Analysis of channel transmission losses in a dryland river reach in north‐eastern Brazil using streamflow series, groundwater level series and multi‐temporal satellite data

Abstract

Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi-temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semi-arid north-eastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events whose input river flows were smaller than a threshold did not reach the outlet of the MJR. TL events whose input flows were higher than this threshold reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre-events, and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events, and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach. † Third event in the rainy season of 2002: the second one has not been registered. { Second event in the rainy season of 2007: the first one has not been registered. *Event produced by release of water from upstream surface reservoirs during the dry season. **Not applicable. Note: The season of the event was classified as (i) beginning of the rainy season (BR), (ii) middle of the rainy season (MR), (iii) end of the rainy season (ER) and (iv) dry season (DS). We also included the order of magnitude of the groundwater extraction (GE), which occurs predominantly during the dry season. 1052A. C. COSTA ET AL.

A channel transmission losses model for different dryland rivers

“…3) belonging to an alluvium with a 20 m average depth and composed of layers of fine and coarse sand, gravel and clay (IBGE, 2003). According to Costa et al (2012), on the one hand, during the dry and at the beginning of the rainy seasons, no pre-event river flow is expected and streamflow events will create predominantly vertical infiltration into the alluvium. On the other hand, at the middle and end of the rainy seasons, river flow sustained by base flow occurs before and after streamflow events and lateral infiltration into the alluvium plays a major role during events.…”

“…On the other hand, at the middle and end of the rainy seasons, river flow sustained by base flow occurs before and after streamflow events and lateral infiltration into the alluvium plays a major role during events. Moreover, most channel transmission losses are certainly infiltrated only through the cross section of the main channel and not through the floodplains (Costa et al, 2012).…”

“…We assumed that the inflow from the drainage area between the stream gauges can be neglected for medium and large floods in the Jaguaribe River reach, because (a) the drainage area between the gauges is about 20 times less than the upstream catchment area and (b) it has about 130 surface reservoirs in its drainage network (based on Costa et al, 2012), which retains almost all of generated runoff.…”

“…However, since at the middle of the rainy seasons river flow is expected to be sustained by base flow, we may assume the riverine groundwater level to be close to the river bed at the middle of the rainy seasons, for which we applied the model. We assumed from Costa et al (2012) that the actual inflow into the simulated reach is a sum of the actual streamflow measured at the N2 stream gauge, close to the confluence of the Cariús river into the Jaguaribe River, and the one-day-before streamflow measured at the N1 stream gauge in the Jaguaribe River (see Fig. 3).…”

“…1). We used remote sensing-based data available from Costa et al (2012) to delineate the channel length and the maximum channel width, whereas field observation provided the maximum channel depth. Then, we derived stream cross-sectional areas by assuming a triangular channel cross-sectional area.…”