**3. Hydrological analysis**

The surface water sub-catchment areas for the upper Lunan Water have been separated, for water balance purposes, into the areas used for hydraulic modelling, which are shown in **Figure 2**. The areas of each of these sub-catchments were used to scale measured and modelled flows from monitored sub-catchments where water flow and water quality monitoring occurred. These are the Balgavies Burn sub-catchment, at Westerton (area = 4.4 km2 ), which generates real time stage and flow data and the Baldardo Burn sub-catchment at Wemyss (area = 2.4 km2 ), which generates water level data.

The "Water for All" project focused on the outlet zone of Balgavies Loch (**Figure 3**), where the Lunan Water discharges into a partially confined common channel (lade). This lade controls water delivery to a mill or returning to the river, controlled by an existing engineered gated weir, and water also flows from the river into to its lateral floodplain wetlands (Chapel Mires) via a non-engineered spillage zone, which replaced a now-blocked engineered spillway in the 1970's. The ecological value of these wetlands may be vulnerable due to ingress of sediment and

**Figure 2.** *Sub-catchments of upper Lunan water used in hydrological-hydraulic modelling.*

*The Challenges of Managing Water for Wetland Ecology, Flood Mitigation and Agriculture… DOI: http://dx.doi.org/10.5772/intechopen.98727*

#### **Figure 3.**

*Outlet structures of Balgavies loch to Lunan water. Bed levels shown in red in m above sea level. RET = return gate from common lade to Lunan water; CMS = existing chapel mires spillway; TIW1, TIW2 = possible sites for installation of tilting weir to manage flow routing and upstream water levels. Figures in red are elevation of bed level of stream above sea level in metres.*

#### **Figure 4.**

*Observed water levels in Balgavies loch over Oct 2020-Feb 2021 compared with results of simulations using the hydrological model with two alternative assumptions: a. using observed rainfall b. using rainfall from the 1d forecast on a 2x2km2 grid, updated daily from the UK meteorological office.*

nutrients from the river [12, 14]. Hydro-ecological assessment involved developing a model of the upper Lunan Water and the operation of this outlet zone. The aim of the modelling is to generate a time series of historic, real-time and forecast based surface water and ground water flows and water levels in the upper Lunan Water catchment, whose area is defined by the surface water outlet at Milldens bridge (Grid Reference NO 354526 750566). These could then be used to provide triggers or other guidance for hydraulic management. This model is now running in a real time and forecasting mode.1

The hydrological-hydraulic model has the capability to simulate water levels in the upper Lunan Water lakes as illustrated in **Figure 4**, and flow routing between the Common Lade and the Lunan Water.

<sup>1</sup> https://www.hutton.ac.uk/research/projects/payments-ecosystem-services-lessons#waterforall

The model calibration provided the basis for some level of certainty about the impact of existing and potential hydraulic management. The scenario analysis pointed to the rather low impact of installation of a tilting weir on upstream water levels, whether this were to be installed either above or below the confluence of the Balgavies Burn and the Common Lade. However, it also pointed to a larger impact on water levels if dredging/vegetation management or other interventions that affect the Manning roughness coefficient downstream of Balgavies Loch are undertaken, in conjunction with tilting weir installation. It also shows that flow routing could be significantly impacted by a tilting weir, or by reinstatement of the blocked spillway downstream of the current spillway (see **Figure 3**), especially if combined with local dredging and/or vegetation management.
