande basin is installed on this low-lying flat

compartment, structured in metamorphic complexes and Neoproterozoic granite plutons, mostly covered by

the xerophytic thorn-scrub vegetation of the caatinga. The lowlands are transversed by mylonitic ridges

subordinated to the structural controls of the NE-SW and E-W trending Neoproterozoic Shear Zones, where

some sections of the larger channels are superimposed (Almeida et al., 1967; Sial, 1984; Silva Filho et al.,

1987; Silva Filho e Guimarães, 1990).

Fig. 2 – Geology of the Riacho Grande basin and its surroundings.

Fig. 2 – Geologia da bacia do Riacho Grande e arredores.

Source: Serviço Geológico do Brasil (2014)

The climatic and geological characteristics of the region significantly influence soil development, as

highlighted by Corrêa et al. (2014). In the semi-arid Northeast of Brazil, the soils demonstrate a denudational

balance that tends to prioritize erosion over pedogenesis. This process results in a distribution of soil classes

that is primarily governed by lithological controls, geomorphic compartmentalization, and land use types.

Within this framework, the Fluvisols present in the Riacho Grande basin are noteworthy; these soils are

formed from recent alluvial deposits found in river plains and their associated terraces.

Additionally, the presence of Leptosols, which are shallow soils containing gravel, and Arenosols,

characterized by sandy textures that are highly susceptible to erosion, is significant. The Arenosols exhibit a

high infiltration capacity and notably low clay content.

Planosols are another class of greater recurrence in the Riacho Grande basin. They exhibit light-

colored horizons and abrupt changes in texture, are shallow, have low permeability, and are more susceptible

to erosion processes (Almeida, 2015; FAO, 2014; Oliveira, 2016), especially when related to the intensity of

human activities in the sectors close to the terraces and riverbeds.

In these regions, Fluvisols and Planosols are the dominant types found at the interface between the

alluvial plains and the adjacent rocky pediments, which delineate the lateral boundaries of the alluvial

domain. Within this geoenvironmental unit, a range of agricultural practices is undertaken, including cattle

ranching and dryland farming, particularly by smallholder farmers.

The pediments cover a large part of the Riacho Grande basin, alternating areas with preserved

vegetation cover and areas under agricultural activities closer to the main channel. These are overall level

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

surfaces with a ramp morphology, occurring between 450 and 550 meters (Almeida et al., 2016). These

compartments are primarily structured in the sequences of metamorphosed metasedimentary rocks of the São

Caetano Complex (SGB, 2001) to the north of the Afogados da Ingazeira Shear Zone and in the orthogneisses

of the Floresta Complex. Leptosols and Luvisols predominate on the pediment ramps, while Planosols occur

in the fluvial plains.

The agricultural activities carried out in the areas of contact between the pediment and the alluvial

plains are those aimed at subsistence, carried out on small family properties, which take advantage of areas

capable of holding soil moisture even after the short rainy season to grow short-cycle crops.

The semi-arid nature of the region significantly influences agricultural development, necessitating the

construction of small-scale dams and the drilling of shallow wells. The prevalence of these rudimentary dams

is closely associated with the Fissural Hydrogeological Domain, characterized by crystalline rock formations.

In this domain, water storage is primarily dictated by secondary porosity, which is manifested through

fractures and fissures. This results in underground reservoirs that are often spatially limited, discontinuous,

and unpredictably distributed. Consequently, the wells in this region typically exhibit low flow rates.

Furthermore, due to inadequate water circulation, elevated rates of evapotranspiration, and the specific

characteristics of the bedrock, the water is frequently prone to salinization (Ministério de Minas e Energia

[MME], 2009).

The Betânia homoclinal sedimentary plateau is characterized by a continuous cover of caatinga

vegetation, which marks its distinctive landscape unit within the basin. This region is notable for its

asymmetric ridges, featuring slopes exceeding 15°, and is further defined by dip-slip slopes that are dissected

by canyons and steep valleys. The morphological characteristics observed in the area are largely attributed

to the adaptation of the drainage network to the predominant psammite-psephitic lithotypes, which exhibit

significant diagenesis and sub-vertical fracturing.

In this landscape unit (fig. 3), aggradational areas are characterized by alluvial plains presenting

sediments of sandy, clayey, and gravelly textures. In contrast, sandy eluvial-colluvial sediments occur at the

foot of the elevations. Prevailing soil classes in this landscape unit are Leptosols, rocky outcrops on the higher

hillslopes, and Arenosols at the foot of the slopes. Associations with Acrisols were also observed to a lesser

extent.

Fig. 3 – Landscape units of Riacho Grande basin

Fig. 3 – Unidades de Paisagem da bacia do Riacho Grande.

Source: Almeida et al. (2025)

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

3.

FLUVIAL COMPARTIMENTS AND TYPOLOGIES

To comprehend the fluvial dynamics within a semi-arid environment, a detailed analysis of the

channels in the Riacho Grande basin was conducted, employing the River Styles framework established by

Brierley and Fryirs (2005). The analysis commenced with an exploration of fluvial compartmentalization, a

concept that reflects the regional influences on channel morphology and highlights the prevailing surface

processes within the landscape framework.

This approach categorizes the channels based on the degree of valley confinement, further subdividing

them according to shared characteristics regarding the distribution of floodplain deposits along their lengths.

Specifically, confined valleys are identified as those that either lack floodplains entirely or exhibit them

sporadically, characterized by unilateral overflow. In contrast, partially confined valleys display

discontinuous floodplains throughout the majority of their stretches. Finally, laterally unconfined valleys are

distinguished by the presence of bilateral overflow deposits and the continuous development of alluvial

plains.

A longitudinal profile of the main channel has been constructed (fig. 4), delineating the various river

compartments within the Riacho Grande Basin. In the section of the profile up to an elevation of 530 meters,

a predominantly erosive behavior is observed, which is characteristic of confined valley systems.

Conversely, downstream of this elevation, the profile becomes increasingly smoother, indicating a

transition to depositional processes. This shift is reflected in the landscape through laterally unconfined

valleys, which are influenced by features that disrupt sediment transfer within the channel. These disruptions

may be attributed to both geological structures and anthropogenic interventions, leading to the formation of

zones of sediment storage.

Between 500 and 450 meters, the river dynamics combine erosive and depositional processes. In this

section, the channel is partially confined and is characterized as a sediment transfer zone. In this segment,

the knickpoints record the existence of structural controls on the geometry of the channel, characterized by a

sequence of rocky sills along the riverbed. Then, the profile becomes smoother again, evidencing a

resumption of depositional processes close to its mouth.

Fig. 4 – Longitudinal profile of the Riacho Grande (A). Main channel of the Riacho Grande and its compartmentalization (B).

Fig. 4 – Perfil longitudinal do Riacho Grande (A). Canal principal do Riacho Grande e a sua compartimentação (B).

Source: Authors

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In order to elucidate aspects of the drainage dynamics and behavior, the channels were subdivided into

segments, defining typologies that translate the landscape context in which they are inserted on a local scale.

Thus, considering the landscape units, the river compartmentalization, and the local geomorphological

characteristics, seven channel typologies were defined in the Riacho Grande Basin (fig. 5): rocky confined

channels; rocky confined channels with discontinuous floodplains; sandy confined channels with

discontinuous floodplains; low sinuosity channels with discontinuous floodplains; channeled valley with

filling; filled valleys; and filled valleys in homoclinal morphostructure.

Fig. 5 – Fluvial typologies in the Riacho Grande basin.

Fig. 5 – Tipologias fluviais na bacia do Riacho Grande.

Source: Opentopography, Copernicus (2025)

3.1. Confined pattern

The confined valleys within the Riacho Grande Basin are generally devoid of floodplains, or, when

present, these features are limited in both spatial extent and frequency. Lithological and structural controls,

including fractures and mylonitic foliation, significantly influence the morphological characteristics of these

valleys. The topography leads to the formation of single, continuous, low-order channels predominantly

shaped by erosional processes. These channels exhibit low sinuosity and medium to high slopes in

longitudinal and lateral profiles. Based on their distinct characteristics and behavior, these channels can be

classified into three primary typologies: rocky confined channels, rocky confined channels with

discontinuous floodplains, and sandy confined channels with discontinuous floodplains.

With low incidence in the Riacho Grande basin, channels of this type have stable banks and steep

slopes, with direct contact between the bed and the rocky substrate (fig. 6). Erosion and transport predominate

in their evolution. They are located over sediment source and transfer areas, with punctual deposition

characterized by the development of small pockets of sediment retained upstream of rocky sills or at the

confluence of tributaries. These deposits are subject to reworking and evacuation during high-magnitude

rainfall events. The distribution of artificial dams also contributes to the genesis of these depositional features

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During extended drought periods, river channels exhibit a lack of flow, which unveils the presence of

gradient disruptions and a sequence of rifles and pools. Upon the resumption of flow, the ensuing torrents

exhibit both high capacity and competence, serving as a source area for the downstream segments. This

particular typology is characterized by minimal anthropogenic influence along its course, featuring dense

shrubby caatinga vegetation. In this context, human interventions are typically localized, manifesting as the

construction of rustic dams and the intersection of channels by unpaved roads.

Fig. 6 – (A) Segment of a rocky confined channel, (B) land use, (C) lateral and longitudinal profiles highlighted (point 1), (D)

the upper detail on the right refers to sediments trapped near the confluence, where (A) represents the flow direction and (A)

the confluence.

Fig. 6 – Segmento de canal confinado rochoso, (B) uso da terra, (C) destaque para perfis longitudinal e lateral (ponto 1),

(D) o detalhe superior à direita refere-se aos sedimentos aprisionados perto da confluência, onde (A) representa a direção

do fluxo e (B) a confluência.

Source: Authors. Photography: Joana Almeida, 2019.

In the Riacho Grande basin, rocky confined channels with discontinuous floodplains are prominent

features characterized by single, continuous channels that exhibit rocky beds, with floodplains typically

confined to one side. These channels are situated in transitional zones where there is a gradient in sediment

transfer capacity, ranging from high to low.

The channels are typically entrenched and possess asymmetric margins, which display varying degrees

of resistance that influence their lateral adjustment. This category of confined channels is widespread

throughout the Riacho Grande basin, distinguished by an average sinuosity in regions that are predominantly

subject to erosion and sediment transport. In certain wider segments, occasional floodplains develop in

response to episodic flash floods (fig. 7).

Among the geomorphic units in this typology, lateral bars, floodplains, and riffle-and-pool sequences

predominate. Depositional processes occur through flooding on gentle convex banks, while concave and

steep banks remain controlled by lithology. In planform, these channels become wider downstream,

evidencing a transitional behavior towards a predominance of depositional features. These, in turn, occur as

temporary accumulation zones, composed mainly of gravelly- sandy sediments, reworked during high-flow

episodes.

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In the Riacho Grande basin, this typology is mainly associated with the dissected pediments landscape

compartment. In addition to structural controls, human interventions influence river behavior in this sector.

Small rural settlements are located directly around the channels, with short- cycle crops and animal husbandry

on slopes with eluvial cover. Due to the traditional agricultural activities, the presence and construction of

dams and rustic reservoirs temporarily interrupt the longitudinal connection along the channels. The same

occurs with the interposition of unpaved rural roads and the Transnordestina railway works, which remobilize

sediments from the hillsides to the channels. During the long dry season, sediments remain trapped until the

arrival of the first torrential episodes in late summer.

Fig. 7 – (A) Rocky confined channel with discontinuous floodplain, (B) land use, (C) longitudinal and lateral profiles

highlighted (Point 2). (D) The image in the upper right corner refers to the deposition of a pocket plain in a bedrock channel,

where (A) represents rupture and (B) pocket-plain sediment deposition, while the red arrow indicates flow direction.

Fig. 7 – (A) Canal rochoso confinado com planície de inundação descontínua, (B) uso da terra, (C) perfis longitudinais e

laterais destacados (Ponto 2). (D) A imagem no canto superior direito refere-se à deposição de uma planície de inundação

em um canal rochoso, onde (A) representa a ruptura e (B) a deposição de sedimentos na planície de inundação, enquanto a

seta vermelha indica a direção do fluxo.

Source: Authors. Photography: Joana Almeida, 2014

The sandy confined channels with discontinuous floodplains represent the most prevalent subtype

within the confined channels category (fig. 8). These channels are characterized by single, continuous

channels, with a substrate formed by alluvial deposits that overlay the dissected surface of rocky pediments.

Rocky outcrops are frequently found within the channel, contributing to the banks' structural resistance.

These outcrops are linked to more resistant lithologies that influence the flow dynamics.

As a result, sediment deposition occurs upstream of these rocky formations, forming pocket plains

embedded within alveoli, which are separated by segments of straight, confined channels. The banks exhibit

asymmetry, characterized by the accumulation of lateral bars, shallow floodplains on one side, and steep,

more resistant rocky banks on the other.

The segments under analysis stand out due to the predominance of bed incision and thalweg

entrenchment over erosion processes on the banks, as observed in the cross-section profiles. The greater

resistance of the banks limits the adjustment capacity and lateral migration of the channel, restricting the

sediment accommodation spaces to specific sectors of the river where structural controls, such as the

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

intersections of fractures of different directions, allow the widening of the valley (alveoli), as verified in

planform through the arrangement of depositional features in sections where the channel presents inflections.

Longitudinally, these segments occur adjacent to partially confined channels, contributing as source

and transfer areas for sediments during high-magnitude torrential events. Regarding land use and land cover,

the sectors of the Riacho Grande basin under this typology present low levels of human intervention, except

for rustic dams and unpaved roads.

Fig. 8 – (A) Sandy confined channel with discontinuous floodplain, (B) land use, (C) highlighting longitudinal and lateral

profiles (Point 3). In the below right corner, an entrenched channel in sandy bed, where (D) represents channel incision in

2014 and channel filling in 2019. The red marker indicates a rocky sill.

Fig. 8 – (A) Canal confinado arenoso com planície de inundação descontínua, (B) uso da terra, (C) destacando perfis

longitudinais e laterais (Ponto 3). No canto inferior direito, um canal entrincheirado em leito arenoso, onde (D) representa a

incisão do canal em 2014 e o preenchimento do canal em 2019. O marcador vermelho indica uma soleira rochosa.

Source: Authors. Photography: Joana Almeida, 2014; 2019.

3.2. Partially confined

Partially confined valleys were identified according to their character and fluvial behavior, with low

sinuosity channels and discontinuous floodplains. They are commonly located downstream of confined

valleys and stand out as sediment transfer zones. In general, they are quite representative in the study area,

especially along the main channel of the Riacho Grande. They constitute transitional typologies characterized

by a combination of erosion and depositional processes.

In specific segments, depositional dynamics dominate (fig. 9), leading to pronounced accumulation

morphologies, such as point bars and floodplains. The valleys formed in this context tend to be broad and

contain discontinuous channels that operate under low energy conditions, displaying reduced competence.

The deposition of silty-sandy materials prevails both in the channel bed and along the banks. This

geomorphological section demonstrates a moderate to high capacity for adjustment, as lateral channel

migration occurs due to erosional processes impacting the concave banks and sediment accumulation over

the convex banks. Additionally, the influence of overflow deposition during flooding events further

contributes to accretional physiognomies.

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

Fig. 9 – (A) Low sinuosity channel with discontinuous floodplain, (B) land use, (C) the longitudinal and lateral profiles of the

section (Point 4), (D) in the upper right corner, a low sinuosity channel, where (A) represents the lateral deposition of

sediments on the convex bank, with adjacent overflow, while (B) represents a pool adjacent to the rocky sill (indicated by the

red marker) and a longitudinal bar downstream.

Fig. 9 – (A) Canal de baixa sinuosidade com planície de inundação descontínua, (B) uso da terra, (C) perfis longitudinal e

lateral da seção (Ponto 4), (D) no canto superior direito, um canal de baixa sinuosidade, onde (A) representa a deposição

lateral de sedimentos na margem convexa, com transbordamento adjacente, enquanto (B) representa uma poça adjacente à

soleira rochosa (indicada pelo marcador vermelho) e uma barra longitudinal a jusante.

Source: Authors. Photography: Joana Almeida, 2015.

The upstream sectors of the laterally unconfined channels are located on hillslopes with eluvial cover,

where agricultural activities intensify human interventions in sediment pockets and flat floodplain areas.

Agricultural practices also contribute to sediment remobilization from the banks to the channel bed. The most

representative stretch of this typology refers to the main channel of the Riacho Grande, which is especially

impacted by the construction of dams for water impoundment. Human aggradational morphologies develop

upstream of such dams.

3.3. Laterally unconfined

Laterally unconfined valleys are prevalent in the low-slope sectors of the Riacho Grande Basin,

characterized by a predominance of aggradational forms. Channels in this typology exhibit significant

capacity for both lateral and vertical adjustment, resulting in broad, shallow, and bilaterally symmetrical

floodplains.

In many instances, the landscape features discontinuous incisions of single or multiple shallow

channels; however, in most scenarios’ channels are frequently absent. This cut-and-fill channel pattern is a

defining characteristic of the alluvial river segments found in the semi-arid Northeast (Lima et al., 2021;

Mabesoone, 1981). As a result, the fluvial landscape is dominated by unchanneled depositional sectors,

particularly observed in the vicinity of confluences.

These segments have a high incidence of human interventions, mainly focused on agricultural

activities, in addition to the implementation of dams for flow containment and water storage. These dams,

typical of the drylands of the Northeast, influence the distribution of sediments along the channel, establishing

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Almeida, J. D. M., Côrrea, A. C. B., Silva, C. S., Silva, W. F. Finisterra, LXI(131), 2026, e42870

upstream, extensive floodplains. Considering these local particularities of each planform section, the laterally

unconfined valleys were subdivided into channeled-filled valleys, filled valleys, and filled valleys in

homoclinal morphostructure.

The segment depicted in figure 10 pertains to Varzinha Creek, which exhibits gentle slopes and a

longitudinal equilibrium profile. This indicates significant energy dissipation and highlights the prevalence

of depositional processes within the creek's dynamics.

Fig. 10 – (A) Channeled filled valley, (B) land use, (C) lateral and longitudinal profiles of the section (Point 6), (D) in the

upper right corner, a section of channeled filling in the Varzinha Creek, where (A) represents the Flood Plain and (B) the

Sandy Lateral Bar, while the red arrow represents the flow direction.

Fig. 10 – (A) Vale preenchido canalizado, (B) uso da terra, (C) perfis lateral e longitudinal da seção (Ponto 6), (D) no canto

superior direito, uma secção de preenchimento canalizado no Riacho Varzinha, onde (A) representa a Planície de Inundação

e (B) a Barra Lateral Arenosa, enquanto a seta vermelha representa a direção do fluxo.

Source: Authors. Photography: Joana Almeida, 2019.

As a result, the formation of point bars and adjacent marginal dikes along the alluvial plain is evident.

Point bars develop as sandy sediments accumulate on banks that flank rocky outcrops and boulders. These

formations are closely associated with litho-structural controls, which are influenced by the intersection of

NE-SW and NW-SE lineaments, as illustrated in figure 11.

These controls are manifest in the planform through abrupt inflections in the drainage pattern. Notably,

during the dry season, certain areas within this section remain inundated, while in the rainy season, the flow

reaches elevations that surpass the level of the alluvial plain, resulting in the reworking and deposition of

sediments throughout the valley

This section is approximately 8.5km long, with erosive process predominating up to an elevation of

445km. This behavior is associated with the interposition of an artificial base level resulting from a dam built

upstream of the segment. The difference in altitude between the base levels causes the erosive processes to

recur and channel dissection to resume. As the flow progress, aggradational morphologies appear in the

middle of the channel.

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Fig. 11 – Point bar adjacent to a rock outcrop. A – sandy point bar.

Fig. 11 – Barra em pontal adjacente a soleira rochosa. A – barra em pontal arenosa.

Source: Authors. Photography: Joana Almeida, 2019.

The sections classified as filled valleys (fig. 12) are wide, flat, low-sinuosity, sediment-filled, and

preserved alluvial valleys with no channeled flow. They are located at the valley bottoms with low lateral

and longitudinal slopes, reflected in the flow's low capacity and competence, with a predominance of

aggradational processes. They are configured as low-energy fluvial units, with a predominance of

depositional morphologies, especially in the middle of the channel, associated with spasmodic overflow

events, which, according to Brierley and Fryirs (2005), construct temporary morphologies within the bed

materials.

Fig. 12 – (A) Unchanneled filled valley, (B) land use, (C) longitudinal and lateral profiles of the section (Point 5). (D) In the

upper right corner is a mid-channel morphology, where (A) refers to the longitudinal bar, and the red arrow indicates the flow

direction.

Fig. 12 – (A) Vale preenchido não canalizado, (B) uso da terra, (C) os perfis longitudinal e lateral da seção (Ponto 5). (D)

No canto superior direito, há uma morfologia do meio do canal, onde (A) se refere à barra longitudinal e a seta vermelha

indica a direção do fluxo.

Source: Authors. Photography: Joana Almeida, 2019.

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In this typology, discontinuous ravines and small ponds may be frequent, which are associated with

low-flow stages, where the flow is limited to depressions or small incisions in the alluvial surface, with the

accumulation of suspended sediments. During periods of higher flow, the valley is entirely covered by a sheet

of water. At this time, sediments are remobilized and rapidly deposited as the flow energy is dissipated

downstream (fig. 13), resulting in the formation of floodouts.

Fig. 13 – Filled valley. A – Dry period (2015). B – Following the rainny season (2019).

Fig. 13 – Vale preenchido. A – Período de seca (2015). B – Após o período chuvoso (2019).

Source: Authors. Photography: Joana Almeida. A) 2015 B) 2019.

Brierley and Fryirs (2013) define floodouts as geomorphic units that are associated with depositional

sectors within flood-prone areas. These features arise from the intersection of a discontinuous channel that,

influenced by changes in base level, transports sediments downstream into a valley surface that shows little

to no incision. The resulting sedimentary deposits typically exhibit a fan-like morphology, primarily

composed of bedload materials. However, the low gradient of the channeled flow allows for the deposition

of finer materials as well, due to the dissipation of energy.

According to the authors, these sedimentary flood lobes, referred to as floodouts, distribute themselves

over a relatively flat surface characterized by slightly convex edges, predominantly filling the lower

elevations of the valley bottom.The filled valleys are located in different sectors of the Riacho Grande Basin,

usually adjacent to partially confined sections or filled valleys with dominant structural controls.

These areas function as storage basins (sinks) for sediments from the main channel and tributaries,

trapping sediments between confluences and promoting river disconnection in the channel-channel and

channel-tributary relationship. In these areas, there is an intensification of human activities, both on the banks

and in the middle of the channel, with the practice of agriculture, which intensifies erosion processes.

Installing open wells (locally known as cacimbas) is common to take advantage of the water storage in the

alluvial aquifers.

Also noteworthy in the Riacho Grande Basin are the filled valleys under the morphostructural

influence of the Betânia homoclinal plateau (Corrêa et al., 2024), located on the dip-slip slope of the residual

landforms, here named "filled valley in homoclinal structure".

These valleys have hollow-shaped headwaters, where surface flows converge, filling the adjacent

accommodation spaces with sandy sediments from the weathering of the Tacaratu Formation (Siluro-

Devonian), forming extensive alluvial plains (fig. 14). This configuration is evident in the analysis of the

longitudinal profile of the highlighted section, where the river presents erosive behavior above 700m under

a high gradient, with the gradual smoothing of the longitudinal profile below 650m, indicating the beginning

of the accumulation zone.

This typology is characterized by irregular valleys with asymmetrical cross-sectional profiles that

widen downstream. Their capacity for lateral adjustment is limited due to the lithostructural controls of the

silicified sandstones of the Tacaratu Formation. The alluvial plains differ from the other typologies by the

abundance of gravel and coarse sand, which attest to the proximity and control of the source area (fig. 15).

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