*2.2. Methods*

The research was conducted at point locations L and Q by collecting data on the water level, rainfall, and pH, which were obtained by direct observation through the telemetry monitoring system shown in Figure 2.

**Figure 2.** The Dadahup Swamp Irrigation Monitoring Telemetry System.

#### *2.3. Characteristics of the Dadahup Swamp Irrigation Area*

Hydro-topography is the relationship between the water table elevation and land elevation, which is a factor in determining the classification type of the swamp irrigation areas, as shown in Figure 3 [7]. The Dadahup Swamp Irrigation Area falls into categories C

and D, where the tidal water level never inundates the land elevation; so, the main source of water is rainfall, which is included in the nontidal swamp category shown in Figure 4 [8]. The characteristics of the soil, which is dominated by pyrite peat soil, can reduce the water quality and have a negative impact on rice growth [9]. The polder water system is one of the solutions for the development of the Dadahup Swamp Irrigation Area by utilizing rainfall as a water source by isolating the land, which is regulated through the operation of gate buildings in the north, east, west, and south [10].

(**a**)

**Figure 3.** (**a**) Tidal Swamp Hydro-topography and (**b**) Nontidal Swamp Hydro-topography.

**Figure 4.** Hydro-topography Map of the Dadahup Swamp Irrigation Area.

### *2.4. Water Quantity and Quality*

The tidal influence of the estuary and the upstream discharge of the Barito River can affect the water level at the intake channel of the Dadahup Swamp Irrigation Area with a distance of up to 158 km to the upstream of the river [11]. The Dadahup Irrigation Area is included in the wet category of climate types B and E, where the rainy season occurs from May to October, and the dry season occurs from November to April. The swamp soil characteristics are influenced by the presence of pyrite formed from marine deposits containing organic matter and sulfate-reducing bacteria. The oxidation of pyrite can cause high acidity, which produces sulfuric acid and jarosite minerals that reduce the pH concentration and interfere with plant growth [12].

### **3. Results and Discussion**

### *3.1. Water Quantity Dynamics Profile*

The dynamics of the water quantity illustrate the profile of the relationship between the rainfall and water level during the dry and wet seasons at points L and Q in the main primary channel shown in Figures 5 and 6.

**Figure 5.** Water Level Dynamics Profile in the Dry Season in the Upper and Middle Sections of the Dadahup Swamp Irrigation Area.

**Figure 6.** Water Level Dynamics Profile in the Rainy Season in the Upper and Middle Sections of the Dadahup Swamp Irrigation Area.

Based on the results of the description of the dynamic profile of the water level at points L and Q for the dry season and the rainy season, there was a change in the water level elevation influenced by the rainfall with an average increase of 0.3 m, which is shown in Table 1.


**Table 1.** Changes in the Water Level during the Dry and Rainy Seasons at Points L and Q.

### *3.2. Water Quality Dynamics Profile*

The water quality dynamics illustrate the relationship profile of the pH during the dry and wet seasons. The results of the water quality dynamics profile at point L upstream and point Q midstream of the Dadahup Swamp Irrigation Area during the dry and wet seasons are shown in Figures 7 and 8.

**Figure 7.** Water Quality Dynamics Profile in the Dry Season in the Upper and Middle Sections of the Dadahup Swamp Irrigation Area.

**Figure 8.** Water Quality Dynamics Profile in the Rainy Season in the Upper and Middle Sections of the Dadahup Swamp Irrigation Area.

Based on the results of the description of the dynamic profile of the water quality, there was a change in the pH value influenced by the rainfall with an average increase reaching level 3, which is shown in Table 2.

**Table 2.** Changes in the pH Values during the Dry and Rainy Seasons in the Upper and Middle Sections of the Dadahup Irrigation Area.

