Introduction

Increasing the population and improving the level of social welfare and demand for food needs are effective factors in the destruction of ecosystems and environmental damage. Inefficient utilization of resources in watersheds causes this destruction, which has results such as the occurrence of heavy floods and environmental degradation. A large part of Iran is located in the arid region, so its rainfall is about one-third of the world. In recent decades, a large part of Iran has been exposed to severe floods, and over time, the volume of losses of life and property and environmental damage has increased (Jahantigh and Jahantigh 2020). Consequences of such circumstances are including lack of water infiltration into groundwater aquifers and reduction of water available for agriculture and reduction of income, increase the irregular migration due to lack of income, and destruction of the environment (Foster and Chilton 2003; Cotti et al. 2022; Yu et al. 2022). Therefore, optimal control and use of existing floods is a basic need of natural ecosystems. Human activities in natural ecosystems have a great impact on floods and flooding. With urban development, due to the increase in impermeable surfaces, the volume and also occurrence of floods increase (Ghafouri 1996; Li and Xu 2002; Abiye 2022). Floods are one of the most important causes of environmental degradation. This phenomenon destroys soil and transfers into the rivers and canals and causes them to be blocked. Such a situation creates a basis that subsequent floods, due to the lack of suitable drainage channels, cause the destruction of natural ecosystems and ultimately cause climate change and environmental crises (Yang et al 2003; Arnell and Gosling 2016). Runoff control is possible in different ways, as the use of each method depends on the environmental conditions and socio-economic and environmental effects on the ecosystem (Bailey and Ayres 1936; Brooks et al. 1991; Amini et al. 2013). Various factors and methods have been studied to reduce floods and prevent them worldwide, one of which is the use of small consecutive dams (Jons 2000; Wang et al. 2021).

Pawar (1998) reported that with the implementation of watershed management operations such as the construction of small dams, the survival rate of vegetation in the Maharashtra watershed in India, areas with shallow foothills and semi-deep soils, has increased to 23 and 47%, respectively. Also, the occurrence and volume of floods have been reduced, which has led to a decrease in the erosion rates in the mountains and highlands area from 42.68 to 12.79%. The results of researches on the impacts of watershed management activities on floods showed that the occurrence and volume of floods were significantly reduced by performing mechanical and biological activities (Ranade and Gupta 1996; Sarka 2022). The other study in the Megalia watershed of India demonstrated that with the implementation of watershed management, sediment production has decreased to 0.16218 hectares per square kilometer, which has improved environmental indicators including rainfall reserves and vegetation (Rymbai and Jha 2012). Moreover, some report shows that rangeland management based on watershed management activities in US watersheds has led to increase vegetation and soil moisture storage and also reduce runoff and sediment volume (Wine et al 2012). Delayed structures, in addition to preventing runoff junction at upstream, by storing flood flows in their reservoir and reducing the flow velocity of runoff, cause a lag time to reach runoff to its maximum outflow in the basin. Moreover, these structures can reduce the maximum flood discharge with a return period of 1000 years to the equivalent discharge with the occurrence of floods with a return period of 25 years, after control and penetration into soil. Reference studies showed that small structures play an important role in increasing infiltration and reducing sediment and runoff in mountainous areas. About 87 million hectares of Iran are mountainous areas where there is a field of watershed management operation. To succeed in the implementation of watershed management programs, various factors such as the importance of the environment, sustainable development, improving crop and livestock production, and socio-economic development by improving the living conditions of stakeholders in watersheds are considered. Therefore, in this study, the performance of watershed management measures and their environmental impact in the Taftan watershed were studied.

Materials and methods

Study area

The study area is about 30 km northwest of Khash city (in the Taftan watershed) with an area of 1100 ha (with coordinates of 60˚ 46′ 11″–60˚ 57′ 17″ east longitude and 28˚ 31′ 40″–28˚ 40′ 40″ north latitude) that is located at an average altitude of 2301 m above sea level (Fig. 1). The watershed has a dry climate with critical ecological conditions. The average annual temperature of the watershed is 15.7 °C, and the warmest and coldest months of the year are August (36.2) and February (1–1.1), respectively. The average annual precipitation of this region is 174.9 mm, most of which occurs in winter. This area has a high evaporation rate and low humidity. The plant community of the study area includes 264 species and belonged to 47 families, and vegetation condition ranges from poor to good. There are three types of plants in this watershed. Annual and perennial plants account for 62.4% and 37.6% of the flora list, respectively. Investigation of vegetative form of plant species also shows that the highest frequency is related to herbaceous plants, and the lowest is related to quasi-grasses. Geologically, this watershed is located in the flash zone of eastern Iran (Jahantigh 2013, 2017).

Fig. 1
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Location map of the study area. A map of Iran, B the location of Sistan and Baluchestan Province in Iran, C the location of the Taftan watershed in Khash County, D location of the studied area in Taftan watershed, E Google Earth image for the study area includes check dams, river, and basin boundary, F digital elevation model (DEM), and G sub-basin map of the study area

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Methodology

To conduct this research, the basic field reports were studied. Field visits were made to the watershed, and the dimensions of check dams constructed were estimated. Rainfall and flood flows were measured at the required time. To measure the flood volume, graduated scales were installed at the reservoirs and the outlets of the watershed. The volume of the flood was measured for each rainfall event (Merz et al. 2006; Shope et al. 2013). The infiltration rate was estimated in the check dam reservoir using a double-ring method (Ronnqvist 2018). As well as flow duration was tested before and after watershed management operation using the direct measurement method (Pawar et al. 2023). Also, by employing satellite image, the effect of watershed management operation on the agricultural land area was investigated. To achieve this purpose, first high-resolution images related to the years before (2004) and after (2017) watershed management operations were taken from the Google Earth imagery using Elshayal Smart GIS software. Images mosaic was performed by using Global Mapper software. After that, by the visual interpretation method, agricultural land use was determined, and the area of this land use was calculated for the study period by using GIS software (Hegazy and Kaloop 2015; Malarvizhi et al. 2016). Additionally, hydrological analysis (analyzing flood discharge, surface runoff, and its correlation with runoff infiltration), soil erosion control (determine sediment transport), and land use changes (changes in agriculture area) were employed to reveal the environmental effects of watershed management operation by descriptive and inferential analysis (Jahantigh and Jahantigh 2020; Pramudiya et al. 2022). Statistical analyses were performed using (by compare mean t-test) the SPSS 18 software.

Results

Forty-five check dams in this watershed were surveyed, of which 87.5% and 12.5% of them are loose rock-cement and gabion, respectively. The aim of constructing these structures was to ecologically stabilize the relevant watershed by controlling floods and sediment and storing it to meet the water required for agriculture and the environmental sustainability of the region. Most of these structures are based on scientific construction methods, and each of them has a spillway, wing, and stilling basin. The size of these structures is different and adequate for their specific site. The smallest and largest constructed dams in this watershed are 10 and 42 m long, respectively. The base width of some check dams reaches 3.5 m. But the upper width is usually 1 m, and their maximum height reaches 6.7 m. The spillway of check dams has made in different dimensions; their height is about 1 m, and their length varies and is dependent on runoff volume. In 2010, during the autumn season, several traces of rain occurred, but from 20 to 23 February, 79.3 mm of rain occurred, which led to create effective floods and also sediment production in the study area. Moreover, in March of the mentioned year, the rain onset from the ninth day and continued until the eleventh day and the total rainfall was 18.9 mm during 3 days. Although the occurrence of this rainfall did not cause flooding, it increased the base flows of the main waterway (Table 1). The average rainfall in 2011 was 68.5 mm. The highest precipitation occurred on 26 June and 5 February (about 11.6 mm), which had no runoff. The average reservoir volume and the total capacity of each check dams were estimated at 3239 and 145,744 m3, respectively. During the study period, rainfall events caused 883,139 m3 of floods, of which 433,095 m3 (49%) has stored in check dams reservoirs so that 0.044 was formed by flood sediments. Hence, during the study period, 1947.8 m3 of sediments were deposited in the reservoirs of constructed dams. According to the measurements, 450,044 m3 of flood volume (51%) has left the basin (Table 2). Watershed management operation has provided good conditions for rainwater harvesting and infiltration at upstream of the study area. While before the implementation of watershed management, all flood flows were out of reach after a short time. During the study period, 5,920,276 m3 of rainfall has occurred in the region, which has led to the creation of 1,430,614 m3 of runoff. Meanwhile, watershed management operation has caused storage and infiltration of 840,571 m3 of flood volume in the reservoirs of structures, and only 590,043 m3 of it has left the basin. On the other hand, if the studied structures were not built in this basin, 1,430,614 m3 of runoff volume not only was leaving the basin, but also was increasing the destructive power of flood flows. This shows that watershed management operations are efficient in rainwater harvesting and controlling soil loss. A comparison of runoff volume before and after watershed management is shown in Fig. 2. According to the results, there is a significantly different between the volume of runoff before and after watershed management operation (Table 3). After watershed management operation, the runoff enters the reservoirs of the constructed dams, and after filling them, it flows to downstream. Structures act as regulators of stream flow and increase runoff continuity. In addition, the peak discharge volume greatly decreases due to mechanical and biological barriers. For example, a 5-h flood hydrograph in this basin, which has a base flow, shows that with the onset of rainfall, its outflow significantly increased, while after the cessation of rainfall, discharge gradually decreased (Fig. 3). Findings indicate that at 1, 2, 5, 10, 15, 20, 20, 25, and 30 min, the penetration rate was equivalent to 5, 3, 3, 2, 2, 2, 2, 2, and 2 mm, respectively. Also, investigation of penetration speed at different times shows that in 150 and 180 min, penetration speeds were 0.7 and 0.6 (mm/min), respectively (Fig. 4). Examination of flow duration after rainfall events in the study area shows that, before the implementation of watershed management, with a rainfall of 10 mm per hour, flood was producing, and after rainfall cessation, up to 6 h later, flood was stopping. Whereas, after the implementation of watershed management operations, rainfall of more than 30 mm per hour was producing runoff at the basin outlet. However, its flow duration increased to 10 and 20 days after rainfall, at a height of 10 and 20 cm, respectively (Fig. 5). As depicted in Figs. 6 and 7, after watershed management operation (2017), the area of flood farming in sub-basins A, B, C, and D compare to non-implementation conditions (2004) increased to 55.36%, 54.7%, 61.3%, and 69.4%, respectively. Also, the results show that the garden area compare to non-implementation conditions significantly increased (72.1%, 16.7%, 66.1%, and 77.5%, respectively).

Table 1 Precipitation data of the studied watershed in 2010
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Table 2 The extent of flood control through the reservoirs of structures
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Fig. 2
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Comparison of runoff volume before and after watershed management operation

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Table 3 Result of comparison volume of runoff before and after watershed management
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Fig. 3
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5-h rainfall flood hydrograph in this basin

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Fig. 4
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Showing Horton’s infiltration curve at various times

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Fig. 5
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Flow duration before and after watershed management

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Fig. 6
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Classification of flood farming and garden land area before (I) and after (II) watershed management operation in study area

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Fig. 7
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Comparison changes of flood farming land (a) and garden land (b) before (2004) and after (2017) watershed management operation in the study area

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Discussion

Precipitation drainage into the main river in the watershed causes flood flow, which has strong destructive powers (Koem et al. 2019; Al Habib et al. 2020). These floods cause soil erosion and destroy potential agricultural lands along rivers. When the capacity of channels is low, the flood speed and its destructive power increase (Maryono 2018; Emily et al. 2020; Krätzschmar et al. 2022). Hence, the implementation of watershed management operations, especially in arid areas, is one of the basic needs to stabilize the ecosystem and use available resources optimally for sustainability and development in these regions. Accordingly, this operation requires a well-planned, so that, in addition to high performance, it is economically viable too. In this regard, the construction of check dams in waterways, based on the scientific principles of watershed management, decreases flood risk in upstream waterways. So, these structures prevent to runoff junction of waterways in upper and also reduce runoff volume. Such a mechanism mitigates the velocity of concentrated flood flows and contributes to improve runoff infiltration at the upstream regions. In other words, check dams construction by reducing peak flow discharges and runoff volumes significantly increased the runoff infiltration in the upstream regions. So that finding represented that the effect of check dams contributed 2.4 times to decrease runoff volume during the study period. As well, results showed that the system of check dams, by storing floods, substantially increased runoff infiltration (59%). The reason for this mechanism is related to the soil characteristics of the study area. Because the soil texture at the upper section of the study area is light with high pore, consequently, most of the runoff volume due to heavy rainfall in these control points gradually infiltrates the groundwater. Roughani et al. (2011) have also achieved such results by studying the Bardeh watershed in the southwest Iran. They reported that, with the implementation of these structures, in addition to the runoff infiltration at upstream, soil stabilization has also taken place. This process influences the hydrological response of the watershed and effectively mitigates flood processes in this area. Yuan et al. (2022) reported that the construction of check dams substantially decreased the runoff coefficient and by increasing the capacity of storing floods has promoted runoff infiltration. This mechanism effectively reduces sediment transport. As a result, during the study period, 1947.8 m3 of sediment was deposited in the reservoirs of constructed dams. The results of Li et al. (2017) also showed that the implementation of check dams by modifying the hydrological responses in the catchment reduces flooding risk and sediment transport. Research results showed that the construction of check dams as an engineering structure is useful for soil and water conservation and achieves to sustainability and ecosystem development in the watershed basin (Roughani et al. 2011; Zhao et al. 2016; Tang et al. 2020). In accordance with the results, constructing different check dams in the studied watershed has efficiently contributed to control and storage surface runoff. This process is a suitable solution to meet an important part of the water required for farmers and ranchers. Based on the results, after watershed management operation, due to the increase in water available resources to crop production and livestock, the area of garden and flood farming lands significantly increased. Palanisami and Kumar (2009) have found that watershed management activities have major effects on biophysical, environmental, and socio-economic development. So increasing agricultural lands is one of the effects of mechanical structures in this region (Fig. 7). Also, some reports show that watershed management operation has played an important role in controlling surface runoff and increasing yields in watersheds (Karbowski 1993; Zhu et al. 2004; Bombino et al. 2009; Jahantigh 2017).

Overall, implementation of watershed management operations by check dams construction in the Taftan watershed has contributed to control surface runoff and effectively promoted the runoff infiltration and groundwater table that consequently caused farmland for agricultural production has increased. This process has played an important role in soil and water conservation and also environmental sustainability in this area (Fig. 8).

Conclusions

In this research, the impact of watershed management operations on flood reduction and environmental sustainability in the Taftan watershed was studied. The results showed that during the implementation of this research, 840,571m3 of flood volume was stored in the reservoir of check dams, and the amount of runoff infiltration in these control points was increased by 59%. In addition, during the study period, 1947.8 m3 of sediment was deposited in the reservoirs of constructed dams which caused the sediment transport extremely reduced. This process, consequently, caused the area of garden and flood farming lands significantly increased. Therefore, it is concluded that implementation of watershed management operations such as check dams construction, by modifying the hydrological responses in the watershed, not only has effects on the hydrology process, but also has positive ecological and environmental effects to achieve sustainability and ecosystem development in watersheds. Hence, to maintain the ecosystem functions of watersheds, especially in arid areas, training and management based on watershed management approaches can create important synergies to improve the socio-economic condition and environmental services in watershed basins.

Fig. 8
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View of impacts of watershed management activities on environmental and agricultural condition in the Taftan watershed

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To obtain satisfactory results from watershed management operations in the Taftan watershed, it is necessary to take into account maintenance requirements for the stability of structural measures, expansion, and also promotion of watershed management activities in other sub-basins.